fix(sdk): harden runtime lifecycle and JSON-RPC

Keep DeepSeekHarness.run() reusable, but make ownership of its lazy
runtime process explicit. Document the context-manager/close contract and
update every construction example to use a context manager so repeated runs
remain valid without encouraging leaked subprocesses.

Contain notification predicate failures at the subscription boundary. Remove
only the subscriber whose callback raised, deliver that exception through its
queue, and continue dispatching to healthy subscribers so arbitrary callback
code cannot terminate the shared reader thread or strand later requests.

Enforce one in-flight prompt per server session with an atomic activePrompt
guard. Route overlap through the existing -32603 handler-error response and
clear the guard in finally, preserving parallel prompts across sessions and
sequential reuse without changing JSON-RPC request or notification shapes.

Use StringDecoder for line framing so a UTF-8 code point split across Buffer
chunks is not corrupted. Add a queued-write flush barrier, and make memoized
shutdown await it before disposal and exit while retaining exactly-once
cleanup when shutdown calls race or flushing fails.

Cover callback isolation, same-session exclusion, cross-session concurrency,
split multibyte input, delayed writes, racing shutdown, and flush failure with
deterministic tests.

packages/ui/jsonrpc/README.md

@@ -20,4 +20,4 @@ The plugin owns the PROTOCOL-level exit: a `shutdown` request is answered first
 
 ## Wire notes
 
-`initialize.serverInfo.name` is the wire-stable `deepseek-harness-sdk-runtime` (SDK clients key on it, independent of this package's name). Persistence roots and the deployment persona come from `cordis.yml`; the wire exposes only parameters the server applies.
+`initialize.serverInfo.name` is the wire-stable `deepseek-harness-sdk-runtime` (SDK clients key on it, independent of this package's name). A session accepts at most one in-flight `session/prompt`; an overlapping prompt for the same `sessionId` fails immediately through the standard handler-error response, while other sessions remain independent and the same session can be reused after the active prompt settles. Persistence roots and the deployment persona come from `cordis.yml`; the wire exposes only parameters the server applies.

packages/ui/jsonrpc/src/index.ts

@@ -83,8 +83,9 @@ export const Config: Schema<JsonRpcConfig> = Schema.object({})
  * detaches the event subscriptions) and `transport.close()`.
  *
  * The `shutdown` request's process-exit semantics live HERE, because the
- * plugin owns the server and transport: the request is answered first
- * (`setImmediate` lets the response frame flush), then the plugin disposes its
+ * plugin owns the server and transport: the request is answered first, an
+ * explicit output-write barrier confirms the response frame flushed, then the
+ * plugin disposes its
  * OWN fiber and calls `exit(0)`. Own-fiber disposal is sufficient — the
  * request's `server.shutdown()` already brought every SDK-created agent to
  * quiescence (their session logs are flushed by the awaited agent-handle
@@ -109,24 +110,25 @@ export function apply(ctx: Context, config: JsonRpcConfig): void {
   const server = new HarnessSdkServer(ctx, transport)
 
   // The shutdown-request exit path, exactly once (a second `shutdown` frame
-  // racing the dispose must not re-enter). `exit(0)` runs even if the dispose
-  // throws — the client was already answered, so exiting is the honest outcome.
-  let exiting = false
-  const disposeAndExit = async (): Promise<void> => {
-    if (exiting) return
-    exiting = true
-    try {
-      await fiber.dispose()
-    } finally {
+  // racing the dispose shares the same task). Flush and disposal failures are
+  // settled independently: once shutdown was answered, process exit is still
+  // the honest outcome and neither failure may prevent the next teardown step.
+  let exitTask: Promise<void> | undefined
+  const disposeAndExit = (): Promise<void> => {
+    exitTask ??= (async () => {
+      await Promise.allSettled([Promise.resolve().then(() => transport.flush())])
+      await Promise.allSettled([Promise.resolve().then(() => fiber.dispose())])
       exit(0)
-    }
+    })()
+    return exitTask
   }
 
