diff --git a/common/changes/@microsoft/rush/fix-warm-build-cache-writes_2026-09-24.json b/common/changes/@microsoft/rush/fix-warm-build-cache-writes_2026-09-24.json
new file mode 100644
index 0000000000..45dfef1643
--- /dev/null
+++ b/common/changes/@microsoft/rush/fix-warm-build-cache-writes_2026-09-24.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/rush",
+      "comment": "Allow operations to write build cache entries when their dependencies were not re-run because a previous iteration of a long-lived graph (such as the Rush daemon) produced a trusted result at the same state hash. Dependencies skipped by the user (e.g. `--only`) still block cache writes.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@microsoft/rush"
+}
diff --git a/libraries/rush-lib/src/logic/operations/CacheableOperationPlugin.ts b/libraries/rush-lib/src/logic/operations/CacheableOperationPlugin.ts
index 52f577b98c..c915abf8ca 100644
--- a/libraries/rush-lib/src/logic/operations/CacheableOperationPlugin.ts
+++ b/libraries/rush-lib/src/logic/operations/CacheableOperationPlugin.ts
@@ -15,7 +15,7 @@ import {
 } from '@rushstack/terminal';
 
 import { CollatedTerminalProvider } from '../../utilities/CollatedTerminalProvider';
-import { OperationStatus } from './OperationStatus';
+import { OperationStatus, SUCCESS_STATUSES } from './OperationStatus';
 import { CobuildLock, type ICobuildCompletedState } from '../cobuild/CobuildLock';
 import { OperationBuildCache } from '../buildCache/OperationBuildCache';
 import { RushConstants } from '../RushConstants';
@@ -116,7 +116,14 @@ export class CacheableOperationPlugin implements IPhasedCommandPlugin {
     } = this.#options;
 
     hooks.onGraphCreatedAsync.tap(PLUGIN_NAME, (graph: IOperationGraph, context: IOperationGraphContext) => {
-      graph.hooks.beforeDeleteResults.tap(PLUGIN_NAME, () => {
+      // The state hash at which each operation last completed successfully in an iteration of this graph
+      // in which cache writes were allowed for it (i.e. no dependency had an unknown state).
+      const trustedStateHashByOperation: Map<Operation, string> = new Map();
+
+      graph.hooks.beforeDeleteResults.tap(PLUGIN_NAME, (operations: ReadonlySet<Operation>) => {
+        for (const operation of operations) {
+          trustedStateHashByOperation.delete(operation);
+        }
         // Terminals and cobuild callbacks can retain the entire completed iteration, including other
         // projects' records. All of this scratch state is rebuilt by beforeExecuteIterationAsync.
         for (const cacheContext of this.#buildCacheContextByOperation.values()) {
@@ -564,8 +571,31 @@ export class CacheableOperationPlugin implements IPhasedCommandPlugin {
 
           switch (record.status) {
             case OperationStatus.Skipped: {
-              // Skipping means cannot guarantee integrity, so prevent cache writes in dependents.
-              blockCacheWrite = true;
+              // Skipping generally means we cannot guarantee integrity, so prevent cache writes in dependents.
+              // The exception is an operation that was not re-run because a previous iteration of this graph
+              // produced a trusted result at exactly the same state hash (e.g. a result retained by a
+              // long-lived graph such as the Rush daemon). Since the state hash of an operation covers the
+              // state hashes of all of its dependencies, a consumer's cache key fully describes this input.
+              if (
+                blockCacheWrite ||
+                record.operation.enabled === false ||
+                trustedStateHashByOperation.get(operation) !== record.getStateHash()
+              ) {
+                blockCacheWrite = true;
+                trustedStateHashByOperation.delete(operation);
+              }
+              break;
+            }
+
+            default: {
+              if (!blockCacheWrite && buildCacheContext && SUCCESS_STATUSES.has(record.status)) {
+                // The outputs of this operation were produced (or restored) in an iteration where cache
+                // writes were allowed, so they can be trusted by consumers in later iterations as long as
+                // the state hash is unchanged.
