diff --git a/extensions/gentle-ai.ts b/extensions/gentle-ai.ts
index 39edf9a2e..7a18d90cd 100644
--- a/extensions/gentle-ai.ts
+++ b/extensions/gentle-ai.ts
@@ -7095,7 +7095,7 @@ function nativeOperationFailure(operation: ReviewControllerOperation | "gentle_r
 	const preservesNativeTargetStatusDiagnostic = nativeDiagnostics?.operation === NATIVE_REVIEW_OPERATION.STATUS;
 	const preservesAnswerConsentStartDiagnostic = operation === REVIEW_CONTROLLER_OPERATION.ANSWER_CONSENT && nativeDiagnostics?.operation === NATIVE_REVIEW_OPERATION.START;
 	const diagnostics = operation === REVIEW_CONTROLLER_OPERATION.START && error instanceof CandidateViewError && value.candidateViewPreNative === true
-		? error.diagnostics ?? { code: error.reason, message: "candidate view rejected before native START" }
+		? error.diagnostics ?? { code: error.reason, message: error.message }
 		: error instanceof CandidateViewError
 			? { code: error.reason, message: error.message }
 			: nativeDiagnostics?.operation === `review/${operation}` || preservesNativeTargetStatusDiagnostic || preservesAnswerConsentStartDiagnostic
diff --git a/odd/tasks/fix-2376-candidate-owner-preparation-errno-diagnostic.md b/odd/tasks/fix-2376-candidate-owner-preparation-errno-diagnostic.md
new file mode 100644
index 000000000..b2d3774dc
--- /dev/null
+++ b/odd/tasks/fix-2376-candidate-owner-preparation-errno-diagnostic.md
@@ -0,0 +1,28 @@
+# Task Breakdown: Fix #2376 Candidate Owner Preparation Errno Diagnostic
+
+**Feature:** `fix-2376-candidate-owner-preparation-errno-diagnostic`  
+**Issue:** #2376 (`gentle_review START: candidate-owner-preparation-failed drops the errno, leaving the failure undiagnosable`)  
+**Strategy:** Strict TDD, ODD workflow, Conventional Commits  
+
+---
+
+## Tasks
+
+### 1. Test (RED): Unit test for candidate owner preparation errno diagnostic
+- [x] In `tests/gentle-ai.test.ts`:
+  - Update `ordinary START reports candidate-owner preparation failure as pre-native no mutation` to throw `new CandidateViewError("candidate view owner preparation failed (EACCES)", "candidate-owner-preparation-failed")`.
+  - Assert that `result.diagnostics` preserves `message: "candidate view owner preparation failed (EACCES)"`.
+  - Evidence: Red test failure `message: 'candidate view rejected before native START'` observed before fix.
+
+### 2. Implementation (GREEN): Preserve CandidateViewError message
+- [x] In `extensions/gentle-ai.ts`:
+  - In `nativeOperationFailure`, update the pre-native `CandidateViewError` fallback from `"candidate view rejected before native START"` to `error.message`.
+  - Evidence: 123/123 tests passing in `tests/gentle-ai.test.ts`.
+
+### 3. Verification & Regressions
+- [x] Run test suite: `node --experimental-strip-types --test tests/gentle-ai.test.ts`.
+- [x] Run typecheck: `npm run typecheck` (0 diagnostics, 0 regressions).
+- [x] Evidence: 0 regressions, all tests passing.
+
+### 4. Work-Unit Commit
+- [x] Create conventional commit: `fix(review): preserve candidate-owner preparation errno in diagnostic message (#2376)`.
diff --git a/tests/gentle-ai.test.ts b/tests/gentle-ai.test.ts
index 9755f62f9..bacd8f2f7 100644
--- a/tests/gentle-ai.test.ts
+++ b/tests/gentle-ai.test.ts
@@ -1085,7 +1085,7 @@ test("ordinary START reports candidate-owner preparation failure as pre-native n
 		start: async () => { nativeStarts += 1; throw new Error("native START must not run"); },
 	} as unknown as NativeReviewCli;
 	const candidateViews = {
-		createOrReuse: () => { throw new CandidateViewError("candidate view owner preparation failed", "candidate-owner-preparation-failed"); },
+		createOrReuse: () => { throw new CandidateViewError("candidate view owner preparation failed (EACCES)", "candidate-owner-preparation-failed"); },
 	} as unknown as CandidateViewRegistry;
 	const result = await __testing.executeReviewControllerOperation(
 		{ operation: "start", input: JSON.stringify({ mode: "ordinary" }) },
@@ -1099,7 +1099,7 @@ test("ordinary START reports candidate-owner preparation failure as pre-native n
 	assert.equal(result.mutation_outcome, "none");
 	assert.deepEqual(result.diagnostics, {
 		code: "candidate-owner-preparation-failed",
-		message: "candidate view rejected before native START",
+		message: "candidate view owner preparation failed (EACCES)",
 	});
 
 	let materializationStatusCalls = 0;