From 6ca01668a6cf469a71493364e1de54c15c7f35ea Mon Sep 17 00:00:00 2001
From: Sandeep Somavarapu <sasomava@microsoft.com>
Date: Tue, 8 Sep 2026 16:48:50 +0200
Subject: [PATCH 1/4] sessions: add explicit worktree option to create_session

Honor user-requested worktree overrides while preserving isolation inheritance when omitted. Reject overrides for current-session chats and resolve known worktree folders to their project root when worktree is false.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/vs/platform/agentHost/AGENTS.md           |  15 +-
 .../node/shared/sessionServerTools.ts         |  27 ++-
 .../test/node/sessionServerTools.test.ts      | 160 +++++++++++++++++-
 3 files changed, 188 insertions(+), 14 deletions(-)

diff --git a/src/vs/platform/agentHost/AGENTS.md b/src/vs/platform/agentHost/AGENTS.md
index b7c44861ec506..d9673ba232099 100644
--- a/src/vs/platform/agentHost/AGENTS.md
+++ b/src/vs/platform/agentHost/AGENTS.md
@@ -244,7 +244,8 @@ Treat a session as the user-visible unit of work. `create_session` requires a
 relationship: `currentSession` creates a peer chat for tasks in the current plan
 or deliverable, sharing its workspace, lifecycle, and aggregate diff;
 `independent` creates a top-level session for a separate deliverable that needs
-its own workspace, provider, or lifecycle. A title is required for both
+its own workspace, provider, or lifecycle, or for an explicitly requested
+worktree. A title is required for both
 relationships and is applied before the initial prompt starts.
 
 Sessions created by the `create_session` server tool record only the creating
@@ -261,9 +262,15 @@ configured project root over a transient worktree. Ambiguous names require an
 explicit project URI.
 
 An independent session inherits the creating session's host-owned isolation
-selection independently of provider-owned configuration. The target workspace
-still constrains the effective selection, so a folder that cannot support Git
-worktrees resolves to folder isolation.
+selection independently of provider-owned configuration;
+otherwise it uses worktree isolation. The optional `worktree` argument overrides
+that selection. Agents must set it only when the user explicitly asks to create a
+worktree (`true`) or work without one (`false`); otherwise they must omit it.
+With `false`, a supplied worktree folder resolves to its known project root
+before session creation; folders without a known project are used directly.
+The option is invalid with `currentSession`, whose chats share the existing
+workspace. The target workspace still constrains the effective selection, so a
+folder that cannot support Git worktrees resolves to folder isolation.
 
 ---
 
diff --git a/src/vs/platform/agentHost/node/shared/sessionServerTools.ts b/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
index dad63d53cdf6d..922078123f4ec 100644
--- a/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
+++ b/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
@@ -73,10 +73,11 @@ const createSessionInputSchema: ToolDefinition['inputSchema'] = {
 		relationship: {
 			type: 'string',
 			enum: [...createSessionRelationshipValues],
-			description: 'Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle.',
+			description: 'Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree.',
 		},
 		prompt: { type: 'string', description: 'Initial prompt to send to the new session.' },
 		workspace: { type: 'string', description: 'For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`.' },
+		worktree: { type: 'boolean', description: 'Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session\'s isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`.' },
 		title: { type: 'string', maxLength: 200, description: 'Short title for the new chat or independent session.' },
 		model: { type: 'string', description: 'Optional model ID or display name. Defaults to the current chat\'s model. For `currentSession`, the model must belong to the current session\'s provider; for `independent`, the model selects the new session\'s provider.' },
 	},
@@ -173,7 +174,7 @@ export const sessionServerToolDefinitions: IAgentServerToolDefinition[] = [
 	{
 		name: SessionServerToolName.CreateSession,
 		title: 'Create Session',
-		description: 'Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session\'s workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.',
+		description: 'Create delegated work and start it with an initial prompt, either in a new chat sharing the current session\'s workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.',
 		inputSchema: createSessionInputSchema,
 		annotations: { readOnlyHint: false },
 	},
@@ -216,6 +217,7 @@ export function currentSessionUri(toolCallChannel: ProtocolURI): URI {
 interface ICreateSessionArgs {
 	readonly relationship?: unknown;
 	readonly workspace?: unknown;
+	readonly worktree?: unknown;
 	readonly prompt?: unknown;
 	readonly title?: unknown;
 	readonly model?: unknown;
@@ -229,6 +231,7 @@ export type IResolvedCreateSessionArgs = {
 } | {
 	readonly relationship: 'independent';
 	readonly workspace: URI;
+	readonly worktree?: boolean;
 	readonly prompt: string;
 	readonly title: string;
 	readonly model?: IAgentModelInfo;
@@ -429,12 +432,12 @@ export function getSetWorkspaceArgs(rawArgs: unknown): { readonly workspaceFolde
 	};
 }
 
-function resolveWorkspace(workspace: string, sessions: readonly IAgentSessionMetadata[]): URI {
+function resolveWorkspace(workspace: string, sessions: readonly IAgentSessionMetadata[], preferProject = false): URI {
 	const parsed = parseWorkspaceUri(workspace);
 	for (const session of sessions) {
 		for (const candidate of [session.project?.uri, ...(session.workingDirectories ?? [])]) {
 			if (candidate && parsed && isEqual(candidate, parsed)) {
-				return candidate;
+				return preferProject ? session.project?.uri ?? candidate : candidate;
 			}
 		}
 	}
@@ -515,11 +518,15 @@ export function getCreateSessionArgs(rawArgs: unknown, sessions: readonly IAgent
 	validateRenameTitle(title, SessionServerToolName.CreateSession);
 	const workspace = getOptionalString(args.workspace, 'workspace', SessionServerToolName.CreateSession);
 	const modelName = getOptionalString(args.model, 'model', SessionServerToolName.CreateSession);
+	const worktree = getOptionalBoolean(args.worktree, 'worktree', SessionServerToolName.CreateSession);
 	const model = resolveModel(modelName, models, relationship === 'currentSession' ? currentProvider : undefined);
 	if (relationship === 'currentSession') {
 		if (workspace !== undefined) {
 			throw new Error(`Invalid ${SessionServerToolName.CreateSession} input: workspace is only valid when relationship is "independent".`);
 		}
+		if (worktree !== undefined) {
+			throw new Error(`Invalid ${SessionServerToolName.CreateSession} input: worktree is only valid when relationship is "independent"; chats in the current session share its workspace.`);
+		}
 		return {
 			relationship,
 			prompt,
@@ -529,7 +536,8 @@ export function getCreateSessionArgs(rawArgs: unknown, sessions: readonly IAgent
 	}
 	return {
 		relationship,
-		workspace: resolveWorkspace(getRequiredString(workspace, 'workspace', SessionServerToolName.CreateSession), sessions),
+		workspace: resolveWorkspace(getRequiredString(workspace, 'workspace', SessionServerToolName.CreateSession), sessions, worktree === false),
+		...(worktree !== undefined ? { worktree } : {}),
 		prompt,
 		title,
 		...(model !== undefined ? { model } : {}),
@@ -821,9 +829,12 @@ export async function applyCreateSessionTool(accessor: ISessionServerToolAccesso
 	const provider = args.model?.provider ?? defaults?.provider;
 	const inheritsSourceProvider = provider !== undefined && provider === defaults?.provider;
 	const inheritedProviderConfig = inheritsSourceProvider ? defaults?.config : undefined;
-	const isolation = defaults?.project !== undefined && isEqual(defaults.project, args.workspace)
-		? defaults.isolation
-		: 'worktree';
+	let isolation: 'folder' | 'worktree' | undefined = 'worktree';
+	if (args.worktree !== undefined) {
+		isolation = args.worktree ? 'worktree' : 'folder';
+	} else if (defaults?.project !== undefined && isEqual(defaults.project, args.workspace)) {
+		isolation = defaults.isolation;
+	}
 	const configValues = inheritedProviderConfig === undefined && isolation === undefined
 		? undefined
 		: {
diff --git a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
index 327df814b4126..6ef778e0ef635 100644
--- a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
+++ b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
@@ -115,10 +115,11 @@ suite('SessionServerTools', () => {
 				relationship: {
 					type: 'string',
 					enum: ['currentSession', 'independent'],
-					description: 'Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle.',
+					description: 'Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree.',
 				},
 				prompt: { type: 'string', description: 'Initial prompt to send to the new session.' },
 				workspace: { type: 'string', description: 'For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`.' },
+				worktree: { type: 'boolean', description: 'Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session\'s isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`.' },
 				title: { type: 'string', maxLength: 200, description: 'Short title for the new chat or independent session.' },
 				model: { type: 'string', description: 'Optional model ID or display name. Defaults to the current chat\'s model. For `currentSession`, the model must belong to the current session\'s provider; for `independent`, the model selects the new session\'s provider.' },
 			},
@@ -644,6 +645,12 @@ suite('SessionServerTools', () => {
 		});
 	});
 