+                trustedStateHashByOperation.set(operation, record.getStateHash());
+              } else {
+                trustedStateHashByOperation.delete(operation);
+              }
               break;
             }
           }
diff --git a/libraries/rush-lib/src/logic/operations/test/CacheableOperationPlugin.test.ts b/libraries/rush-lib/src/logic/operations/test/CacheableOperationPlugin.test.ts
new file mode 100644
index 0000000000..a9b3ad395a
--- /dev/null
+++ b/libraries/rush-lib/src/logic/operations/test/CacheableOperationPlugin.test.ts
@@ -0,0 +1,303 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
+// See LICENSE in the project root for license information.
+
+jest.mock('../../../utilities/Utilities');
+jest.mock('../OperationStateFile');
+jest.mock('../ProjectLogWritable', () => {
+  const actual = jest.requireActual('../ProjectLogWritable');
+  const { TerminalWritable } = jest.requireActual('@rushstack/terminal');
+  class MockTerminalWritable extends TerminalWritable {
+    protected onWriteChunk(): void {
+      /* noop */
+    }
+    protected onClose(): void {
+      /* noop */
+    }
+  }
+  return {
+    ...actual,
+    initializeProjectLogFilesAsync: jest.fn(async () => new MockTerminalWritable())
+  };
+});
+jest.mock('../OperationMetadataManager', () => {
+  class MockOperationMetadataManager {
+    public readonly logFilenameIdentifier: string;
+    public readonly metadataFolderPath: string = '.rush/temp/operation/mock';
+    public readonly stateFile: { state: undefined } = { state: undefined };
+    public constructor({ operation }: { operation: { logFilenameIdentifier: string } }) {
+      this.logFilenameIdentifier = operation.logFilenameIdentifier;
+    }
+    public async saveAsync(): Promise<void> {
+      /* noop */
+    }
+    public async tryRestoreAsync(): Promise<void> {
+      /* noop */
+    }
+    public tryRestoreStopwatch<T>(originalStopwatch: T): T {
+      return originalStopwatch;
+    }
+  }
+  return { OperationMetadataManager: MockOperationMetadataManager };
+});
+jest.mock('../../buildCache/OperationBuildCache', () => ({
+  OperationBuildCache: { forOperation: jest.fn() }
+}));
+
+import { MockWritable, StringBufferTerminalProvider, Terminal } from '@rushstack/terminal';
+
+import type { IPhase } from '../../../api/CommandLineConfiguration';
+import type { RushConfigurationProject } from '../../../api/RushConfigurationProject';
+import type { BuildCacheConfiguration } from '../../../api/BuildCacheConfiguration';
+import type { RushProjectConfiguration } from '../../../api/RushProjectConfiguration';
+import { PhasedCommandHooks, type IOperationGraphContext } from '../../../pluginFramework/PhasedCommandHooks';
+import type { IInputsSnapshot } from '../../incremental/InputsSnapshot';
+import { OperationBuildCache } from '../../buildCache/OperationBuildCache';
+import { CacheableOperationPlugin } from '../CacheableOperationPlugin';
+import { PhasedOperationPlugin } from '../PhasedOperationPlugin';
+import { OperationGraph } from '../OperationGraph';
+import { Operation } from '../Operation';
+import { OperationStatus } from '../OperationStatus';
+import type { IOperationRunner, IOperationRunnerContext } from '../IOperationRunner';
+import type { IExecutionResult } from '../IOperationExecutionResult';
+import type { OperationExecutionRecord } from '../OperationExecutionRecord';
+
+const mockPhase: IPhase = {
+  name: 'phase',
+  allowWarningsOnSuccess: false,
+  associatedParameters: new Set(),
+  dependencies: { self: new Set(), upstream: new Set() },
+  isSynthetic: false,
+  logFilenameIdentifier: 'phase',
+  missingScriptBehavior: 'silent'
+};
+
+class CacheableMockRunner implements IOperationRunner {
+  public readonly reportTiming: boolean = true;
+  public readonly silent: boolean = false;
+  public readonly cacheable: boolean = true;
+  public readonly warningsAreAllowed: boolean = false;
+  public readonly isNoOp: boolean = false;
+  public readonly name: string;
+  readonly #executions: string[];
+
+  public constructor(name: string, executions: string[]) {
+    this.name = name;
+    this.#executions = executions;
+  }
+
+  public async executeAsync(context: IOperationRunnerContext): Promise<OperationStatus> {
+    this.#executions.push(this.name);
+    return OperationStatus.Success;
+  }
+
+  public getConfigHash(): string {
+    return 'config';
+  }
+}
+
+interface ITestGraph {
+  graph: OperationGraph;
+  operations: Map<string, Operation>;
+  localHashes: Map<string, string>;
+  executions: string[];
+  cacheWrites: string[];
+  executeAsync(): Promise<IExecutionResult>;
+}
+
+/**
+ * Creates a linear chain of cacheable operations: names[0] <- names[1] <- ... (each depends on the previous).
