fix: bind stdio to its configured agent

packages/ui/stdio-agent/README.md

@@ -32,7 +32,7 @@ The leaf `cordis.yml` supplies only the **swappable backends** — an LLM adapte
 | `welcome` | `ready.` | the stdin-chat banner |
 | `resumeSessionId` | — | resume a persisted session id instead of starting fresh (sourced from an env var in the leaf) |
 
-Fresh stdio sessions use the process launch directory as `session.header.cwd` and mint one combined `main-session-<uuid>` agent/session id, so durable restarts cannot collide. The UI's `main` text is a display label, not a second routing id. Resumed sessions register under the exact `resumeSessionId` and keep the cwd stored in the persisted session header.
+Fresh stdio sessions use the process launch directory as `session.header.cwd` and mint one combined `main-session-<uuid>` agent/session id, so durable restarts cannot collide. The UI's `main` text is a display label, not a second routing id; the UI binds to that fresh-id namespace, or to the exact `resumeSessionId` for a resumed run, and never selects unrelated registry roots. Resumed sessions keep the cwd stored in the persisted session header.
 
 ## The bin
 

packages/ui/stdio-agent/src/index.ts

@@ -124,5 +124,8 @@ export function apply(ctx: Context, config: Config): void {
   ctx.plugin(SessionPersistenceJsonl, { root: config.persistenceRoot ?? './.sessions' })
   ctx.plugin(UserInteractionService)
   ctx.plugin(toolAskUser)
-  ctx.plugin(uiStdio, { welcome: config.welcome ?? 'ready.' })
+  ctx.plugin(uiStdio, {
+    welcome: config.welcome ?? 'ready.',
+    ...config.resumeSessionId !== undefined ? { resumeSessionId: config.resumeSessionId } : {},
+  })
 }

packages/ui/stdio-agent/src/stdio-chat.ts

@@ -36,10 +36,13 @@ export const inject = ['agents', 'userInteraction']
 export interface Config {
   /** Banner printed once on start, before the first `> ` prompt. */
   welcome?: string
+  /** Exact persisted session id the app configured for resume; absent selects the app's fresh `main-session-*` identity. */
+  resumeSessionId?: string
 }
 
 export const Config: z<Config> = z.object({
   welcome: z.string().default('ready.'),
+  resumeSessionId: z.string(),
 })
 
 /**
@@ -95,16 +98,25 @@ export function createStdioChat(ctx: Context, config: Config, runtime: StdioRunt
   const welcome = config.welcome ?? 'ready.'
   const { input, output, exit } = runtime
 
-  // This app owns one configured top-level agent. Hold the live object
-  // directly: its per-run id is intentionally fresh, while `main` remains only
-  // the terminal's fixed display label. Runtime creator ownership distinguishes
-  // that root from its subagents even if a child is registered after an HMR
-  // replacement. Persisted parentSession lineage is deliberately irrelevant:
-  // a resumed child session can itself be this process's configured root.
-  let target: Agent | undefined = ctx.agents.roots()[0]
-  ctx.on('agent/created', () => { target ??= ctx.agents.roots()[0] })
+  // Bind only to this app's configured top-level agent. Fresh runs own the
+  // `main-session-*` namespace; resumed runs own the exact persisted id. The
+  // registry's runtime-root relation excludes subagents without confusing it
+  // with durable parentSession lineage. Keeping the matching candidates also
+  // covers HMR's publish-new-before-dispose-old ordering without ever falling
+  // through to an unrelated root owned by another app or test fixture.
+  const matchesConfiguredIdentity = (agent: Agent): boolean => config.resumeSessionId === undefined
+    ? agent.id.startsWith('main-session-')
+    : agent.id === config.resumeSessionId
+  const configuredRoots = new Set(ctx.agents.roots().filter(matchesConfiguredIdentity))
+  let target: Agent | undefined = [...configuredRoots].at(-1)
+  ctx.on('agent/created', (agent) => {
+    if (!matchesConfiguredIdentity(agent) || !ctx.agents.roots().includes(agent)) return
+    configuredRoots.add(agent)
+    target ??= agent
+  })
   ctx.on('agent/disposed', (agent) => {
-    if (target === agent) target = ctx.agents.roots().at(-1)
+    configuredRoots.delete(agent)
+    if (target === agent) target = [...configuredRoots].at(-1)
   })
 