+	test('create_session guidance requires an explicit isolation choice and excludes currentSession', () => {
+		const description = sessionServerToolDefinitions.find(definition => definition.name === SessionServerToolName.CreateSession)?.description ?? '';
+		assert.match(description, /Only supply `worktree` when the user explicitly requests working with or without a new worktree/);
+		assert.match(description, /never combine it with `currentSession`/);
+	});
+
 	test('getCreateSessionArgs resolves workspace by working directory and model by id/name', () => {
 		const sessions = [sessionMeta('s1', SessionStatus.Idle, workspace)];
 		const byId = getCreateSessionArgs({ relationship: 'independent', workspace: workspace.toString(), prompt: 'hi', title: 'Task', model: 'gpt-4o' }, sessions, [model]);
@@ -698,6 +705,63 @@ suite('SessionServerTools', () => {
 		});
 	});
 
+	for (const scheme of ['file', 'vscode-remote']) {
+		for (const worktree of [false, true, undefined]) {
+			test(`create_session resolves ${scheme} worktree folders to the project only with worktree=false (value=${worktree})`, async () => {
+				const project = URI.from({ scheme, authority: scheme === 'file' ? '' : 'ssh-remote+example', path: '/workspace/repo' });
+				const existingWorktree = project.with({ path: '/worktrees/existing' });
+				let created: IAgentCreateSessionConfig | undefined;
+				const accessor = createAccessor({
+					listSessions: async () => [{
+						...sessionMeta('source', SessionStatus.Idle, existingWorktree),
+						project: { uri: project, displayName: 'Repo' },
+					}],
+					getCreationDefaults: () => ({ provider: 'copilot', project, isolation: 'worktree' }),
+					onCreate: config => { created = config; },
+				});
+
+				await applyCreateSessionTool(accessor, {
+					relationship: 'independent',
+					workspace: scheme === 'file' ? existingWorktree.fsPath : existingWorktree.toString(),
+					...(worktree !== undefined ? { worktree } : {}),
+					prompt: 'do it',
+					title: 'Task',
+				}, URI.parse('copilot:/source'));
+
+				assert.deepStrictEqual({
+					workingDirectories: created?.workingDirectories?.map(directory => directory.toString()),
+					isolation: created?.config?.[SessionConfigKey.Isolation],
+				}, {
+					workingDirectories: [(worktree === false ? project : existingWorktree).toString()],
+					isolation: worktree === false ? 'folder' : 'worktree',
+				});
+			});
+		}
+	}
+
+	test('getCreateSessionArgs preserves folders without a known project when worktree=false', () => {
+		for (const sessions of [[], [sessionMeta('folder', SessionStatus.Idle, workspace)]]) {
+			const args = getCreateSessionArgs({
+				relationship: 'independent',
+				workspace: workspace.toString(),
+				worktree: false,
+				prompt: 'do it',
+				title: 'Task',
+			}, sessions, []);
+
+			assert.deepStrictEqual({
+				...args,
+				workspace: args.relationship === 'independent' ? args.workspace.toString() : undefined,
+			}, {
+				relationship: 'independent',
+				workspace: workspace.toString(),
+				worktree: false,
+				prompt: 'do it',
+				title: 'Task',
+			});
+		}
+	});
+
 	test('getCreateSessionArgs reports ambiguous project names', () => {
 		const sessions = [
 			{ ...sessionMeta('one', SessionStatus.Idle, URI.parse('file:///worktrees/one')), project: { uri: URI.parse('file:///projects/one'), displayName: 'App' } },
@@ -981,7 +1045,7 @@ suite('SessionServerTools', () => {
 		const gitWorkspace = URI.file('/workspace/git-repository');
 		let created: IAgentCreateSessionConfig | undefined;
 		const accessor = createAccessor({
-			getCreationDefaults: () => ({ provider: 'copilot', isolation: 'worktree', project: gitWorkspace }),
+			getCreationDefaults: () => ({ provider: 'copilot', config: { [SessionConfigKey.Isolation]: 'worktree' }, isolation: 'worktree', project: gitWorkspace }),
 			onCreate: config => { created = config; },
 		});
 
@@ -1003,6 +1067,98 @@ suite('SessionServerTools', () => {
 		});
 	});
 
+	for (const worktree of [false, true]) {
+		test(`create_session honors explicit worktree=${worktree} over inherited isolation`, async () => {
+			let created: IAgentCreateSessionConfig | undefined;
+			const accessor = createAccessor({
+				getCreationDefaults: () => ({
+					provider: 'copilot',
+					project: workspace,
+					isolation: worktree ? 'folder' : 'worktree',
+					config: { [SessionConfigKey.Isolation]: worktree ? 'folder' : 'worktree', autoApprove: 'autoApprove' },
+				}),
+				onCreate: config => { created = config; },
+			});
+
+			await applyCreateSessionTool(accessor, {
+				relationship: 'independent',
+				workspace: workspace.toString(),
+				worktree,
+				prompt: 'do it',
+				title: 'Task',
+			}, URI.parse('copilot:/source'));
+
+			assert.deepStrictEqual(created?.config, {
+				[SessionConfigKey.Isolation]: worktree ? 'worktree' : 'folder',
+				autoApprove: 'autoApprove',
+			});
+		});
+
+		test(`create_session rejects currentSession with worktree=${worktree} before creating work`, async () => {
+			const operations: string[] = [];
+			const accessor = createAccessor({
+				onCreate: () => operations.push('session'),
+				onCreateChat: () => operations.push('chat'),
+				onPrompt: () => operations.push('prompt'),
+			});
+
+			await assert.rejects(applyCreateSessionTool(accessor, {
+				relationship: 'currentSession',
+				worktree,
+				prompt: 'do it',
+				title: 'Task',
+			}, URI.parse('copilot:/source')), /worktree is only valid when relationship is "independent"/);
+			assert.deepStrictEqual(operations, []);
+		});
+	}
+
+	test('create_session preserves unspecified isolation for the same project', async () => {
+		let created: IAgentCreateSessionConfig | undefined;
+		const accessor = createAccessor({
+			getCreationDefaults: () => ({ provider: 'copilot', project: workspace }),
+			onCreate: config => { created = config; },
+		});
+
+		await applyCreateSessionTool(accessor, {
+			relationship: 'independent',
+			workspace: workspace.toString(),
+			prompt: 'do it',
+			title: 'Task',
+		}, URI.parse('copilot:/source'));
+
+		assert.deepStrictEqual(created?.config, undefined);
+	});
+
+	test('create_session honors worktree=false for a different project', async () => {
+		let created: IAgentCreateSessionConfig | undefined;
+		const accessor = createAccessor({
+			getCreationDefaults: () => ({ provider: 'copilot', project: URI.file('/workspace/source'), isolation: 'worktree' }),
+			onCreate: config => { created = config; },
+		});
+
+		await applyCreateSessionTool(accessor, {
+			relationship: 'independent',
+			workspace: workspace.toString(),
+			worktree: false,
+			prompt: 'do it',
+			title: 'Task',
+		}, URI.parse('copilot:/source'));
+
+		assert.deepStrictEqual(created?.config, { [SessionConfigKey.Isolation]: 'folder' });
+	});
+
+	test('getCreateSessionArgs rejects non-boolean worktree values', () => {
+		for (const worktree of ['true', 'false', 1, null, {}]) {
+			assert.throws(() => getCreateSessionArgs({
+				relationship: 'independent',
+				workspace: workspace.toString(),
+				worktree,
+				prompt: 'do it',
+				title: 'Task',
+			}, [], []), /worktree must be a boolean/);
+		}
+	});
+
 	test('create_session uses a remote project root with a model from another provider', async () => {
 		const remoteProject = URI.parse('vscode-remote://ssh-remote+example/home/me/app');
 		const remoteWorktree = URI.parse('vscode-remote://ssh-remote+example/home/me/app-worktree');