+ */
+async function createTestGraphAsync(names: string[]): Promise<ITestGraph> {
+  const executions: string[] = [];
+  const cacheWrites: string[] = [];
+  const localHashes: Map<string, string> = new Map();
+  const operations: Map<string, Operation> = new Map();
+  const projectConfigurations: Map<RushConfigurationProject, RushProjectConfiguration> = new Map();
+
+  let previous: Operation | undefined;
+  for (const name of names) {
+    const project: RushConfigurationProject = {
+      packageName: name,
+      projectFolder: `/repo/${name}`
+    } as unknown as RushConfigurationProject;
+    projectConfigurations.set(project, {
+      getCacheDisabledReason: () => undefined
+    } as unknown as RushProjectConfiguration);
+    const operation: Operation = new Operation({
+      runner: new CacheableMockRunner(name, executions),
+      logFilenameIdentifier: name,
+      phase: mockPhase,
+      project
+    });
+    if (previous) {
+      operation.addDependency(previous);
+    }
+    previous = operation;
+    operations.set(name, operation);
+    localHashes.set(name, `${name}-v1`);
+  }
+
+  jest.mocked(OperationBuildCache.forOperation).mockImplementation(
+    (record) =>
+      ({
+        tryRestoreFromCacheAsync: async () => false,
+        trySetCacheEntryAsync: async () => {
+          cacheWrites.push(record.operation.associatedProject.packageName);
+          return true;
+        }
+      }) as unknown as OperationBuildCache
+  );
+
+  const terminal: Terminal = new Terminal(new StringBufferTerminalProvider());
+  const hooks: PhasedCommandHooks = new PhasedCommandHooks();
+  new PhasedOperationPlugin().apply(hooks);
+  new CacheableOperationPlugin({
+    allowWarningsInSuccessfulBuild: false,
+    buildCacheConfiguration: {
+      buildCacheEnabled: true,
+      cacheWriteEnabled: true
+    } as unknown as BuildCacheConfiguration,
+    cobuildConfiguration: undefined,
+    terminal,
+    excludeAppleDoubleFiles: false,
+    useDirectFileTransfersForBuildCache: false
+  }).apply(hooks);
+
+  const graph: OperationGraph = new OperationGraph(new Set(operations.values()), {
+    quietMode: true,
+    debugMode: false,
+    parallelism: 1,
+    allowOversubscription: true,
+    destinations: [new MockWritable()],
+    abortController: new AbortController()
+  });
+  await hooks.onGraphCreatedAsync.promise(graph, {
+    isIncrementalBuildAllowed: true,
+    projectConfigurations
+  } as unknown as IOperationGraphContext);
+
+  const inputsSnapshot: IInputsSnapshot = {
+    hashes: new Map(),
+    rootDirectory: '/repo',
+    hasUncommittedChanges: false,
+    getTrackedFileHashesForOperation: () => new Map(),
+    getOperationOwnStateHash: (project: RushConfigurationProject) => localHashes.get(project.packageName)!
