feat(FN-5060): complete Step 5 — wire engine and mission dedup guard

packages/core/src/__tests__/mission-store.test.ts

@@ -1890,11 +1890,31 @@ describe("MissionStore", () => {
       expect(task!.description).toBe("Custom description for the task");
     });
 
-    it("emits feature:linked event", async () => {
+    it("links duplicate feature triage calls to the same canonical task", async () => {
       const { TaskStore } = await import("../store.js");
       const ts = new TaskStore(tmpDir, join(tmpDir, ".fusion-global-settings"), { inMemoryDb: true });
       const msWithTs = ts.getMissionStore();
 
+      const mission = msWithTs.createMission({ title: "Mission" });
+      const milestone = msWithTs.addMilestone(mission.id, { title: "Milestone" });
+      const slice = msWithTs.addSlice(milestone.id, { title: "Slice" });
+      const featureA = msWithTs.addFeature(slice.id, { title: "Feature A" });
+      const featureB = msWithTs.addFeature(slice.id, { title: "Feature B" });
+
+      const first = await msWithTs.triageFeature(featureA.id, "Same Task", "Same deterministic description");
+      const second = await msWithTs.triageFeature(featureB.id, "Same Task", "Same deterministic description");
+
+      expect(first.taskId).toBeTruthy();
+      expect(second.taskId).toBe(first.taskId);
+
+      const tasks = await ts.listTasks({ slim: true });
+      expect(tasks).toHaveLength(1);
+    });
+
+    it("emits feature:linked event", async () => {      const { TaskStore } = await import("../store.js");
+      const ts = new TaskStore(tmpDir, join(tmpDir, ".fusion-global-settings"), { inMemoryDb: true });
+      const msWithTs = ts.getMissionStore();
+
       const linkedHandler = vi.fn();
       msWithTs.on("feature:linked", linkedHandler);
 

packages/core/src/mission-store.ts

@@ -53,6 +53,7 @@ import {
   validateSnapshotEnvelope,
   type MissionHierarchySnapshot,
 } from "./shared-mesh-state.js";
+import { reconcileDeterministicDuplicate, runDeterministicDuplicateGuard } from "./duplicate-guard.js";
 // ── Constants ────────────────────────────────────────────────────────
 
 /**
@@ -3127,26 +3128,52 @@ export class MissionStore extends EventEmitter<MissionStoreEvents> {
     const milestone = slice ? this.getMilestone(slice.milestoneId) : undefined;
     const missionId = milestone?.missionId;
 
-    // Create the task
-    const task = await this.taskStore.createTask({
+    const lockScope = missionId ? `mission:${missionId}` : `mission-store:${this.db.dbPath}`;
+    const guard = await runDeterministicDuplicateGuard(this.taskStore, {
       title: taskTitle || feature.title,
       description,
-      branch: branchOptions?.branch,
-      baseBranch: branchOptions?.baseBranch,
-      ...(missionId
-        ? {
-            branchContext: {
-              groupId: `mission:${missionId}`,
-              source: "mission" as const,
-              assignmentMode: branchOptions?.assignmentMode ?? "shared",
-              inheritedBaseBranch: branchOptions?.baseBranch,
-            },
-          }
-        : {}),
-    });
+    }, { lockScope });
 
-    // Link the feature to the new task (this also updates feature status to "triaged")
-    const updated = this.linkFeatureToTask(featureId, task.id);
+    let linkedTaskId: string;
+    try {
+      if (guard.action === "duplicate" && guard.existing) {
+        linkedTaskId = guard.existing.id;
+      } else {
+        const createdTask = await this.taskStore.createTask({
+          title: taskTitle || feature.title,
+          description,
+          branch: branchOptions?.branch,
+          baseBranch: branchOptions?.baseBranch,
+          ...(missionId
+            ? {
+                branchContext: {
+                  groupId: `mission:${missionId}`,
+                  source: "mission" as const,
+                  assignmentMode: branchOptions?.assignmentMode ?? "shared",
+                  inheritedBaseBranch: branchOptions?.baseBranch,
+                },
+              }
+            : {}),
+        });
+
+        if (guard.fingerprint) {
+          await this.taskStore.updateTask(createdTask.id, {
+            sourceMetadataPatch: { contentFingerprint: guard.fingerprint },
+          });
+        }
+
+        const reconcile = await reconcileDeterministicDuplicate(this.taskStore, {
+          createdTask,
+          fingerprint: guard.fingerprint,
+        });
+        linkedTaskId = reconcile.canonical.id;
+      }
+    } finally {
+      guard.releaseLock();
+    }
+
+    // Link the feature to the task (this also updates feature status to "triaged")
+    const updated = this.linkFeatureToTask(featureId, linkedTaskId);
 
     return updated;
   }