fix(core): enforce agent-scoped ownership boundaries

packages/ui/acp/src/index.ts

@@ -591,17 +591,27 @@ export function apply(ctx: Context, config: AcpConfig): void {
         return Promise.resolve()
       },
 
-      newSession(params: NewSessionRequest): Promise<NewSessionResponse> {
+      async newSession(params: NewSessionRequest): Promise<NewSessionResponse> {
         assertOpen()
         validateWorkspaceParams(params)
         validateMcpServers(params)
         const sessionId = SessionId(randomUUID())
-        const handle = agents.create({
+        const handle = await agents.create({
           agentId: AgentId(sessionId),
           sessionId,
           meta: { cwd: params.cwd },
           agentOptions: agentOptions(config),
         })
+        // Creation is now asynchronous because it awaits the unpublished setup
+        // transaction. A client disconnect can therefore close this bridge
+        // after the entry check but before the handle resolves; never install a
+        // post-close record that quiesce() could not have seen.
+        /* v8 ignore next 4 -- the in-memory transport rejects the in-flight RPC
+           immediately on close; real stdio may let the handler resume */
+        if (closed) {
+          await handle.dispose()
+          throw internalError('connection closed during session/new')
+        }
         bySession.set(handle.agent, sessionId)
         sessions.set(sessionId, {
           sessionId,
@@ -611,7 +621,7 @@ export function apply(ctx: Context, config: AcpConfig): void {
           terminalEnabled: terminalOutputCap,
           inflight: undefined,
         })
-        return Promise.resolve({ sessionId })
+        return { sessionId }
       },
 
       async loadSession(params: LoadSessionRequest): Promise<LoadSessionResponse> {

packages/ui/acp/tests/dispose.spec.ts

@@ -229,10 +229,10 @@ describe('acp bridge — disposal & HMR safety', () => {
     // dispose one handle, and assert the other survives, registered and
     // queryable, with its session still in the store.
     const harness = await makeBridgeHarness({ storageDir, script: [] })
-    const handleA = harness.ctx.agents.create({
+    const handleA = await harness.ctx.agents.create({
       agentId: AgentId('sib-a'), sessionId: SessionId('sib-a'), agentOptions: { model: 'mock' },
     })
-    const handleB = harness.ctx.agents.create({
+    const handleB = await harness.ctx.agents.create({
       agentId: AgentId('sib-b'), sessionId: SessionId('sib-b'), agentOptions: { model: 'mock' },
     })
     expect(harness.ctx.agents.get(AgentId('sib-a'))).toBe(handleA.agent)
@@ -261,7 +261,7 @@ describe('acp bridge — disposal & HMR safety', () => {
     // a clean turn, dispose, and assert the session was STILL removed.
     const harness = await makeBridgeHarness({ storageDir, script: [textResponse('ok')] })
     harness.ctx.on('agent/disposed', () => { throw new Error('boom disposed listener') })
-    const handle = harness.ctx.agents.create({
+    const handle = await harness.ctx.agents.create({
       agentId: AgentId('guard-a'), sessionId: SessionId('guard-a'), agentOptions: { model: 'mock' },
     })
     handle.agent.send([{ type: 'text', text: 'go' }])
@@ -282,7 +282,7 @@ describe('acp bridge — disposal & HMR safety', () => {
     // first call's await agent.done + final flush finished. Every caller must
     // observe the same quiescence boundary.
     const harness = await makeBridgeHarness({ storageDir, script: ['hang'] })
-    const handle = harness.ctx.agents.create({
+    const handle = await harness.ctx.agents.create({
       agentId: AgentId('conc-a'), sessionId: SessionId('conc-a'), agentOptions: { model: 'mock' },
     })
     // Drive a turn that hangs in the model stream, so the loop is mid-turn when

packages/ui/acp/tests/edges.spec.ts

@@ -27,7 +27,7 @@ describe('acp bridge — demux & config edges', () => {
     await harness.client.newSession({ cwd: process.cwd(), mcpServers: [] })
     const before = harness.updates.length
 
-    const { agent: foreign } = harness.ctx.agents.create({ agentId: AgentId('foreign'), sessionId: SessionId('foreign-session'), agentOptions: { model: 'mock' } })
+    const { agent: foreign } = await harness.ctx.agents.create({ agentId: AgentId('foreign'), sessionId: SessionId('foreign-session'), agentOptions: { model: 'mock' } })
     foreign.send([{ type: 'text', text: 'hi' }])
     await foreign.whenIdle()
     await new Promise(r => setTimeout(r, 10))