[backport release/v0.20.0] fix(workspace): restore last selection after restart

apps/daemon/src/collab/active-workspace-selection.ts

@@ -1,4 +1,5 @@
 import fs from 'node:fs';
+import { randomUUID } from 'node:crypto';
 import path from 'node:path';
 
 interface ActiveWorkspaceSelectionFile {
@@ -10,6 +11,11 @@ export interface ActiveWorkspaceSelectionStore {
   snapshot(): { workspaceId: string | null; generation: number };
   set(workspaceId: string): Promise<void>;
   clear(): Promise<void>;
+  clearIf(workspaceId: string): Promise<boolean>;
+  replaceIf(
+    expectedWorkspaceId: string | null,
+    workspaceId: string,
+  ): Promise<string | null>;
   subscribe(listener: (workspaceId: string | null) => void): () => void;
 }
 
@@ -53,6 +59,7 @@ export function createActiveWorkspaceSelectionStore(
   const filePath = path.join(dataDir, 'workspace-selection.json');
   let cached: string | null | undefined;
   let generation = 0;
+  let mutationTail = Promise.resolve();
   const listeners = new Set<(workspaceId: string | null) => void>();
 
   const read = (): string | null => {
@@ -79,6 +86,37 @@ export function createActiveWorkspaceSelectionStore(
     }
   };
 
+  const enqueueMutation = <T>(mutation: () => Promise<T>): Promise<T> => {
+    const result = mutationTail.then(mutation);
+    mutationTail = result.then(
+      () => undefined,
+      () => undefined,
+    );
+    return result;
+  };
+
+  const persist = async (workspaceId: string) => {
+    await fs.promises.mkdir(path.dirname(filePath), { recursive: true });
+    const tempPath = `${filePath}.${process.pid}.${randomUUID()}.tmp`;
+    try {
+      await fs.promises.writeFile(
+        tempPath,
+        JSON.stringify({ workspaceId }, null, 2),
+        'utf8',
+      );
+      await fs.promises.rename(tempPath, filePath);
+    } catch (error) {
+      await fs.promises.rm(tempPath, { force: true }).catch(() => undefined);
+      throw error;
+    }
+  };
+
+  const commit = (workspaceId: string) => {
+    cached = workspaceId;
+    generation += 1;
+    notify(workspaceId);
+  };
+
   return {
     get: read,
     snapshot() {
@@ -87,21 +125,47 @@ export function createActiveWorkspaceSelectionStore(
     async set(workspaceId: string) {
       const next = workspaceId.trim();
       if (!next) throw new Error('workspaceId is required');
-      cached = next;
-      generation += 1;
-      await fs.promises.mkdir(path.dirname(filePath), { recursive: true });
-      await fs.promises.writeFile(
-        filePath,
-        JSON.stringify({ workspaceId: next }, null, 2),
-        'utf8',
-      );
-      notify(next);
+      await enqueueMutation(async () => {
+        await persist(next);
+        commit(next);
+      });
     },
     async clear() {
-      cached = null;
-      generation += 1;
-      await fs.promises.rm(filePath, { force: true });
-      notify(null);
+      await enqueueMutation(async () => {
+        await fs.promises.rm(filePath, { force: true });
+        cached = null;
+        generation += 1;
+        notify(null);
+      });
+    },
+    async clearIf(workspaceId: string) {
+      const expected = workspaceId.trim();
+      if (!expected) return false;
+      return enqueueMutation(async () => {
+        if (read() !== expected) return false;
+        await fs.promises.rm(filePath, { force: true });
+        cached = null;
+        generation += 1;
+        notify(null);
+        return true;
+      });
+    },
+    async replaceIf(expectedWorkspaceId: string | null, workspaceId: string) {
+      const expected = expectedWorkspaceId?.trim() || null;
+      const next = workspaceId.trim();
+      if (!next) throw new Error('workspaceId is required');
+      await enqueueMutation(async () => {
+        if (read() !== expected) return;
+        await persist(next);
+        commit(next);
+      });
+
+      // A user switch can queue while the conditional write is in flight.
+      // Drain mutations that were already queued when this write settled, then
+      // report the selection that actually won instead of the temporary value.
+      const queuedThroughCommit = mutationTail;
+      await queuedThroughCommit;
+      return read();
     },
     subscribe(listener) {
       listeners.add(listener);