From 4725615df1c253de959c04dca3586846dbdc7457 Mon Sep 17 00:00:00 2001
From: Sandeep Somavarapu <sasomava@microsoft.com>
Date: Tue, 8 Sep 2026 17:11:04 +0200
Subject: [PATCH 2/4] sessions: preserve folders when disabling worktree
 isolation

Resolve only exact linked-worktree roots reported by Git to the primary checkout. Preserve nested and additional workspace folders instead of inferring worktree identity from session project metadata.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/vs/platform/agentHost/AGENTS.md           |  5 +-
 .../platform/agentHost/node/agentService.ts   |  1 +
 .../agentHost/node/agentServiceFoundation.ts  |  1 +
 .../node/shared/sessionServerTools.ts         | 18 ++--
 .../test/node/sessionServerTools.test.ts      | 86 ++++++++++++++++++-
 5 files changed, 103 insertions(+), 8 deletions(-)

diff --git a/src/vs/platform/agentHost/AGENTS.md b/src/vs/platform/agentHost/AGENTS.md
index d9673ba232099..2f4bc50e06b8b 100644
--- a/src/vs/platform/agentHost/AGENTS.md
+++ b/src/vs/platform/agentHost/AGENTS.md
@@ -266,8 +266,9 @@ selection independently of provider-owned configuration;
 otherwise it uses worktree isolation. The optional `worktree` argument overrides
 that selection. Agents must set it only when the user explicitly asks to create a
 worktree (`true`) or work without one (`false`); otherwise they must omit it.
-With `false`, a supplied worktree folder resolves to its known project root
-before session creation; folders without a known project are used directly.
+With `false`, an exact linked-worktree root reported by Git resolves to its
+primary checkout before session creation. Nested and ordinary additional
+workspace folders are preserved.
 The option is invalid with `currentSession`, whose chats share the existing
 workspace. The target workspace still constrains the effective selection, so a
 folder that cannot support Git worktrees resolves to folder isolation.
diff --git a/src/vs/platform/agentHost/node/agentService.ts b/src/vs/platform/agentHost/node/agentService.ts
index 36c53366234f1..853ce5afbff52 100644
--- a/src/vs/platform/agentHost/node/agentService.ts
+++ b/src/vs/platform/agentHost/node/agentService.ts
@@ -1178,6 +1178,7 @@ export class AgentService extends Disposable implements IAgentService {
 				&& readSessionWorkspaceless(this._stateManager.getSessionState(session.toString())?._meta),
 			listSessions: () => this.listSessions(),
 			getSession: session => this._getSessionMetadata(session),
+			getWorktreeRoots: workspace => this._gitService.getWorktreeRoots(workspace),
 			createSession: config => this.createSession(config),
 			getModels: () => {
 				const models: IAgentModelInfo[] = [];
diff --git a/src/vs/platform/agentHost/node/agentServiceFoundation.ts b/src/vs/platform/agentHost/node/agentServiceFoundation.ts
index 8506160d570ad..a4461a63d4883 100644
--- a/src/vs/platform/agentHost/node/agentServiceFoundation.ts
+++ b/src/vs/platform/agentHost/node/agentServiceFoundation.ts
@@ -39,6 +39,7 @@ export class AgentServiceCallbackAdapter implements IAgentServiceCallbackBinder
 		canConvertWorkspace: session => this.value.sessionServerToolAccessor.canConvertWorkspace(session),
 		listSessions: () => this.value.sessionServerToolAccessor.listSessions(),
 		getSession: session => this.value.sessionServerToolAccessor.getSession(session),
+		getWorktreeRoots: workspace => this.value.sessionServerToolAccessor.getWorktreeRoots(workspace),
 		createSession: config => this.value.sessionServerToolAccessor.createSession(config),
 		getModels: () => this.value.sessionServerToolAccessor.getModels(),
 		getCreationDefaults: source => this.value.sessionServerToolAccessor.getCreationDefaults(source),
diff --git a/src/vs/platform/agentHost/node/shared/sessionServerTools.ts b/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
index 922078123f4ec..ce925bb291cf0 100644
--- a/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
+++ b/src/vs/platform/agentHost/node/shared/sessionServerTools.ts
@@ -243,6 +243,7 @@ export interface IAgentServiceSessionServerToolAccessor {
 	readonly canConvertWorkspace: (session: URI) => boolean;
 	readonly listSessions: () => Promise<readonly IAgentSessionMetadata[]>;
 	readonly getSession: (session: URI) => Promise<IAgentSessionMetadata | undefined>;
+	readonly getWorktreeRoots: (workspace: URI) => Promise<readonly URI[]>;
 	readonly createSession: (config: IAgentCreateSessionConfig) => Promise<URI>;
 	readonly getModels: () => readonly IAgentModelInfo[];
 	readonly getCreationDefaults: (source: URI) => ISessionCreationDefaults | undefined;
@@ -432,12 +433,12 @@ export function getSetWorkspaceArgs(rawArgs: unknown): { readonly workspaceFolde
 	};
 }
 
