Add file-based locking to state mutations to prevent concurrent write races

Parallel operations (e.g. stale review cleanup in `list`) could
clobber each other via read-modify-write on the shared state file.
Also fix spinner lifecycle in `review` and simplify empty-list output.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/commands/list.ts

@@ -30,14 +30,10 @@ export async function action(opts: { json?: boolean }) {
     } catch {}
   }
 
-  if (sessions.length === 0) {
-    if (opts.json) {
-      console.log("[]")
-    } else {
-      console.log("◆ No active sessions.")
-      if ((await vm.status()) !== "running") {
-        console.log(`\n${red}VM is not running.${reset}`)
-      }
+  if (sessions.length === 0 && !opts.json) {
+    console.log("◆ No active sessions.")
+    if ((await vm.status()) !== "running") {
+      console.log(`\n${red}VM is not running.${reset}`)
     }
     return
   }
@@ -59,13 +55,11 @@ export async function action(opts: { json?: boolean }) {
   )
   const statuses = Object.fromEntries(statusEntries)
 
-  // Self-heal stale in_review flags — re-check activity to avoid racing with a concurrent review start
-  for (const s of staleReviewSessions) {
-    const stillActive = await vm.isClaudeActive(s.worktree, s.branch)
-    if (!stillActive) {
-      await state.patchSession(root, s.branch, { in_review: false }).catch(() => {})
-    }
-  }
+  // Self-heal stale in_review flags in parallel and update in-memory objects
+  await Promise.all(staleReviewSessions.map(async (s) => {
+    await state.patchSession(root, s.branch, { in_review: false }).catch(() => {})
+    s.in_review = false
+  }))
 
   if (opts.json) {
     const withStatus = sessions.map(s => ({ ...s, status: statuses[s.branch] }))

src/commands/review.ts

@@ -74,13 +74,16 @@ Your thoughts, in brief.
     if (opts.print) {
       spin.text = "Running review…"
       const result = await vm.claude(session.worktree, { print: prompt })
+      spin.stop()
       if (result.output) process.stdout.write(result.output + "\n")
     } else {
       spin.succeed("Session ready")
       await vm.claude(session.worktree, { prompt })
     }
-  } finally {
+  } catch (e) {
     spin.stop()
+    throw e
+  } finally {
     // Clear review flag before saveChanges to minimize the race window
     await state.patchSession(root, session.branch, { in_review: false }).catch(() => {})
     // Save worktree changes only in interactive mode

src/state.ts

@@ -1,5 +1,5 @@
 import { join, dirname } from "path"
-import { readdir, rename } from "fs/promises"
+import { readdir, rename, mkdir, rmdir } from "fs/promises"
 import { homedir } from "os"
 
 export interface Session {
@@ -36,29 +36,64 @@ export async function save(repoRoot: string, state: State): Promise<void> {
   await rename(tmpPath, path)
 }
 
+const LOCK_TIMEOUT = 5000
+const LOCK_RETRY_MS = 50
+
+async function withStateLock<T>(repoRoot: string, fn: () => Promise<T>): Promise<T> {
+  const lockPath = statePath(repoRoot) + ".lock"
+  const start = Date.now()
+
+  while (true) {
+    try {
+      await mkdir(lockPath)
+      break
+    } catch (e: any) {
+      if (e.code !== "EEXIST") throw e
+      if (Date.now() - start > LOCK_TIMEOUT) {
+        // Stale lock — force acquire
+        await rmdir(lockPath).catch(() => {})
+        await mkdir(lockPath)
+        break
+      }
+      await Bun.sleep(LOCK_RETRY_MS)
+    }
+  }
+
+  try {
+    return await fn()
+  } finally {
+    await rmdir(lockPath).catch(() => {})
+  }
+}
+
 export async function getSession(repoRoot: string, branch: string): Promise<Session | undefined> {
   const state = await load(repoRoot)
   return state.sessions[branch]
 }
 
 export async function setSession(repoRoot: string, session: Session): Promise<void> {
-  const state = await load(repoRoot)
-  state.sessions[session.branch] = session
-  await save(repoRoot, state)
+  await withStateLock(repoRoot, async () => {
+    const state = await load(repoRoot)
+    state.sessions[session.branch] = session
+    await save(repoRoot, state)
+  })
 }
 
 export async function patchSession(repoRoot: string, branch: string, patch: Partial<Session>): Promise<void> {
-  const state = await load(repoRoot)
-  if (state.sessions[branch]) {
+  await withStateLock(repoRoot, async () => {
+    const state = await load(repoRoot)
+    if (!state.sessions[branch]) throw new Error(`session not found: ${branch}`)
     Object.assign(state.sessions[branch], patch)
     await save(repoRoot, state)
-  }
+  })
 }
 
 export async function removeSession(repoRoot: string, branch: string): Promise<void> {
-  const state = await load(repoRoot)
-  delete state.sessions[branch]
-  await save(repoRoot, state)
+  await withStateLock(repoRoot, async () => {
+    const state = await load(repoRoot)
+    delete state.sessions[branch]
+    await save(repoRoot, state)
+  })
 }
 
 export interface GlobalSession extends Session {