Replace patchSession with setSession to fix concurrent state writes

The fire-and-forget patchSession calls in list could race with each
other, each reading stale state before writing. Collecting stale
branches and doing a single load-modify-save eliminates the race.
Also emits valid JSON (`[]`) when listing with --json and no sessions.

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

src/commands/list.ts

@@ -2,7 +2,7 @@ import { homedir } from "os"
 import * as git from "../git.ts"
 import * as vm from "../vm.ts"
 import * as state from "../state.ts"
-import { reset, dim, bold, green, yellow, cyan, magenta, red } from "../fmt.ts"
+import { reset, dim, green, yellow, cyan, magenta, red } from "../fmt.ts"
 
 export async function action(opts: { json?: boolean }) {
   const root = await git.repoRoot()
@@ -30,22 +30,26 @@ export async function action(opts: { json?: boolean }) {
     } catch {}
   }
 
-  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}`)
+  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}`)
+      }
     }
     return
   }
 
   // Determine status for each session in parallel
+  const staleReviewBranches: string[] = []
   const statusEntries = await Promise.all(
     sessions.map(async (s): Promise<[string, string]> => {
       const active = await vm.isClaudeActive(s.worktree, s.branch)
       if (active && s.in_review) return [s.branch, "review"]
       if (!active && s.in_review) {
-        // Self-heal stale in_review flag (fire-and-forget)
-        state.patchSession(root, s.branch, { in_review: false }).catch(() => {})
+        staleReviewBranches.push(s.branch)
         s.in_review = false
       }
       if (active) return [s.branch, "active"]
@@ -57,6 +61,15 @@ export async function action(opts: { json?: boolean }) {
   )
   const statuses = Object.fromEntries(statusEntries)
 
+  // Batch-clear stale in_review flags in a single write
+  if (staleReviewBranches.length > 0) {
+    const freshState = await state.load(root)
+    for (const branch of staleReviewBranches) {
+      if (freshState.sessions[branch]) freshState.sessions[branch].in_review = false
+    }
+    await state.save(root, freshState).catch(() => {})
+  }
+
   if (opts.json) {
     const withStatus = sessions.map(s => ({ ...s, status: statuses[s.branch] }))
     console.log(JSON.stringify(withStatus, null, 2))

src/commands/review.ts

@@ -68,13 +68,13 @@ Your thoughts, in brief.
 `
   if (extra) prompt += "\n\n" + extra
 
-  await state.patchSession(root, session.branch, { in_review: true })
+  session.in_review = true
+  await state.setSession(root, session).catch(() => {})
 
   try {
     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")
@@ -82,7 +82,8 @@ Your thoughts, in brief.
     }
   } finally {
     spin.stop()
-    await state.patchSession(root, session.branch, { in_review: false }).catch(() => {})
+    session.in_review = false
+    await state.setSession(root, session).catch(() => {})
     if (!opts.print) await saveChanges(session.worktree, session.branch).catch(() => {})
   }
 }

src/state.ts

@@ -37,27 +37,20 @@ export async function save(repoRoot: string, state: State): Promise<void> {
 }
 
 export async function getSession(repoRoot: string, branch: string): Promise<Session | undefined> {
-  const st = await load(repoRoot)
-  return st.sessions[branch]
+  const state = await load(repoRoot)
+  return state.sessions[branch]
 }
 
 export async function setSession(repoRoot: string, session: Session): Promise<void> {
-  const st = await load(repoRoot)
-  st.sessions[session.branch] = session
-  await save(repoRoot, st)
-}
-
-export async function patchSession(repoRoot: string, branch: string, patch: Partial<Session>): Promise<void> {
-  const st = await load(repoRoot)
-  if (!st.sessions[branch]) throw new Error(`session not found: ${branch}`)
-  Object.assign(st.sessions[branch], patch)
-  await save(repoRoot, st)
+  const state = await load(repoRoot)
+  state.sessions[session.branch] = session
+  await save(repoRoot, state)
 }
 
 export async function removeSession(repoRoot: string, branch: string): Promise<void> {
-  const st = await load(repoRoot)
-  delete st.sessions[branch]
-  await save(repoRoot, st)
+  const state = await load(repoRoot)
+  delete state.sessions[branch]
+  await save(repoRoot, state)
 }
 
 export interface GlobalSession extends Session {