opentui(v2): Ctrl-C stops the agent; second press (debounced) quits

Item 11 — "stopping the agent doesn't work". Ctrl+C used to immediately destroy
the renderer. Now a turn-aware state machine (opencode's double-press model, the
user's preferred behaviour):

- While a turn runs (store.info.running): first Ctrl+C → session.interrupt
  {session_id} (STOP the agent), and arms a 3s quit window with a warn hint
  "⏹ stopped — Ctrl+C again to quit".
- Idle: first Ctrl+C arms the window ("Ctrl+C again to quit"); a stray single
  press never nukes the session.
- A second Ctrl+C within the window KILLS the TUI (renderer.destroy → clean
  scope teardown → gateway child EOF).
- A blocking prompt still owns Ctrl+C (deny/cancel) — unchanged.

Wiring: renderer.ts gains an `onCtrlC` hook (owns Ctrl+C when not blocked);
entry builds the machine (gateway yielded before the renderer so it can read
`running` + send interrupt). store gains a transient `hint` slice; StatusLine
shows hint (warn, priority) or the busy face (dim).

Live-smoked: long turn → Ctrl+C shows "stopped" + idle dot; second press exits
cleanly with no orphaned gateway child (the user's installed-venv sessions
untouched). 60 pass.

ui-tui-opentui-v2/src/boundary/renderer.ts

@@ -19,6 +19,12 @@ export interface RendererOptions {
   readonly mouse: boolean
   /** When true, a blocking prompt owns Ctrl+C (cancel) — the global quit is suppressed (gotcha §8 #6). */
   readonly isBlocked?: () => boolean
+  /**
+   * Ctrl+C handler (item 11). When set, it OWNS Ctrl+C while not blocked — the
+   * entry's state machine decides interrupt-the-turn vs quit. When omitted, the
+   * default is an immediate `renderer.destroy()` (quit).
+   */
+  readonly onCtrlC?: () => void
 }
 
 /**
@@ -57,7 +63,10 @@ export const acquireRenderer = Effect.fn('Renderer.acquire')(function* (options:
   // (gotcha §8 #6) — the prompt's own handler sends the cancel reply.
   const isBlocked = options.isBlocked ?? (() => false)
   renderer.keyInput.on('keypress', (key: KeyEvent) => {
-    if (key.ctrl && key.name === 'c' && !isBlocked() && !renderer.isDestroyed) renderer.destroy()
+    if (!(key.ctrl && key.name === 'c') || renderer.isDestroyed) return
+    if (isBlocked()) return // a blocking prompt owns Ctrl+C (→ deny/cancel)
+    if (options.onCtrlC) options.onCtrlC()
+    else renderer.destroy()
   })
 
   return { renderer, shutdown } as const

ui-tui-opentui-v2/src/entry/main.tsx

@@ -49,6 +49,8 @@ export interface TuiInput {
 
 const READY_POLL = Duration.millis(100)
 const READY_TIMEOUT_MS = 20_000
+/** Window after a Ctrl+C in which a second Ctrl+C quits the TUI (item 11). */
+const QUIT_WINDOW_MS = 3_000
 
 /**
  * Resume a session INTO the store: buffer live events across the `session.resume`
@@ -137,16 +139,65 @@ export const run = Effect.fn('Tui.run')(function* (input: TuiInput) {
       // Solid side: the store + reducer. Created here, lives in Solid-land.
       const store = createSessionStore()
 
-      // A blocking prompt owns Ctrl+C (→ cancel) — suppress the global quit while one is up.
-      const { renderer, shutdown } = yield* acquireRenderer({
-        mouse: input.mouse,
-        isBlocked: () => store.state.prompt !== undefined
-      })
-
       // Contact point #2: boundary pushes decoded events into the Solid store.
       const gateway = yield* GatewayService
       yield* gateway.subscribe(event => store.apply(event))
 
+      // ── Ctrl+C state machine (item 11) ──────────────────────────────────
+      // While a turn runs, the first Ctrl+C STOPS the agent (session.interrupt);
+      // a second Ctrl+C within QUIT_WINDOW_MS (or when idle) KILLS the TUI. The
+      // debounce stops a stray Ctrl+C from nuking the session (opencode's
+      // double-press model; the user's preferred behaviour).
+      let quitArmed = false
+      let quitTimer: ReturnType<typeof setTimeout> | undefined
+      let doQuit = () => {} // assigned once the renderer exists
+      const disarmQuit = () => {
+        quitArmed = false
+        if (quitTimer) clearTimeout(quitTimer)
+        quitTimer = undefined
+        store.setHint(undefined)
+      }
+      const armQuit = (message: string) => {
+        quitArmed = true
+        store.setHint(message)
+        if (quitTimer) clearTimeout(quitTimer)
+        quitTimer = setTimeout(disarmQuit, QUIT_WINDOW_MS)
+      }
+      const interruptTurn = () => {
+        const sid = gateway.sessionId()
+        if (!sid) return
+        Effect.runFork(
+          gateway
+            .request('session.interrupt', { session_id: sid })
+            .pipe(
+              Effect.catchCause(cause => Effect.sync(() => getLog().warn('interrupt', 'failed', { cause: String(cause) })))
+            )
+        )
+      }
+      const onCtrlC = () => {
+        if (quitArmed) {
+          disarmQuit()
+          doQuit()
+          return
+        }
+        if (store.state.info.running) {
+          interruptTurn()
+          armQuit('⏹ stopped — Ctrl+C again to quit')
+        } else {
+          armQuit('Ctrl+C again to quit')
+        }
+      }
+
+      // A blocking prompt owns Ctrl+C (→ cancel); otherwise the state machine above runs.
+      const { renderer, shutdown } = yield* acquireRenderer({
+        mouse: input.mouse,
+        isBlocked: () => store.state.prompt !== undefined,
+        onCtrlC
+      })
+      doQuit = () => {
+        if (!renderer.isDestroyed) renderer.destroy()
+      }
+
       // Submit a user turn: the service value is in hand, so `gateway.request(...)`
       // is Effect<…, never> — fire it detached with runFork; failures are logged.
       const submitPrompt = (text: string) => {