-function resolveWorkspace(workspace: string, sessions: readonly IAgentSessionMetadata[], preferProject = false): URI {
+function resolveWorkspace(workspace: string, sessions: readonly IAgentSessionMetadata[]): URI {
 	const parsed = parseWorkspaceUri(workspace);
 	for (const session of sessions) {
 		for (const candidate of [session.project?.uri, ...(session.workingDirectories ?? [])]) {
 			if (candidate && parsed && isEqual(candidate, parsed)) {
-				return preferProject ? session.project?.uri ?? candidate : candidate;
+				return candidate;
 			}
 		}
 	}
@@ -536,7 +537,7 @@ export function getCreateSessionArgs(rawArgs: unknown, sessions: readonly IAgent
 	}
 	return {
 		relationship,
-		workspace: resolveWorkspace(getRequiredString(workspace, 'workspace', SessionServerToolName.CreateSession), sessions, worktree === false),
+		workspace: resolveWorkspace(getRequiredString(workspace, 'workspace', SessionServerToolName.CreateSession), sessions),
 		...(worktree !== undefined ? { worktree } : {}),
 		prompt,
 		title,
@@ -825,6 +826,13 @@ export async function applyCreateSessionTool(accessor: ISessionServerToolAccesso
 	if (parentDepth >= maxSessionSpawnDepth) {
 		throw new Error(`Refusing to create a session: recursion limit reached (max spawn depth ${maxSessionSpawnDepth}). This session was itself created ${parentDepth} level(s) deep.`);
 	}
+	let workspace = args.workspace;
+	if (args.worktree === false) {
+		const [primaryRoot, ...linkedRoots] = await accessor.getWorktreeRoots(workspace);
+		if (primaryRoot && linkedRoots.some(root => isEqual(root, workspace))) {
+			workspace = primaryRoot;
+		}
+	}
 	const defaults = source ? accessor.getCreationDefaults(source) : undefined;
 	const provider = args.model?.provider ?? defaults?.provider;
 	const inheritsSourceProvider = provider !== undefined && provider === defaults?.provider;
@@ -832,7 +840,7 @@ export async function applyCreateSessionTool(accessor: ISessionServerToolAccesso
 	let isolation: 'folder' | 'worktree' | undefined = 'worktree';
 	if (args.worktree !== undefined) {
 		isolation = args.worktree ? 'worktree' : 'folder';
-	} else if (defaults?.project !== undefined && isEqual(defaults.project, args.workspace)) {
+	} else if (defaults?.project !== undefined && isEqual(defaults.project, workspace)) {
 		isolation = defaults.isolation;
 	}
 	const configValues = inheritedProviderConfig === undefined && isolation === undefined
@@ -842,7 +850,7 @@ export async function applyCreateSessionTool(accessor: ISessionServerToolAccesso
 			...(isolation !== undefined ? { [SessionConfigKey.Isolation]: isolation } : {}),
 		};
 	const config: IAgentCreateSessionConfig = {
-		workingDirectories: args.workspace ? [args.workspace] : undefined,
+		workingDirectories: [workspace],
 		...(provider !== undefined ? { provider } : {}),
 		...(args.model !== undefined ? { model: { id: args.model.id } } : defaults?.model !== undefined ? { model: defaults.model } : {}),
 		...(configValues !== undefined ? { config: configValues } : {}),
diff --git a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
index 6ef778e0ef635..8e295cdd5b476 100644
--- a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
+++ b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
@@ -68,6 +68,7 @@ suite('SessionServerTools', () => {
 			canConvertWorkspace: overrides?.canConvertWorkspace ?? (() => true),
 			listSessions: overrides?.listSessions ?? (async () => [sessionMeta('s1', SessionStatus.InProgress, workspace)]),
 			getSession: overrides?.getSession ?? (async session => session.toString() === 'copilot:/s1' ? sessionMeta('s1', SessionStatus.InProgress, workspace) : undefined),
+			getWorktreeRoots: overrides?.getWorktreeRoots ?? (async () => []),
 			createSession: overrides?.createSession ?? (async config => { overrides?.onCreate?.(config); return URI.parse('copilot:/new'); }),
 			getModels: overrides?.getModels ?? (() => [model]),
 			getCreationDefaults: overrides?.getCreationDefaults ?? (() => undefined),
@@ -707,7 +708,7 @@ suite('SessionServerTools', () => {
 
 	for (const scheme of ['file', 'vscode-remote']) {
 		for (const worktree of [false, true, undefined]) {
-			test(`create_session resolves ${scheme} worktree folders to the project only with worktree=false (value=${worktree})`, async () => {
+			test(`create_session resolves ${scheme} linked worktree roots only with worktree=false (value=${worktree})`, async () => {
 				const project = URI.from({ scheme, authority: scheme === 'file' ? '' : 'ssh-remote+example', path: '/workspace/repo' });
 				const existingWorktree = project.with({ path: '/worktrees/existing' });
 				let created: IAgentCreateSessionConfig | undefined;
@@ -717,6 +718,11 @@ suite('SessionServerTools', () => {
 						project: { uri: project, displayName: 'Repo' },
 					}],
 					getCreationDefaults: () => ({ provider: 'copilot', project, isolation: 'worktree' }),
+					getWorktreeRoots: async directory => {
+						assert.strictEqual(directory.toString(), existingWorktree.toString());
+						assert.strictEqual(worktree, false);
+						return [project, existingWorktree];
+					},
 					onCreate: config => { created = config; },
 				});
 
@@ -739,6 +745,84 @@ suite('SessionServerTools', () => {
 		}
 	}
 
+	test('create_session with worktree=false preserves nested and additional workspace folders', async () => {
+		const project = URI.file('/repo');
+		const linkedRoot = URI.file('/worktrees/linked');
+		const nestedFolder = URI.file('/repo/packages/foo');
+		const linkedNestedFolder = URI.file('/worktrees/linked/packages/foo');
+		const additionalRoot = URI.file('/other');
+		const plainFolder = URI.file('/plain');
+		const created: (string[] | undefined)[] = [];
+		const accessor = createAccessor({
+			listSessions: async () => [{
+				...sessionMeta('source', SessionStatus.Idle, nestedFolder),
+				workingDirectories: [nestedFolder, additionalRoot, linkedNestedFolder, plainFolder],
+				project: { uri: project, displayName: 'Repo' },
+			}],
+			getWorktreeRoots: async directory => {
+				if (directory.toString() === additionalRoot.toString()) {
+					return [additionalRoot];
+				}
+				if (directory.toString() === plainFolder.toString()) {
+					return [];
+				}
+				return [project, linkedRoot];
+			},
+			onCreate: config => created.push(config.workingDirectories?.map(directory => directory.toString())),
+		});
+
+		for (const directory of [project, nestedFolder, linkedNestedFolder, additionalRoot, plainFolder]) {
+			await applyCreateSessionTool(accessor, {
+				relationship: 'independent',
+				workspace: directory.toString(),
+				worktree: false,
+				prompt: 'do it',
+				title: 'Task',
+			});
+		}
+
+		assert.deepStrictEqual(created, [project, nestedFolder, linkedNestedFolder, additionalRoot, plainFolder].map(directory => [directory.toString()]));
+	});
+
+	test('create_session with worktree=false resolves linked roots without session metadata', async () => {
+		const project = URI.file('/repo');
+		const linkedRoot = URI.file('/worktrees/linked');
+		let created: IAgentCreateSessionConfig | undefined;
+		const accessor = createAccessor({
+			listSessions: async () => [],
+			getWorktreeRoots: async () => [project, linkedRoot],
+			onCreate: config => { created = config; },
+		});
+
+		await applyCreateSessionTool(accessor, {
+			relationship: 'independent',
+			workspace: linkedRoot.toString(),
+			worktree: false,
+			prompt: 'do it',
+			title: 'Task',
+		});
+
+		assert.deepStrictEqual(created?.workingDirectories?.map(directory => directory.toString()), [project.toString()]);
+	});
+
+	test('create_session propagates worktree lookup failures before creating a session', async () => {
+		const operations: string[] = [];
+		const accessor = createAccessor({
+			getWorktreeRoots: async () => { throw new Error('Worktree lookup failed'); },
+			onCreate: () => operations.push('create'),
+			onPrompt: () => operations.push('prompt'),
+		});
+
+		await assert.rejects(applyCreateSessionTool(accessor, {
+			relationship: 'independent',
+			workspace: workspace.toString(),
+			worktree: false,
+			prompt: 'do it',
+			title: 'Task',
+		}), /Worktree lookup failed/);
+		assert.deepStrictEqual(operations, []);
+	});
+
 	test('getCreateSessionArgs preserves folders without a known project when worktree=false', () => {
 		for (const sessions of [[], [sessionMeta('folder', SessionStatus.Idle, workspace)]]) {
 			const args = getCreateSessionArgs({