   // Transcript rendering off the durable `session/event` feed — the assistant

packages/ui/stdio-agent/tests/stdio-chat.spec.ts

@@ -74,7 +74,7 @@ function chunkEvent(chunk: StreamChunk): SessionEvent {
   return { type: 'assistant/chunk', seq: 0, time: 0, data: { turn: 1, step: 0, chunk } }
 }
 
-const CONFIG: Config = { welcome: 'hi there' }
+const CONFIG: Config = { welcome: 'hi there', resumeSessionId: 'main' }
 
 async function setup(config: Config = CONFIG, runtimeOver: Partial<StdioRuntime> = {}) {
   const ctx = new Context()
@@ -199,7 +199,9 @@ describe('createStdioChat rendering', () => {
   })
 
   it('accepts a lineage-bearing configured agent created after the UI installs', async () => {
-    const { ctx, input } = await setup()
+    const { ctx, input } = await setup({ welcome: 'hi there', resumeSessionId: 'resumed' })
+    const unrelated = makeAgent('unrelated')
+    ctx.agents.register(unrelated)
     const resumed = makeAgent('resumed')
     ;(resumed.session.header as { parentSession?: string }).parentSession = 'persisted-parent'
     ctx.agents.register(resumed)
@@ -207,6 +209,7 @@ describe('createStdioChat rendering', () => {
     input.feed('continue')
     await new Promise(resolve => setImmediate(resolve))
 
+    expect(unrelated.sent).toEqual([])
     expect(resumed.sent).toEqual([[{ type: 'text', text: 'continue' }]])
   })
 
@@ -235,7 +238,7 @@ describe('createStdioChat rendering', () => {
 
   it('keeps the target when a different agent is disposed', async () => {
     const { ctx, out } = await setup()
-    const target = makeAgent('target')
+    const target = makeAgent('main')
     ctx.agents.register(target)
     ctx.emit('agent/disposed', makeAgent('other'))
     ctx.emit('session/event', target.session, {
@@ -245,11 +248,11 @@ describe('createStdioChat rendering', () => {
   })
 
   it('retargets a surviving root when HMR publishes it before disposing the old root', async () => {
-    const { ctx, input } = await setup()
-    const oldRoot = makeAgent('old-root')
+    const { ctx, input } = await setup({ welcome: 'hi there' })
+    const oldRoot = makeAgent('main-session-old')
     const child = makeAgent('child')
     ;(child.session.header as { parentSession?: string }).parentSession = oldRoot.id
-    const replacement = makeAgent('replacement')
+    const replacement = makeAgent('main-session-replacement')
     const lateChild = makeAgent('late-child')
     const disposeOld = ctx.agents.register(oldRoot)
     const disposeChild = ctx.agents.enter(child, oldRoot)
@@ -273,6 +276,22 @@ describe('createStdioChat rendering', () => {
     disposeChild()
   })
 
+  it('does not retarget stdin to an unrelated root after the configured agent is disposed', async () => {
+    const { ctx, input } = await setup()
+    const unrelated = makeAgent('unrelated')
+    ctx.agents.register(unrelated)
+    const configured = makeAgent('main')
+    const disposeConfigured = ctx.agents.register(configured)
+    const error = vi.spyOn(ctx.logger, 'error').mockImplementation(() => {})
+
+    disposeConfigured()
+    input.feed('must not leak')
+    await new Promise(resolve => setImmediate(resolve))
+
+    expect(unrelated.sent).toEqual([])
+    expect(error).toHaveBeenCalledWith('ui-stdio: main agent is not running')
+  })
+
   it('renders tool/call and tool/result session events', async () => {
     const { ctx, out } = await setup()
     const session = {} as Session
@@ -720,8 +739,8 @@ describe('createStdioChat input', () => {
     expect(spy).toHaveBeenCalledWith('ui-stdio: main agent is not running')
   })
 
-  it('drives the app-owned agent without a duplicate id config', async () => {
-    const { ctx, input } = await setup({ welcome: 'w' })
+  it('drives the exact app-configured resumed session', async () => {
+    const { ctx, input } = await setup({ welcome: 'w', resumeSessionId: 'worker' })
     const agent = makeAgent('worker')
     ctx.agents.register(agent)
     input.feed('hi')