+  };
+
+  return {
+    graph,
+    operations,
+    localHashes,
+    executions,
+    cacheWrites,
+    executeAsync: async () => {
+      executions.length = 0;
+      cacheWrites.length = 0;
+      return await graph.executeAsync({ inputsSnapshot });
+    }
+  };
+}
+
+function getStatus(testGraph: ITestGraph, result: IExecutionResult, name: string): OperationStatus {
+  return (result.operationResults.get(testGraph.operations.get(name)!) as OperationExecutionRecord).status;
+}
+
+describe(CacheableOperationPlugin.name, () => {
+  it('writes cache entries for all operations in a cold iteration', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b']);
+
+    const result: IExecutionResult = await testGraph.executeAsync();
+
+    expect(result.status).toBe(OperationStatus.Success);
+    expect(testGraph.executions).toEqual(['a', 'b']);
+    expect(testGraph.cacheWrites).toEqual(['a', 'b']);
+  });
+
+  it('writes a cache entry for an operation whose dependencies were retained from a previous iteration', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b', 'c']);
+    await testGraph.executeAsync();
+
+    testGraph.localHashes.set('c', 'c-v2');
+    const result: IExecutionResult = await testGraph.executeAsync();
+
+    expect(result.status).toBe(OperationStatus.Success);
+    expect(getStatus(testGraph, result, 'a')).toBe(OperationStatus.Skipped);
+    expect(getStatus(testGraph, result, 'b')).toBe(OperationStatus.Skipped);
+    expect(testGraph.executions).toEqual(['c']);
+    expect(testGraph.cacheWrites).toEqual(['c']);
+  });
+
+  it('keeps allowing cache writes across several warm iterations', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b', 'c']);
+    await testGraph.executeAsync();
+
+    testGraph.localHashes.set('b', 'b-v2');
+    await testGraph.executeAsync();
+    expect(testGraph.executions).toEqual(['b', 'c']);
+    expect(testGraph.cacheWrites).toEqual(['b', 'c']);
+
+    testGraph.localHashes.set('c', 'c-v2');
+    await testGraph.executeAsync();
+    expect(testGraph.executions).toEqual(['c']);
+    expect(testGraph.cacheWrites).toEqual(['c']);
+  });
+
+  it('does not write a cache entry when a dependency was skipped by the user (e.g. --only)', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b']);
+    await testGraph.executeAsync();
+
+    testGraph.operations.get('a')!.enabled = false;
+    testGraph.localHashes.set('b', 'b-v2');
+    const result: IExecutionResult = await testGraph.executeAsync();
+
+    expect(getStatus(testGraph, result, 'a')).toBe(OperationStatus.Skipped);
+    expect(testGraph.executions).toEqual(['b']);
+    expect(testGraph.cacheWrites).toEqual([]);
+  });
+
+  it('does not write a cache entry when a dependency was never executed (cold --only)', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b']);
+    testGraph.operations.get('a')!.enabled = false;
+
+    await testGraph.executeAsync();
+
+    expect(testGraph.executions).toEqual(['b']);
+    expect(testGraph.cacheWrites).toEqual([]);
+  });
+
+  it('does not trust a retained result that was produced while one of its dependencies was skipped', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b', 'c']);
+    const a: Operation = testGraph.operations.get('a')!;
+
+    // Iteration 1: "a" is skipped by the user, so "b" and "c" execute without writing cache entries.
+    a.enabled = false;
+    await testGraph.executeAsync();
+    expect(testGraph.executions).toEqual(['b', 'c']);
+    expect(testGraph.cacheWrites).toEqual([]);
+
+    // Iteration 2: "a" executes for the first time, "b" is retained (same state hash), "c" changed.
+    a.enabled = true;
+    testGraph.localHashes.set('c', 'c-v2');
+    const result: IExecutionResult = await testGraph.executeAsync();
+
+    expect(getStatus(testGraph, result, 'b')).toBe(OperationStatus.Skipped);
+    expect(testGraph.executions).toEqual(['a', 'c']);
+    // "b" was built against an unknown "a", so "c" must not write to the cache.
+    expect(testGraph.cacheWrites).toEqual(['a']);
+  });
+
+  it('does not trust results whose state hash changed without re-execution', async () => {
+    const testGraph: ITestGraph = await createTestGraphAsync(['a', 'b', 'c']);
+    await testGraph.executeAsync();
+
+    // "b" ignores dependency changes, so it is not re-run when "a" changes, but its state hash changes.
+    testGraph.operations.get('b')!.enabled = 'ignore-dependency-changes';
+    testGraph.localHashes.set('a', 'a-v2');
+    testGraph.localHashes.set('c', 'c-v2');
+    const result: IExecutionResult = await testGraph.executeAsync();
+
+    expect(getStatus(testGraph, result, 'b')).toBe(OperationStatus.Skipped);
+    expect(testGraph.executions).toEqual(['a', 'c']);
+    expect(testGraph.cacheWrites).toEqual(['a']);
+  });
+});