From 9a8d2b79c53df0bbe367ef9ab82523a4465de736 Mon Sep 17 00:00:00 2001
From: Sandeep Somavarapu <sasomava@microsoft.com>
Date: Tue, 8 Sep 2026 18:32:39 +0200
Subject: [PATCH 3/4] sessions: fix worktree tests and refresh tool prompt
 snapshots

Use drive-qualified paths for Windows filesystem test inputs and regenerate Copilot prompt baselines for the explicit worktree tool option.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 ..._Host_E2E___Copilot_prompts_claude-haiku-4_5.prompt.md | 8 ++++++--
 ...t_Host_E2E___Copilot_prompts_claude-opus-4_5.prompt.md | 8 ++++++--
 ...t_Host_E2E___Copilot_prompts_claude-opus-4_6.prompt.md | 8 ++++++--
 ...t_Host_E2E___Copilot_prompts_claude-opus-4_7.prompt.md | 8 ++++++--
 ...t_Host_E2E___Copilot_prompts_claude-opus-4_8.prompt.md | 8 ++++++--
 ...ent_Host_E2E___Copilot_prompts_claude-opus-5.prompt.md | 8 ++++++--
 ...Host_E2E___Copilot_prompts_claude-sonnet-4_5.prompt.md | 8 ++++++--
 ...Host_E2E___Copilot_prompts_claude-sonnet-4_6.prompt.md | 8 ++++++--
 ...t_Host_E2E___Copilot_prompts_claude-sonnet-5.prompt.md | 8 ++++++--
 ..._Host_E2E___Copilot_prompts_gemini-2_0-flash.prompt.md | 8 ++++++--
 ...Agent_Host_E2E___Copilot_prompts_gpt-5-codex.prompt.md | 8 ++++++--
 .../Agent_Host_E2E___Copilot_prompts_gpt-5-mini.prompt.md | 8 ++++++--
 .../Agent_Host_E2E___Copilot_prompts_gpt-5.prompt.md      | 8 ++++++--
 ...ost_E2E___Copilot_prompts_gpt-5_1-codex-mini.prompt.md | 8 ++++++--
 ...ent_Host_E2E___Copilot_prompts_gpt-5_1-codex.prompt.md | 8 ++++++--
 .../Agent_Host_E2E___Copilot_prompts_gpt-5_1.prompt.md    | 8 ++++++--
 ...gent_Host_E2E___Copilot_prompts_gpt-5_6-luna.prompt.md | 8 ++++++--
 ...Agent_Host_E2E___Copilot_prompts_gpt-5_6-sol.prompt.md | 8 ++++++--
 ...ent_Host_E2E___Copilot_prompts_gpt-5_6-terra.prompt.md | 8 ++++++--
 .../agentHost/test/node/sessionServerTools.test.ts        | 6 ++++--
 20 files changed, 118 insertions(+), 40 deletions(-)

diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-haiku-4_5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-haiku-4_5.prompt.md
index 224bd3aa3ca00..e42c352951bf9 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-haiku-4_5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-haiku-4_5.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_5.prompt.md
index 88d3faa90ed74..b69997595dfc2 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_5.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_6.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_6.prompt.md
index fc7650db5b919..6ddab93b58574 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_6.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_6.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_7.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_7.prompt.md
index a8f698a3b51f4..f377b1c2fadc0 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_7.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_7.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_8.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_8.prompt.md
index 4f6e9c308c01e..b8631a4a9992b 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_8.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-4_8.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-5.prompt.md
index 38fc3b56132e6..f822d904c6581 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-opus-5.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_5.prompt.md
index 3bde585137ef7..424a08bd1098d 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_5.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_6.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_6.prompt.md
index 2d306031176b4..a4354931e8198 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_6.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-4_6.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-5.prompt.md
index 969abbe8fb4f5..8d997ba4df01e 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_claude-sonnet-5.prompt.md
@@ -733,7 +733,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "input_schema": {
         "type": "object",
         "properties": {
@@ -743,7 +743,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -753,6 +753,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gemini-2_0-flash.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gemini-2_0-flash.prompt.md
index 7bec1bc62d023..40fa1b9b2d167 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gemini-2_0-flash.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gemini-2_0-flash.prompt.md
@@ -765,7 +765,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -775,7 +775,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -785,6 +785,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-codex.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-codex.prompt.md
index 4589a2396b3f1..ae4606be3e29d 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-codex.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-codex.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-mini.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-mini.prompt.md
index 063a87373067e..96ec9caa3908d 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-mini.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5-mini.prompt.md
@@ -765,7 +765,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -775,7 +775,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -785,6 +785,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5.prompt.md
index 180e0a9031009..044dcfda39962 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5.prompt.md
@@ -765,7 +765,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -775,7 +775,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -785,6 +785,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex-mini.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex-mini.prompt.md
index 3cf34126e2f44..a5d40e1516560 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex-mini.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex-mini.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex.prompt.md
index b5fb7809f3f48..e4737cac501e1 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1-codex.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1.prompt.md
index 2c3011c9f5e57..6c2bf215f1499 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_1.prompt.md
@@ -765,7 +765,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -775,7 +775,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -785,6 +785,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-luna.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-luna.prompt.md
index 75162a227fa56..dc1cf943c2f06 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-luna.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-luna.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-sol.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-sol.prompt.md
index d09c2dd4d3f13..6b6d836fb329f 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-sol.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-sol.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-terra.prompt.md b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-terra.prompt.md
index 30f1d3b7ad491..bc2f1cf41f39a 100644
--- a/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-terra.prompt.md
+++ b/src/vs/platform/agentHost/test/node/e2e/providers/__snapshots__/Agent_Host_E2E___Copilot_prompts_gpt-5_6-terra.prompt.md
@@ -726,7 +726,7 @@
     },
     {
       "name": "create_session",
-      "description": "Create delegated work and start it with an initial prompt. Set `relationship` to `currentSession` when the task belongs to the current plan or deliverable; this creates a new chat that shares the current session's workspace, lifecycle, and aggregate diff. Set it to `independent` only for a separate deliverable that needs its own workspace, provider, or top-level lifecycle.",
+      "description": "Create delegated work and start it with an initial prompt, either in a new chat sharing the current session's workspace, lifecycle, and aggregate diff, or in an independent session. Only supply `worktree` when the user explicitly requests working with or without a new worktree; never combine it with `currentSession`.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -736,7 +736,7 @@
               "currentSession",
               "independent"
             ],
-            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks. Use `independent` only for a separate deliverable that needs its own workspace and top-level lifecycle."
+            "description": "Whether this work belongs to the current session or is independently managed. Use `currentSession` for tasks from the current plan or deliverable, including parallel or delegated tasks, unless the user explicitly requests a worktree. Use `independent` for a separate deliverable that needs its own workspace, provider, or top-level lifecycle, or for an explicitly requested worktree."
           },
           "prompt": {
             "type": "string",
@@ -746,6 +746,10 @@
             "type": "string",
             "description": "For `independent` work: unique project name, project/workspace URI, absolute folder path, or working directory from an existing session. Required for `independent` and invalid for `currentSession`."
           },
+          "worktree": {
+            "type": "boolean",
+            "description": "Override isolation for the new independent session. Set true only when the user explicitly asks to create a worktree, or false only when the user explicitly asks to work without one. Omit to preserve the existing isolation behavior: inherit the creating session's isolation for the same project, otherwise use worktree isolation. Only valid with relationship `independent`; omit for `currentSession`."
+          },
           "title": {
             "type": "string",
             "description": "Short title for the new chat or independent session.\n\n{maxLength: 200}"
diff --git a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
index 8e295cdd5b476..20b8d5c1fd0ab 100644
--- a/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
+++ b/src/vs/platform/agentHost/test/node/sessionServerTools.test.ts
@@ -6,6 +6,7 @@
 import assert from 'assert';
 import { DeferredPromise } from '../../../../base/common/async.js';
 import { DisposableStore } from '../../../../base/common/lifecycle.js';
+import { isWindows } from '../../../../base/common/platform.js';
 import { URI } from '../../../../base/common/uri.js';
 import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../base/test/common/utils.js';
 import { NullLogService } from '../../../log/common/log.js';
@@ -709,8 +710,9 @@ suite('SessionServerTools', () => {
 	for (const scheme of ['file', 'vscode-remote']) {
 		for (const worktree of [false, true, undefined]) {
 			test(`create_session resolves ${scheme} linked worktree roots only with worktree=false (value=${worktree})`, async () => {
-				const project = URI.from({ scheme, authority: scheme === 'file' ? '' : 'ssh-remote+example', path: '/workspace/repo' });
-				const existingWorktree = project.with({ path: '/worktrees/existing' });
+				const drive = scheme === 'file' && isWindows ? '/c:' : '';
+				const project = URI.from({ scheme, authority: scheme === 'file' ? '' : 'ssh-remote+example', path: `${drive}/workspace/repo` });
+				const existingWorktree = project.with({ path: `${drive}/worktrees/existing` });
 				let created: IAgentCreateSessionConfig | undefined;
 				const accessor = createAccessor({
 					listSessions: async () => [{

