diff --git a/src/vs/platform/agentHost/AGENTS.md b/src/vs/platform/agentHost/AGENTS.md
index cd9cca2028289..261d76664041b 100644
--- a/src/vs/platform/agentHost/AGENTS.md
+++ b/src/vs/platform/agentHost/AGENTS.md
@@ -180,13 +180,13 @@ For every provider, migration and discovery partition the same native catalog: m
 
 ### Server-tool creation provenance
 
-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 relationships and is applied before the initial prompt starts.
+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, 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 session, chat, and turn as immutable, provider-neutral creation provenance in the initial session summary `_meta` bag, before the session is published or its first prompt starts. The reference supports related-session placement, source identification and session-list presentation; it does not define a hierarchy, grant communication privileges, or trigger lifecycle notifications.
 
 `list_sessions` exposes a session's configured project URI separately from its primary and additional working directories. `create_session` accepts those URIs directly and can resolve a unique project display name, preferring the 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.
+An independent session inherits the creating session's host-owned 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`, 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 ad36193a7c7a5..5e61f20f3d653 100644
--- a/src/vs/platform/agentHost/node/agentService.ts
+++ b/src/vs/platform/agentHost/node/agentService.ts
@@ -1169,6 +1169,7 @@ 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 da4619964b8cc..a67869ff19972 100644
--- a/src/vs/platform/agentHost/node/agentServiceFoundation.ts
+++ b/src/vs/platform/agentHost/node/agentServiceFoundation.ts
@@ -31,6 +31,7 @@ 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 dad63d53cdf6d..ce925bb291cf0 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;
@@ -240,6 +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;
@@ -515,11 +519,15 @@ 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,
@@ -530,6 +538,7 @@ export function getCreateSessionArgs(rawArgs: unknown, sessions: readonly IAgent
 	return {
 		relationship,
 		workspace: resolveWorkspace(getRequiredString(workspace, 'workspace', SessionServerToolName.CreateSession), sessions),
+		...(worktree !== undefined ? { worktree } : {}),
 		prompt,
 		title,
 		...(model !== undefined ? { model } : {}),
@@ -817,13 +826,23 @@ 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;
 	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, workspace)) {
+		isolation = defaults.isolation;
+	}
 	const configValues = inheritedProviderConfig === undefined && isolation === undefined
 		? undefined
 		: {
@@ -831,7 +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/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 bba101369a01a..d9d0315ba172a 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 c1f18bfc804e2..2a91a9f84e4ee 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 4d651dcdc9449..ccf8b3bb4a492 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 491aece238ad4..f6652638b1ba5 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 534cf826ca35b..2fffb3a58547c 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 61c757b022d7d..3e919758fc350 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 debdcf4e5a7a4..ac71e6069014b 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 d44d7be9728c5..cc22f427d8135 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 d6cf6f1ec9614..9c8891fba4965 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
@@ -757,7 +757,7 @@
     },
     {
       "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": {
@@ -767,7 +767,7 @@
               "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",
@@ -777,6 +777,10 @@
             "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 04cf3c83df3f3..87f758c44c12d 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
@@ -789,7 +789,7 @@
     },
     {
       "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": {
@@ -799,7 +799,7 @@
               "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",
@@ -809,6 +809,10 @@
             "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 f6e3e6da07743..0396a155041e1 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 0e0ada56e4798..bf611713fecef 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
@@ -789,7 +789,7 @@
     },
     {
       "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": {
@@ -799,7 +799,7 @@
               "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",
@@ -809,6 +809,10 @@
             "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 f27bf98becf99..b795fbc0472de 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
@@ -789,7 +789,7 @@
     },
     {
       "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": {
@@ -799,7 +799,7 @@
               "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",
@@ -809,6 +809,10 @@
             "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 7a4918e265836..667d1926decbf 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 6224ae64aa092..0503649539148 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 70280204084fd..2fde01ab897ab 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
@@ -789,7 +789,7 @@
     },
     {
       "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": {
@@ -799,7 +799,7 @@
               "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",
@@ -809,6 +809,10 @@
             "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 2fc885130da71..a22ae640a205a 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 419398dc5fe75..6739faa4fb176 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 afe5f8189294b..5e3aec59abe77 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
@@ -750,7 +750,7 @@
     },
     {
       "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": {
@@ -760,7 +760,7 @@
               "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",
@@ -770,6 +770,10 @@
             "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 327df814b4126..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';
@@ -68,6 +69,7 @@ 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),
@@ -115,10 +117,11 @@ 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 +647,12 @@ 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 +707,147 @@ 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 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 () => [{
+						...sessionMeta('source', SessionStatus.Idle, existingWorktree),
+						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; },
+				});
+
+				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('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({
+				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 +1131,7 @@ 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 +1153,98 @@ 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');