   transport.onRequest(async (method, params) => {
     const result = await server.handleRequest(method, params)
     if (method === 'shutdown') {
-      // Answer the request first (setImmediate lets the response frame
-      // flush), then dispose this plugin's fiber and exit 0 (see apply's doc).
+      // The transport writes the returned result after this handler resolves.
+      // Schedule the explicit flush barrier after that write, then dispose this
+      // plugin's fiber and exit 0 (see apply's doc).
       setImmediate(() => { void disposeAndExit() })
     }
     return result

packages/ui/jsonrpc/src/server.ts

@@ -36,7 +36,10 @@ export interface InitializeResult {
   serverInfo: { name: string; version: string }
 }
 
-/** Parameters of a `session/prompt` request (one user turn on one SDK session). */
+/**
+ * Parameters of a `session/prompt` request: one user turn on one SDK session,
+ * with at most one in flight per session.
+ */
 export interface SessionPromptParams {
   /** The SDK-side session id; an unknown id lazily creates the agent+session pair. */
   sessionId: string
@@ -53,6 +56,7 @@ export interface SessionPromptResult {
 interface SessionRecord {
   handle: AgentHandle
   lastTurnEnd: TurnEndReason | undefined
+  activePrompt: boolean
 }
 
 interface SubagentRecord {
@@ -147,22 +151,30 @@ export class HarnessSdkServer {
   /**
    * Handle `session/prompt`: get-or-create the session's agent, send the
    * content as the user message, await turn settle (quiescence), then notify
-   * `session.finished` with the settled turn's outcome.
+   * `session.finished` with the settled turn's outcome. A session accepts at
+   * most one prompt at a time; an overlapping request fails immediately while
+   * other sessions remain independent.
    * @param params - the target session id and prompt content.
    * @returns `{ accepted: true }` after the turn settled.
    */
   async prompt(params: SessionPromptParams): Promise<SessionPromptResult> {
     const rec = await this.getOrCreateSession(params.sessionId)
-    rec.lastTurnEnd = undefined
-    rec.handle.agent.send(params.contentBlocks)
-    await rec.handle.agent.whenIdle()
-    const status = this.finishedStatus(rec.lastTurnEnd)
-    this.transport.notify('session.finished', {
-      sessionId: params.sessionId,
-      status,
-      reason: rec.lastTurnEnd,
-    })
-    return { accepted: true }
+    if (rec.activePrompt) throw new Error(`session already has an active prompt: ${params.sessionId}`)
+    rec.activePrompt = true
+    try {
+      rec.lastTurnEnd = undefined
+      rec.handle.agent.send(params.contentBlocks)
+      await rec.handle.agent.whenIdle()
+      const status = this.finishedStatus(rec.lastTurnEnd)
+      this.transport.notify('session.finished', {
+        sessionId: params.sessionId,
+        status,
+        reason: rec.lastTurnEnd,
+      })
+      return { accepted: true }
+    } finally {
+      rec.activePrompt = false
+    }
   }
 
   /**
@@ -248,7 +260,7 @@ export class HarnessSdkServer {
       meta: { cwd: this.cwd },
       agentOptions: { model: this.model },
     })
-    const rec: SessionRecord = { handle, lastTurnEnd: undefined }
+    const rec: SessionRecord = { handle, lastTurnEnd: undefined, activePrompt: false }
     this.sessions.set(sessionId, rec)
     return rec
   }

packages/ui/jsonrpc/src/transport.ts

@@ -11,6 +11,7 @@
 
 import { randomUUID } from 'node:crypto'
 import type { Readable, Writable } from 'node:stream'
+import { StringDecoder } from 'node:string_decoder'
 
 type JsonRpcId = string | number
 type RequestHandler = (method: string, params: Record<string, unknown>) => Promise<unknown>
@@ -56,6 +57,7 @@ interface PendingRequest {
  */
 export class JsonRpcLineTransport implements JsonRpcTransportPeer {
   private buffer = ''
+  private readonly decoder = new StringDecoder('utf8')
   private started = false
   private requestHandler: RequestHandler | undefined
   private notificationHandler: NotificationHandler | undefined
@@ -122,8 +124,27 @@ export class JsonRpcLineTransport implements JsonRpcTransportPeer {
     this.write(params === undefined ? { jsonrpc: '2.0', method } : { jsonrpc: '2.0', method, params })
   }
 