From 9c936d3cd8f73fb47970cef9e3e6fe93e5cd7a2f Mon Sep 17 00:00:00 2001
From: Sandeep Somavarapu <sasomava@microsoft.com>
Date: Wed, 9 Sep 2026 13:56:46 +0200
Subject: [PATCH 4/4] diagnostics: compare cancellation replay on base and PR

Temporary macOS A/B probe for #335076; do not merge. Alternate fixed revisions on one runner and retain host, runtime and protocol diagnostics before teardown.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .github/cancellation-ab.sh                    |  38 ++
 .github/workflows/pr.yml                      | 478 ++----------------
 .../e2e/harness/agentHostE2ETestHarness.ts    |  20 +-
 3 files changed, 97 insertions(+), 439 deletions(-)
 create mode 100644 .github/cancellation-ab.sh

diff --git a/.github/cancellation-ab.sh b/.github/cancellation-ab.sh
new file mode 100644
index 0000000000000..355f589fb987d
--- /dev/null
+++ b/.github/cancellation-ab.sh
@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Temporary investigation only; never merge this script into main.
+base=e341a3c1515af84f5f679761d76a05a02af182cd
+feature=6acb3aafa40acf016d00efd5230a97e446ecfa7e
+evidence="$RUNNER_TEMP/cancellation-ab"
+mkdir -p "$evidence"
+printf 'phase\titeration\tcommit\texit_code\n' > "$evidence/results.tsv"
+node -p 'JSON.stringify({node:process.version,platform:process.platform,arch:process.arch,copilot:require("./node_modules/@github/copilot/package.json").version})' > "$evidence/environment.json"
+sw_vers >> "$evidence/environment.json"
+failed=0
+for phase in base-1 feature-1 feature-2 base-2; do
+  if [[ "$phase" == base-* ]]; then
+    revision="$base"
+  else
+    revision="$feature"
+  fi
+  git switch --detach "$revision"
+  git apply "$RUNNER_TEMP/cancellation.patch"
+  npm run transpile-client > "$evidence/$phase-transpile.log" 2>&1
+  for iteration in 1 2 3; do
+    destination="$evidence/$phase-$iteration"
+    mkdir -p "$destination"
+    export VSCODE_CANCELLATION_DIAGNOSTICS="$destination"
+    result=0
+    ./scripts/test-integration.sh \
+      --run src/vs/platform/agentHost/test/node/e2e/providers/copilotAgentHostE2E.integrationTest.ts \
+      --grep 'cancelling a turn paused' > "$destination/test.log" 2>&1 || result=$?
+    printf '%s\t%s\t%s\t%s\n' "$phase" "$iteration" "$revision" "$result" | tee -a "$evidence/results.tsv"
+    if [[ "$result" != 0 ]]; then
+      failed=1
+    fi
+  done
+  git apply --reverse "$RUNNER_TEMP/cancellation.patch"
+done
+cat "$evidence/results.tsv" >> "$GITHUB_STEP_SUMMARY"
+exit "$failed"
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index f196afce554fb..c8aa1cb85280c 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -1,461 +1,63 @@
-name: Code OSS
+name: Cancellation A-B diagnostics (DO NOT MERGE)
 
 on:
   pull_request:
-    branches:
-      - main
-      - 'release/*'
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
+    branches: [main]
 
 permissions:
   contents: read
-  pull-requests: read
-
-env:
-  VSCODE_QUALITY: 'oss'
 
