Keep completed tasks terminal

src/tools/taskStatusPolicy.ts

@@ -0,0 +1,4 @@
+/** Worker-facing task completion is terminal and cannot move backwards. */
+export function isTerminalTaskTransition(current: unknown, requested: string): boolean {
+  return current === "Done" && requested !== "Done";
+}

src/tools/updateTaskStatus.ts

@@ -33,6 +33,7 @@ import { db } from "../firestore.js";
 import { logActivity } from "../activityEvents.js";
 import type { Tool } from "./types.js";
 import { redactClaimTokens } from "./outputSanitizer.js";
+import { isTerminalTaskTransition } from "./taskStatusPolicy.js";
 
 const ProofSchema = z
   .object({
@@ -103,10 +104,7 @@ export const updateTaskStatus: Tool<typeof InputSchema> = {
     // unbounded loop that burns LLM tokens for no new output. Treat re-opening
     // a Done task as a no-op success so the agent moves on instead of churning.
     const current = data.status;
-    if (
-      current === "Done" &&
-      (args.status === "In progress" || args.status === "Backlog")
-    ) {
+    if (isTerminalTaskTransition(current, args.status)) {
       return {
         ok: true,
         data: { taskId: args.taskId, status: "Done" },

tests/task-status.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+
+import { isTerminalTaskTransition } from "../src/tools/taskStatusPolicy.js";
+
+describe("isTerminalTaskTransition", () => {
+  it.each(["Backlog", "In progress", "Review"])(
+    "blocks Done → %s",
+    (requested) => {
+      expect(isTerminalTaskTransition("Done", requested)).toBe(true);
+    },
+  );
+
+  it("allows idempotent completion and normal forward movement", () => {
+    expect(isTerminalTaskTransition("Done", "Done")).toBe(false);
+    expect(isTerminalTaskTransition("In progress", "Done")).toBe(false);
+  });
+});