+  /**
+   * Wait until every frame written before this call has reached the output's
+   * write callback. The empty queued write is a barrier and emits no protocol
+   * bytes.
+   * @returns a promise that settles with the output write callback.
+   */
+  flush(): Promise<void> {
+    return new Promise<void>((resolve, reject) => {
+      this.output.write('', (error) => {
+        if (error) reject(error)
+        else resolve()
+      })
+    })
+  }
+
   private readonly onData = (chunk: Buffer | string): void => {
-    this.buffer += typeof chunk === 'string' ? chunk : chunk.toString('utf8')
+    this.buffer += typeof chunk === 'string' ? chunk : this.decoder.write(chunk)
+    this.drainLines()
+  }
+
+  private drainLines(): void {
     for (;;) {
       const newline = this.buffer.indexOf('\n')
       if (newline < 0) break
@@ -139,6 +160,8 @@ export class JsonRpcLineTransport implements JsonRpcTransportPeer {
   }
 
   private readonly onInputEnd = (): void => {
+    this.buffer += this.decoder.end()
+    this.drainLines()
     this.failPending(new Error('JSON-RPC input closed'))
   }
 

packages/ui/jsonrpc/tests/plugin-apply.spec.ts

@@ -28,6 +28,7 @@ import * as jsonrpc from '../src/index.ts'
 /** One ordered observation on the plugin's outward-facing seams: a JSON-RPC frame written to `output`, or an `exit(code)` call. */
 type WireEvent =
   | { kind: 'frame'; frame: Record<string, unknown> }
+  | { kind: 'write-complete'; ids: (string | number)[] }
   | { kind: 'exit'; code: number }
 
 interface ApplyHarness {
@@ -36,6 +37,7 @@ interface ApplyHarness {
   fiber: Awaited<ReturnType<Context['plugin']>>
   /** Every output frame and exit call, in observation order — ordering assertions read this. */
   events: WireEvent[]
+  outputErrors: Error[]
   send(frame: Record<string, unknown>): void
   sendRaw(text: string): void
   frames(): Record<string, unknown>[]
@@ -65,7 +67,10 @@ async function settle(): Promise<void> {
  * server.spec recipe) and mount the jsonrpc plugin on it through the real
  * namespace mount path, with in-memory seams standing in for stdio/exit.
  */
-async function mountPlugin(storageDir: string): Promise<ApplyHarness> {
+async function mountPlugin(
+  storageDir: string,
+  options: { writeDelayMs?: number; failFlush?: boolean } = {},
+): Promise<ApplyHarness> {
   const ctx = new Context()
   await ctx.plugin(agentCore)
   await ctx.plugin(SessionPersistenceJsonl, { root: storageDir })
@@ -73,22 +78,39 @@ async function mountPlugin(storageDir: string): Promise<ApplyHarness> {
 
   const input = new PassThrough()
   const events: WireEvent[] = []
+  const outputErrors: Error[] = []
   let pendingOutput = ''
-  // A hand-rolled Writable (not a PassThrough): _write records each decoded
-  // frame synchronously, so `events` preserves the true frame-vs-exit order.
+  // A hand-rolled Writable (not a PassThrough): _write records frames on
+  // admission and write-complete only when its callback fires, so a delayed
+  // output proves exit waits for the transport's flush barrier.
   const output = new Writable({
     write(chunk: Buffer, _encoding, callback) {
+      const ids: (string | number)[] = []
       pendingOutput += chunk.toString('utf8')
       for (;;) {
         const newline = pendingOutput.indexOf('\n')
         if (newline < 0) break
         const line = pendingOutput.slice(0, newline).trim()
         pendingOutput = pendingOutput.slice(newline + 1)
-        if (line) events.push({ kind: 'frame', frame: JSON.parse(line) as Record<string, unknown> })
+        if (line) {
+          const frame = JSON.parse(line) as Record<string, unknown>
+          events.push({ kind: 'frame', frame })
+          if (typeof frame.id === 'string' || typeof frame.id === 'number') ids.push(frame.id)
+        }
       }
-      callback()
+      const complete = (): void => {
+        if (options.failFlush === true && chunk.length === 0) {
+          callback(new Error('flush callback failed'))
+          return
+        }
+        events.push({ kind: 'write-complete', ids })
+        callback()
+      }
+      if ((options.writeDelayMs ?? 0) > 0) setTimeout(complete, options.writeDelayMs)
+      else complete()
     },
   })
+  output.on('error', (error: Error) => { outputErrors.push(error) })
   const exit = (code: number): void => { events.push({ kind: 'exit', code }) }
 