 jobs:
-  compile:
-    name: Compile & Hygiene
-    runs-on: [ self-hosted, 1ES.Pool=1es-vscode-oss-ubuntu-22.04-x64, "JobId=compile-${{ github.run_id }}-${{ github.run_number }}-${{ github.run_attempt }}" ]
+  compare:
+    if: github.head_ref == 'diagnostics/335076-cancellation-ab'
+    runs-on: macos-26-xlarge
+    timeout-minutes: 60
+    env:
+      VSCODE_QUALITY: oss
+      VSCODE_ARCH: arm64
+      NPM_ARCH: arm64
+      VSCODE_SKIP_PRELAUNCH: '1'
     steps:
-      - name: Checkout microsoft/vscode
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          fetch-depth: 0
           lfs: true
-
-      - name: Setup Node.js
-        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
         with:
           node-version-file: .nvmrc
-
-      - name: Restore node_modules cache
-        id: cache-node-modules
+      - name: Save identical diagnostic instrumentation
+        run: |
+          git diff 6acb3aafa40acf016d00efd5230a97e446ecfa7e HEAD -- src/vs/platform/agentHost/test/node/e2e/harness/agentHostE2ETestHarness.ts > "$RUNNER_TEMP/cancellation.patch"
+          git show HEAD:.github/cancellation-ab.sh > "$RUNNER_TEMP/cancellation-ab.sh"
+          git diff --exit-code e341a3c1515af84f5f679761d76a05a02af182cd 6acb3aafa40acf016d00efd5230a97e446ecfa7e -- package.json package-lock.json .npmrc .nvmrc
+      - name: Restore dependencies
+        id: cache
         uses: ./.github/actions/restore-node-modules
         with:
-          key-prefix: node_modules-compile
-          key-args: "compile $(node -p process.arch)"
-
-      - name: Install build tools
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        run: sudo apt update -y && sudo apt install -y build-essential pkg-config libx11-dev libx11-xcb-dev libxkbfile-dev libnotify-bin libkrb5-dev
-
-      - name: Install dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
+          key-prefix: node_modules-macos
+          key-args: "darwin arm64 $(node -p process.arch)"
+      - name: Install locked dependencies
+        if: steps.cache.outputs.cache-hit != 'true'
         run: |
-          set -e
-
-          for i in {1..5}; do # try 5 times
-            npm ci && break
-            if [ $i -eq 5 ]; then
-              echo "Npm install failed too many times" >&2
-              exit 1
-            fi
-            echo "Npm install failed $i, trying again..."
-          done
+          python3 -m pip install --break-system-packages setuptools
+          npm ci
         env:
-          ELECTRON_SKIP_BINARY_DOWNLOAD: 1
-          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: 1
+          npm_config_arch: arm64
+          ELECTRON_SKIP_BINARY_DOWNLOAD: '1'
+          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: '1'
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Prepare Electron types
-        run: node build/npm/electronTypes.ts
-
-      - name: Type check /build/ scripts
-        run: npm run typecheck
-        working-directory: build
-
-      - name: Prepare built-in extensions cache key
-        shell: pwsh
-        run: node build/azure-pipelines/common/computeBuiltInDepsCacheKey.ts > .build/builtindepshash
-
-      - name: Restore built-in extensions cache
-        id: cache-builtin-extensions
-        uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
-        with:
-          enableCrossOsArchive: true
-          path: .build/builtInExtensions
-          key: "builtin-extensions-${{ hashFiles('.build/builtindepshash') }}"
-
-      - name: Download built-in extensions
-        if: steps.cache-builtin-extensions.outputs.cache-hit != 'true'
-        run: node build/lib/builtInExtensions.ts
+          GYP_DEFINES: kerberos_use_rtld=false
+      - name: Prepare Electron
+        run: npm run electron -- arm64
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Check Markdown editor manifests
-        run: |
-          npm run markdown-editor-package-json-check
-          npm --prefix extensions/markdown-language-features run test-markdown-editor-package-json
-
-      - name: Compile & Hygiene
-        run: npm exec -- npm-run-all2 -lp core-ci hygiene eslint valid-layers-check define-class-fields-check vscode-dts-compile-check tsec-compile-check test-build-scripts
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-      - name: Check Codex protocol client is in sync
-        run: |
-          git fetch --no-tags --depth=1 origin "$CODEX_SYNC_BASE" || true
-          node build/codex/check-protocol-sync.ts --if-changed --base "$CODEX_SYNC_BASE"
-        env:
-          CODEX_SYNC_BASE: ${{ github.event.pull_request.base.sha }}
-
-      - name: Check cyclic dependencies
-        run: node build/lib/checkCyclicDependencies.ts out-build
-
-  linux-cli-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-cli-test.yml
-    with:
-      job_name: CLI
-      rustup_toolchain: 1.88
-
-  linux-electron-unit-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-test.yml
-    with:
-      job_name: Electron-Unit
-      electron_tests: true
-      integration_tests: false
-      smoke_tests: false
-
-  linux-electron-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-test.yml
-    with:
-      job_name: Electron
-      electron_tests: true
-      unit_tests: false
-      smoke_tests: false
-
-  linux-electron-smoke-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-test.yml
-    with:
-      job_name: Electron-Smoke
-      electron_tests: true
-      unit_tests: false
-      integration_tests: false
-
-  linux-browser-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-test.yml
-    with:
-      job_name: Browser
-      browser_tests: true
-
-  linux-remote-tests:
-    name: Linux
-    uses: ./.github/workflows/pr-linux-test.yml
-    with:
-      job_name: Remote
-      remote_tests: true
-
-  macos-electron-unit-tests:
-    name: macOS
-    uses: ./.github/workflows/pr-darwin-test.yml
-    with:
-      job_name: Electron-Unit
-      electron_tests: true
-      integration_tests: false
-      smoke_tests: false
-
-  macos-electron-tests:
-    name: macOS
-    uses: ./.github/workflows/pr-darwin-test.yml
-    with:
-      job_name: Electron
-      electron_tests: true
-      unit_tests: false
-      smoke_tests: false
-
-  macos-electron-smoke-tests:
-    name: macOS
-    uses: ./.github/workflows/pr-darwin-test.yml
-    with:
-      job_name: Electron-Smoke
-      electron_tests: true
-      unit_tests: false
-      integration_tests: false
-
-  macos-browser-tests:
-    name: macOS
-    uses: ./.github/workflows/pr-darwin-test.yml
-    with:
-      job_name: Browser
-      browser_tests: true
-
-  macos-remote-tests:
-    name: macOS
-    uses: ./.github/workflows/pr-darwin-test.yml
-    with:
-      job_name: Remote
-      remote_tests: true
-
-  windows-electron-unit-tests:
-    name: Windows
-    uses: ./.github/workflows/pr-win32-test.yml
-    with:
-      job_name: Electron-Unit
-      electron_tests: true
-      integration_tests: false
-      smoke_tests: false
-
-  windows-electron-tests:
-    name: Windows
-    uses: ./.github/workflows/pr-win32-test.yml
-    with:
-      job_name: Electron
-      electron_tests: true
-      unit_tests: false
-      smoke_tests: false
-
-  windows-electron-smoke-tests:
-    name: Windows
-    uses: ./.github/workflows/pr-win32-test.yml
-    with:
-      job_name: Electron-Smoke
-      electron_tests: true
-      unit_tests: false
-      integration_tests: false
-
-  windows-browser-tests:
-    name: Windows
-    uses: ./.github/workflows/pr-win32-test.yml
-    with:
-      job_name: Browser
-      browser_tests: true
-
-  windows-remote-tests:
-    name: Windows
-    uses: ./.github/workflows/pr-win32-test.yml
-    with:
-      job_name: Remote
-      remote_tests: true
-
-  copilot-check-test-cache:
-    name: Copilot - Check Test Cache
-    runs-on: [ self-hosted, 1ES.Pool=1es-vscode-oss-ubuntu-22.04-x64, "JobId=copilot-check-test-cache-${{ github.run_id }}-${{ github.run_number }}-${{ github.run_attempt }}" ]
-    permissions:
-      contents: read
-      pull-requests: read
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          lfs: true
-
-      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
-        with:
-          node-version-file: extensions/copilot/.nvmrc
-
-      - name: Restore node_modules cache
-        id: cache-node-modules
-        uses: ./.github/actions/restore-node-modules
-        with:
-          key-prefix: copilot-node_modules-linux
-          key-args: "$(node -p process.platform) $(node -p process.arch)"
-
-      - name: Install root dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        run: npm ci --ignore-scripts --no-workspaces
-
-      - name: Install copilot dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        working-directory: extensions/copilot
-        run: npm ci
-
-      - name: Ensure no duplicate cache keys
-        working-directory: extensions/copilot
-        run: npx tsx test/base/cache-cli check
-
-      - name: Ensure no untrusted cache changes
-        if: github.event_name == 'pull_request'
-        working-directory: extensions/copilot
-        run: npx tsx build/pr-check-cache-files.ts
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          REPOSITORY: ${{ github.repository }}
-          PULL_REQUEST: ${{ github.event.pull_request.number }}
-
-  copilot-check-telemetry:
-    name: Copilot - Check Telemetry
-    runs-on: [ self-hosted, 1ES.Pool=1es-vscode-oss-ubuntu-22.04-x64, "JobId=copilot-check-telemetry-${{ github.run_id }}-${{ github.run_number }}-${{ github.run_attempt }}" ]
-    permissions:
-      contents: read
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          lfs: true
-
-      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
-        with:
-          node-version-file: extensions/copilot/.nvmrc
-
-      - name: Validate telemetry events
-        working-directory: extensions/copilot
-        run: npx --package=@vscode/telemetry-extractor@1.20.4 --yes vscode-telemetry-extractor -s . > /dev/null
-
-  copilot-linux-tests:
-    name: Copilot - Test (Linux)
-    runs-on: [ self-hosted, 1ES.Pool=1es-vscode-oss-ubuntu-22.04-x64, "JobId=copilot-linux-tests-${{ github.run_id }}-${{ github.run_number }}-${{ github.run_attempt }}" ]
-    permissions:
-      contents: read
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          lfs: true
-
-      - name: Setup Node.js
-        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
-        with:
-          node-version-file: extensions/copilot/.nvmrc
-
-      - name: Setup Python
-        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
-        with:
-          python-version: '3.12'
-          architecture: 'x64'
-
-      - name: Setup .NET
-        uses: actions/setup-dotnet@a98b56852c35b8e3190ac28c8c2271da59106c68 # v6.0.0
-        with:
-          dotnet-version: '10.0'
-
-      - name: Install setuptools
-        run: pip install setuptools
-
-      - name: Install system dependencies
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y xvfb libgtk-3-0 libgbm1
-
-      - name: Restore node_modules cache
-        id: cache-node-modules
-        uses: ./.github/actions/restore-node-modules
-        with:
-          key-prefix: copilot-node_modules-linux
-          key-args: "$(node -p process.platform) $(node -p process.arch)"
-
-      - name: Install root dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        run: npm ci --ignore-scripts --no-workspaces
-
-      - name: Install copilot dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        working-directory: extensions/copilot
-        run: npm ci
-
-      - name: TypeScript type checking
-        working-directory: extensions/copilot
-        run: npm run typecheck
-
-      - name: Lint
-        working-directory: extensions/copilot
-        run: npm run lint
-
-      - name: Compile
-        working-directory: extensions/copilot
-        run: npm run compile
-
-      - name: Run vitest unit tests
-        working-directory: extensions/copilot
-        run: npm run test:unit
-
-      - name: Run simulation tests with cache
-        working-directory: extensions/copilot
-        run: npm run simulate-ci
-
-      - name: Run Completions Core prompt tests
-        working-directory: extensions/copilot
-        run: npm run test:prompt
-
-      - name: Run Completions Core lib tests using VS Code
-        working-directory: extensions/copilot
-        run: xvfb-run -a npm run test:completions-core
-
-      - name: Archive simulation output
-        if: always()
-        working-directory: extensions/copilot
-        run: |
-          set -e
-          mkdir -p .simulation-archive
-          tar -czf .simulation-archive/simulation.tgz -C .simulation .
-
-      - name: Upload simulation output
+      - name: Alternate base and PR on the same runner
+        run: bash "$RUNNER_TEMP/cancellation-ab.sh"
+      - name: Upload comparison evidence
         if: always()
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
-          name: copilot-simulation-output-linux-${{ github.run_attempt }}
-          path: extensions/copilot/.simulation-archive/simulation.tgz
-
-  copilot-windows-tests:
-    name: Copilot - Test (Windows)
-    runs-on: [ self-hosted, 1ES.Pool=1es-vscode-oss-windows-2022-x64, "JobId=copilot-windows-tests-${{ github.run_id }}-${{ github.run_number }}-${{ github.run_attempt }}" ]
-    permissions:
-      contents: read
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          lfs: true
-
-      - name: Setup Node.js
-        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
-        with:
-          node-version-file: extensions/copilot/.nvmrc
-
-      - name: Setup Python
-        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
-        with:
-          python-version: '3.12'
-          architecture: 'x64'
-
-      - name: Setup .NET
-        uses: actions/setup-dotnet@a98b56852c35b8e3190ac28c8c2271da59106c68 # v6.0.0
-        with:
-          dotnet-version: '10.0'
-
-      - name: Install setuptools
-        run: pip install setuptools
-
-      - name: Restore node_modules cache
-        id: cache-node-modules
-        uses: ./.github/actions/restore-node-modules
-        with:
-          key-prefix: copilot-node_modules-windows
-          key-args: "$(node -p process.platform) $(node -p process.arch)"
-
-      - name: Install root dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        run: npm ci --ignore-scripts --no-workspaces
-
-      - name: Install copilot dependencies
-        if: steps.cache-node-modules.outputs.cache-hit != 'true'
-        working-directory: extensions/copilot
-        run: npm ci
-
-      - name: Compile
-        working-directory: extensions/copilot
-        run: npm run compile
-
-      - name: Run vitest unit tests
-        working-directory: extensions/copilot
-        run: npm run test:unit
-
-      - name: Run simulation tests with cache
-        working-directory: extensions/copilot
-        run: npm run simulate-ci
-
-      - name: Run Completions Core prompt tests
-        working-directory: extensions/copilot
-        run: npm run test:prompt
-
-      - name: Run Completions Core lib tests using VS Code
-        working-directory: extensions/copilot
-        run: npm run test:completions-core
+          name: cancellation-ab-evidence
+          path: ${{ runner.temp }}/cancellation-ab
+          retention-days: 7
diff --git a/src/vs/platform/agentHost/test/node/e2e/harness/agentHostE2ETestHarness.ts b/src/vs/platform/agentHost/test/node/e2e/harness/agentHostE2ETestHarness.ts
index ad12e5ba70d38..03066db11298a 100644
--- a/src/vs/platform/agentHost/test/node/e2e/harness/agentHostE2ETestHarness.ts
+++ b/src/vs/platform/agentHost/test/node/e2e/harness/agentHostE2ETestHarness.ts
@@ -9,7 +9,7 @@
 