ui-tui-opentui-v2/src/logic/store.ts

@@ -148,6 +148,9 @@ export interface StoreState {
   status: string | undefined
   /** Live session chrome for the status bar (model/effort/cwd/branch/context/running). */
   info: SessionInfo
+  /** Transient hint shown above the composer (e.g. "Ctrl+C again to quit" — item 11);
+   *  takes visual priority over the busy `status` face. Undefined when none. */
+  hint: string | undefined
 }
 
 const LRU_LIMIT = 1000
@@ -231,7 +234,8 @@ export function createSessionStore() {
     subagents: [],
     dashboard: false,
     status: undefined,
-    info: {}
+    info: {},
+    hint: undefined
   })
 
   // Monotonic part id (stable `key` per part so a new tool part below a streaming
@@ -364,6 +368,11 @@ export function createSessionStore() {
     setState('picker', undefined)
   }
 
+  /** Set / clear the transient composer hint ("Ctrl+C again to quit" — item 11). */
+  function setHint(text: string | undefined): void {
+    setState('hint', text)
+  }
+
   /** Merge a session-info patch into the chrome state (status bar — item 14). */
   function applyInfo(raw: { readonly [k: string]: unknown }): void {
     const patch = readInfoPatch(raw)
@@ -598,6 +607,7 @@ export function createSessionStore() {
     setCompletions,
     clearCompletions,
     applyInfo,
+    setHint,
     openDashboard,
     closeDashboard,
     hydrate,

ui-tui-opentui-v2/src/test/store.test.ts

@@ -240,6 +240,15 @@ describe('session store — session chrome / status bar (item 14)', () => {
     store.applyInfo({ branch: 'dev' }) // partial patch — model/cwd must survive
     expect(store.state.info).toMatchObject({ model: 'gpt-5.4', cwd: '/tmp', branch: 'dev' })
   })
+
+  test('setHint sets/clears the transient composer hint (Ctrl+C again to quit — item 11)', () => {
+    const store = createSessionStore()
+    expect(store.state.hint).toBeUndefined()
+    store.setHint('Ctrl+C again to quit')
+    expect(store.state.hint).toBe('Ctrl+C again to quit')
+    store.setHint(undefined)
+    expect(store.state.hint).toBeUndefined()
+  })
 })
 
 describe('session store — resume hydrate (Phase 4b)', () => {

ui-tui-opentui-v2/src/view/statusLine.tsx

@@ -1,9 +1,12 @@
 /**
- * StatusLine — the transient busy indicator (spec §3 chrome; Ink's FaceTicker).
+ * StatusLine — the transient line just below the transcript (spec §3 chrome).
- * Shows the kaomoji face/verb from `thinking.delta`/`status.update` WHILE a turn
+ * Shows EITHER:
- * runs, above the composer; cleared on `message.complete`. This keeps those
+ *   - a `hint` (e.g. "Ctrl+C again to quit" — item 11), in the warn colour and
- * transient indicators OUT of the transcript (they used to render as reasoning
+ *     taking priority; or
- * rows and linger). Themed, dim. Renders nothing when idle.
+ *   - the kaomoji busy face/verb from `thinking.delta`/`status.update` WHILE a
+ *     turn runs (Ink's FaceTicker), dim, cleared on `message.complete`.
+ * This keeps those transient indicators OUT of the transcript. Renders nothing
+ * when both are idle.
  */
 import { Show } from 'solid-js'
 
@@ -12,12 +15,14 @@ import { useTheme } from './theme.tsx'
 
 export function StatusLine(props: { store: SessionStore }) {
   const theme = useTheme()
+  const line = () => props.store.state.hint ?? props.store.state.status
+  const isHint = () => props.store.state.hint !== undefined
   return (
-    <Show when={props.store.state.status}>
+    <Show when={line()}>
-      {status => (
+      {text => (
         <box style={{ flexShrink: 0 }}>
           <text>
-            <span style={{ fg: theme().color.muted }}>{status()}</span>
+            <span style={{ fg: isHint() ? theme().color.warn : theme().color.muted }}>{text()}</span>
           </text>
         </box>
       )}