   const fiber = await ctx.plugin(jsonrpc, { input, output, exit })
@@ -99,6 +121,7 @@ async function mountPlugin(storageDir: string): Promise<ApplyHarness> {
     ctx,
     fiber,
     events,
+    outputErrors,
     send: (frame) => { input.write(`${JSON.stringify(frame)}\n`) },
     sendRaw: (text) => { input.write(text) },
     frames,
@@ -199,7 +222,7 @@ describe('dsh-jsonrpc plugin apply', () => {
 
   it('answers shutdown before exiting 0 exactly once, even against a racing second shutdown', async () => {
     const storageDir = await mkdtemp(join(tmpdir(), 'dsh-jsonrpc-apply-shutdown-'))
-    const harness = await mountPlugin(storageDir)
+    const harness = await mountPlugin(storageDir, { writeDelayMs: 10 })
     try {
       // Two shutdown frames in ONE chunk: both are dispatched from the same
       // read-loop pass, so both setImmediate exit callbacks get scheduled and
@@ -211,15 +234,21 @@ describe('dsh-jsonrpc plugin apply', () => {
       await waitFor(() => harness.exits().length > 0 ? true : undefined, 'exit recorder call')
       expect(harness.exits()).toEqual([0])
 
-      // Response-then-exit ordering: both shutdown responses were flushed to
-      // output BEFORE exit(0) ran (the setImmediate in the request handler).
+      // Response-then-exit ordering: both response write callbacks and the
+      // empty flush barrier complete before exit(0), even on delayed output.
       const exitIndex = harness.events.findIndex(event => event.kind === 'exit')
       const firstResponse = harness.events.findIndex(event => event.kind === 'frame' && event.frame.id === 'sd-1')
       const secondResponse = harness.events.findIndex(event => event.kind === 'frame' && event.frame.id === 'sd-2')
+      const firstComplete = harness.events.findIndex(event => event.kind === 'write-complete' && event.ids.includes('sd-1'))
+      const secondComplete = harness.events.findIndex(event => event.kind === 'write-complete' && event.ids.includes('sd-2'))
+      const flushComplete = harness.events.findIndex(event => event.kind === 'write-complete' && event.ids.length === 0)
       expect(firstResponse).toBeGreaterThanOrEqual(0)
       expect(secondResponse).toBeGreaterThanOrEqual(0)
-      expect(exitIndex).toBeGreaterThan(firstResponse)
-      expect(exitIndex).toBeGreaterThan(secondResponse)
+      expect(firstComplete).toBeGreaterThan(firstResponse)
+      expect(secondComplete).toBeGreaterThan(secondResponse)
+      expect(flushComplete).toBeGreaterThan(firstComplete)
+      expect(flushComplete).toBeGreaterThan(secondComplete)
+      expect(exitIndex).toBeGreaterThan(flushComplete)
 
       // Idempotent: the racing second shutdown never produces a second exit.
       await settle()
@@ -236,6 +265,27 @@ describe('dsh-jsonrpc plugin apply', () => {
     }
   })
 