 import assert from 'assert';
 import { execSync } from 'child_process';
-import { chmodSync, mkdirSync, mkdtempSync, readdirSync, readFileSync, realpathSync, rmSync, statSync } from 'fs';
+import { chmodSync, cpSync, existsSync, mkdirSync, mkdtempSync, readdirSync, readFileSync, realpathSync, rmSync, statSync, writeFileSync } from 'fs';
 import { homedir, tmpdir, userInfo } from 'os';
 import { fileURLToPath } from 'url';
 import { timeout } from '../../../../../../base/common/async.js';
@@ -1120,6 +1120,24 @@ export class AgentHostE2EServerLease {
 	 * would only obscure it.
 	 */
 	async release(createdSessions: string[], forceRestart = false): Promise<void> {
+		const diagnosticRoot = process.env['VSCODE_CANCELLATION_DIAGNOSTICS'];
+		if (diagnosticRoot) {
+			const destination = mkdtempSync(join(diagnosticRoot, 'test-'));
+			writeFileSync(join(destination, 'state.json'), JSON.stringify({
+				createdSessions,
+				forceRestart,
+				notifications: this._client?.receivedNotifications(() => true),
+				capturedAt: new Date().toISOString(),
+			}, null, 2));
+			for (const [name, source] of [
+				['host', join(this._startOptions.userDataDir, 'logs')],
+				['runtime', join(this._startOptions.homeDir, '.copilot', 'logs')],
+			]) {
+				if (existsSync(source)) {
+					cpSync(source, join(destination, name), { recursive: true });
+				}
+			}
+		}
 		const client = this._client;
 		const cleanupErrors: Error[] = [];
 		if (client) {