feat(FN-5060): complete Step 2 — stabilize shared dedup guard exports

Fusion-Task-Id: FN-5060
Fusion-Task-Lineage: 35434cc4-583f-4e50-9ca3-c12546d220c1

packages/core/src/duplicate-guard.ts

@@ -4,7 +4,7 @@ import { computeContentFingerprint } from "./duplicate-detection.js";
 
 const DEFAULT_WINDOW_MS = 60_000;
 const MAX_WINDOW_MS = 300_000;
-const deterministicGuardLocks = new Map<string, Promise<void>>();
+export const deterministicGuardLocks = new Map<string, Promise<void>>();
 
 // Test-only compatibility hook used by dashboard deterministic-dedup route tests.
 export const __deterministicGuardLocksForTests = deterministicGuardLocks;
@@ -59,7 +59,8 @@ export async function runDeterministicDuplicateGuard(
         return { action: "duplicate", fingerprint, existing: deterministicConflict, releaseLock: noop };
       }
     } catch (error) {
-      opts?.logger?.warn("Deterministic duplicate pre-check failed; proceeding", {
+      opts?.logger?.warn("FN-5084 deterministic pre-check failed; proceeding", {
+        contentFingerprint: fingerprint,
         error: error instanceof Error ? error.message : String(error),
       });
     }
@@ -69,7 +70,16 @@ export async function runDeterministicDuplicateGuard(
   const lockKey = `${opts.lockScope}:${fingerprint}`;
   const existingLock = deterministicGuardLocks.get(lockKey);
   if (existingLock) {
-    await existingLock;
+    try {
+      await existingLock;
+    } catch (error) {
+      opts?.logger?.warn("FN-5084 deterministic lock wait failed; proceeding", {
+        lockKey,
+        contentFingerprint: fingerprint,
+        error: error instanceof Error ? error.message : String(error),
+      });
+      deterministicGuardLocks.delete(lockKey);
+    }
   }
 
   let releaseCalled = false;
@@ -98,8 +108,9 @@ export async function runDeterministicDuplicateGuard(
       return { action: "duplicate", fingerprint, existing: deterministicConflict, releaseLock };
     }
   } catch (error) {
-    opts?.logger?.warn("Deterministic duplicate pre-check failed; proceeding", {
+    opts?.logger?.warn("FN-5084 deterministic pre-check failed; proceeding", {
       lockKey,
+      contentFingerprint: fingerprint,
       error: error instanceof Error ? error.message : String(error),
     });
   }

packages/core/src/index.ts

@@ -141,6 +141,7 @@ export {
 export { getTaskDuplicateLineage } from "./duplicate-lineage.js";
 export {
   __getDeterministicGuardMutexSize,
+  deterministicGuardLocks,
   runDeterministicDuplicateGuard,
   reconcileDeterministicDuplicate,
   __deterministicGuardLocksForTests,

packages/dashboard/src/routes/register-task-workflow-routes.ts

@@ -25,6 +25,7 @@ import {
   formatRoleMismatchReason,
   getCurrentRepo,
   findDuplicateMatches,
+  deterministicGuardLocks,
   runDeterministicDuplicateGuard,
   reconcileDeterministicDuplicate,
 } from "@fusion/core";
@@ -41,6 +42,8 @@ const REVIEW_VERDICT_RE = /###\s+Verdict:\s*(APPROVE|REVISE|RETHINK|UNAVAILABLE)
 const REVIEW_STEP_RE = /^(plan|code) review Step (\d+): (APPROVE|REVISE|RETHINK|UNAVAILABLE)\b/i;
 const DUPLICATE_STOPWORDS = new Set(["a", "an", "the", "and", "or", "of", "to", "for", "in", "is", "on", "with", "fn"]);
 
+export const __fingerprintCreateLocksForTests = deterministicGuardLocks;
+
 function buildDuplicateQuery(title: string | undefined, description: string): string {
   const tokens = `${title ?? ""} ${description}`
     .toLowerCase()