+  it('still disposes and exits once when the flush callback fails', async () => {
+    const storageDir = await mkdtemp(join(tmpdir(), 'dsh-jsonrpc-apply-flush-failure-'))
+    const harness = await mountPlugin(storageDir, { failFlush: true })
+    try {
+      harness.send({ jsonrpc: '2.0', id: 'sd-fail', method: 'shutdown' })
+
+      await waitFor(() => harness.exits().length > 0 ? true : undefined, 'exit after flush failure')
+      await settle()
+      expect(harness.exits()).toEqual([0])
+      expect(harness.outputErrors.map(error => error.message)).toEqual(['flush callback failed'])
+
+      const before = harness.frames().length
+      harness.send({ jsonrpc: '2.0', id: 'after-flush-failure', method: 'initialize', params: { cwd: storageDir, model: 'x' } })
+      await settle()
+      expect(harness.frames().length).toBe(before)
+    } finally {
+      await harness.dispose()
+      await rm(storageDir, { recursive: true, force: true })
+    }
+  })
+
   it('stops serving on a bare fiber dispose (HMR-style unload) without calling exit', async () => {
     const storageDir = await mkdtemp(join(tmpdir(), 'dsh-jsonrpc-apply-dispose-'))
     const harness = await mountPlugin(storageDir)

packages/ui/jsonrpc/tests/server.spec.ts

@@ -152,6 +152,57 @@ describe('HarnessSdkServer', () => {
     }
   })
 
+  it('rejects overlapping prompts for one session without serializing other sessions', async () => {
+    let releaseMain: (() => void) | undefined
+    const firstMainIdle = new Promise<void>((resolve) => { releaseMain = resolve })
+    const mainWhenIdle = vi.fn<() => Promise<void>>()
+      .mockReturnValueOnce(firstMainIdle)
+      .mockResolvedValue(undefined)
+    const mainSend = vi.fn()
+    const mainAgent = {
+      send: mainSend,
+      whenIdle: mainWhenIdle,
+    } as unknown as Agent
+    const otherSend = vi.fn()
+    const otherAgent = {
+      send: otherSend,
+      whenIdle: vi.fn(() => Promise.resolve()),
+    } as unknown as Agent
+    const mainHandle = { agent: mainAgent, dispose: vi.fn(() => Promise.resolve()) }
+    const otherHandle = { agent: otherAgent, dispose: vi.fn(() => Promise.resolve()) }
+    const create = vi.fn(async (options: { agentId: AgentId }) =>
+      String(options.agentId) === 'main' ? mainHandle : otherHandle)
+    const ctx = {
+      on: vi.fn(() => () => undefined),
+      agents: { create, get: () => undefined },
+      get: () => undefined,
+    } as unknown as Context
+    const server = new HarnessSdkServer(ctx, new FakeTransport())
+    const prompt = (sessionId: string, text: string) => server.prompt({
+      sessionId,
+      contentBlocks: [{ type: 'text', text }],
+    })
+
+    const first = prompt('main', 'first')
+    await vi.waitFor(() => { expect(mainSend).toHaveBeenCalledOnce() })
+
+    await expect(prompt('main', 'overlap')).rejects.toThrow('session already has an active prompt: main')
+    await expect(prompt('other', 'independent')).resolves.toEqual({ accepted: true })
+    releaseMain?.()
+    await expect(first).resolves.toEqual({ accepted: true })
+    await expect(prompt('main', 'sequential')).resolves.toEqual({ accepted: true })
+
+    mainWhenIdle.mockRejectedValueOnce(new Error('turn wait failed'))
+    await expect(prompt('main', 'failing')).rejects.toThrow('turn wait failed')
+    await expect(prompt('main', 'after failure')).resolves.toEqual({ accepted: true })
+
+    expect(mainSend).toHaveBeenCalledTimes(4)
+    expect(otherSend).toHaveBeenCalledOnce()
+    await server.shutdown()
+    expect(mainHandle.dispose).toHaveBeenCalledOnce()
+    expect(otherHandle.dispose).toHaveBeenCalledOnce()
+  })
+
   it('notifies the host when a child session is created with parent lineage', async () => {
     const storageDir = await mkdtemp(join(tmpdir(), 'dsh-jsonrpc-subagent-'))
     const ctx = await makeHarness(storageDir)
@@ -490,11 +541,11 @@ describe('HarnessSdkServer', () => {
       get: () => undefined,
     } as unknown as Context
     const server = new HarnessSdkServer(ctx, new FakeTransport()) as unknown as {
-      sessions: Map<string, { handle: AgentHandle; lastTurnEnd: undefined }>
+      sessions: Map<string, { handle: AgentHandle; lastTurnEnd: undefined; activePrompt: boolean }>
       shutdown(): Promise<Record<string, never>>
     }
-    server.sessions.set('first', { handle: { agent: {} as Agent, dispose: firstDispose }, lastTurnEnd: undefined })
-    server.sessions.set('second', { handle: { agent: {} as Agent, dispose: secondDispose }, lastTurnEnd: undefined })
+    server.sessions.set('first', { handle: { agent: {} as Agent, dispose: firstDispose }, lastTurnEnd: undefined, activePrompt: false })
+    server.sessions.set('second', { handle: { agent: {} as Agent, dispose: secondDispose }, lastTurnEnd: undefined, activePrompt: false })
 
     await expect(server.shutdown()).rejects.toThrow('SDK server teardown failed')
     expect(firstDispose).toHaveBeenCalledOnce()

packages/ui/jsonrpc/tests/transport.spec.ts

@@ -1,5 +1,5 @@
 import { once } from 'node:events'
-import { PassThrough } from 'node:stream'
+import { PassThrough, Writable } from 'node:stream'
 import { describe, expect, it } from 'vitest'
 import { JsonRpcLineTransport } from '../src/index.ts'
 
@@ -122,6 +122,64 @@ describe('JsonRpcLineTransport', () => {
     b.close()
   })
 
+  it('preserves multibyte UTF-8 characters split across Buffer chunks', async () => {
+    const input = new PassThrough()
+    const output = new PassThrough()
+    const transport = new JsonRpcLineTransport(input, output)
+    const notifications: Record<string, unknown>[] = []
+    transport.onNotification((method, params) => { notifications.push({ method, params }) })
+    transport.start()
+
+    const frame = Buffer.from(`${JSON.stringify({ jsonrpc: '2.0', method: 'message', params: { text: '你好' } })}\n`)
+    const character = Buffer.from('你')
+    const characterStart = frame.indexOf(character)
+    expect(characterStart).toBeGreaterThanOrEqual(0)
+    input.write(frame.subarray(0, characterStart + 1))
+    input.write(frame.subarray(characterStart + 1))
+    await new Promise(resolve => setTimeout(resolve, 10))
+
+    expect(notifications).toEqual([{ method: 'message', params: { text: '你好' } }])
+    transport.close()
+  })
+
+  it('flush waits for all earlier output writes', async () => {
+    const events: string[] = []
+    const output = new Writable({
+      write(chunk: Buffer, _encoding, callback) {
+        const label = chunk.length === 0 ? 'barrier' : 'frame'
+        events.push(`start:${label}`)
+        setTimeout(() => {
+          events.push(`finish:${label}`)
+          callback()
+        }, 5)
+      },
+    })
+    const transport = new JsonRpcLineTransport(new PassThrough(), output)
+
+    transport.notify('tick')
+    await transport.flush()
+
+    expect(events).toEqual([
+      'start:frame',
+      'finish:frame',
+      'start:barrier',
+      'finish:barrier',
+    ])
+    transport.close()
+  })
+
+  it('reports an output callback failure from flush', async () => {
+    const output = {
+      write(_chunk: string, callback?: (error?: Error) => void) {
+        callback?.(new Error('flush failed'))
+        return true
+      },
+    }
+    const transport = new JsonRpcLineTransport(new PassThrough(), output as never)
+
+    await expect(transport.flush()).rejects.toThrow('flush failed')
+  })
+
   it('rejects pending requests when the input closes', async () => {
     const { aToB, b } = transportPair()
     b.start()