feat: Claude Agent SDK backend + clean-room PostgresSessionStore (v2.7.5)

Lands the lean-SDK direction (boocode_code_review_v2 §1 #9) behind a flag.
Adds @anthropic-ai/claude-agent-sdk@0.3.159 (Commercial Terms, runtime dep).

- PostgresSessionStore: clean-room impl of the SDK's real SessionStore type
  over a new claude_session_entries table. Typechecks against the SDK type;
  8 DB-integration tests.
- ClaudeSdkBackend (implements AgentBackend): one warm query() per (chat,claude)
  in streaming-input mode via a pushable async-iterable pump, sessionStore +
  resume continuity, pure mapSdkMessage->AgentEvent, session_id from init,
  usage/cost onto agent_sessions (backend CHECK gains 'claude_sdk').
- Routing env-gated by CLAUDE_SDK_BACKEND (default off) -> PTY path UNCHANGED.
- Built against real SDK 0.3.159 types (install paid off: partial=stream_event
  needing includePartialMessages, MessageParam, result error arm).
- Fix latent test-infra deadlock: serialize DB suites (fileParallelism:false).

Coder 269 passing default / 290 with DB; tsc clean vs SDK types; builds clean.
LIVE pump + resume + actual claude turn need a host smoke (CLAUDE_SDK_BACKEND=1
+ claude binary + auth). zod peer-dep wants ^4 (workspace 3.25). Builds on v2.7.4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/coder/src/schema.sql

@@ -261,6 +261,34 @@ CREATE TABLE IF NOT EXISTS checkpoints (
 );
 CREATE INDEX IF NOT EXISTS checkpoints_chat_created_idx ON checkpoints(chat_id, created_at);
 
+-- claude-sdk-sessionstore #9 (Part 1): append-only mirror of Claude Agent SDK
+-- session transcripts. The SDK's SessionStore adapter writes one JSONL line per
+-- entry; PostgresSessionStore (services/backends/claude-session-store.ts) inserts
+-- one row per entry and replays them ORDER BY id on resume. The store is generic
+-- per the SDK's SessionKey (project_key, session_id, subpath) — chat↔session
+-- ownership lives in agent_sessions, not here. subpath '' is the main transcript
+-- (the SDK's undefined subpath maps to '' in the column).
+CREATE TABLE IF NOT EXISTS claude_session_entries (
+  id          BIGSERIAL PRIMARY KEY,
+  project_key TEXT NOT NULL,
+  session_id  TEXT NOT NULL,
+  subpath     TEXT NOT NULL DEFAULT '',   -- '' = main transcript (SDK's undefined subpath maps here)
+  entry       JSONB NOT NULL,
+  created_at  TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp()
+);
+CREATE INDEX IF NOT EXISTS claude_session_entries_key_idx ON claude_session_entries (project_key, session_id, subpath, id);
+
+-- claude-sdk-sessionstore #9 (Part 2): the warm Claude-SDK backend persists its
+-- agent_sessions rows with backend='claude_sdk'. Widen the named CHECK to accept
+-- it. Idempotent: DROP the named constraint (the inline CREATE TABLE check above
+-- carries this explicit name, so DROP IF EXISTS targets it) + re-ADD the widened
+-- list. Re-runs/fresh deploys land on the same final constraint (the table-level
+-- CREATE already includes only the old two values on a fresh DB; this block then
+-- replaces it with the three-value list).
+ALTER TABLE agent_sessions DROP CONSTRAINT IF EXISTS agent_sessions_backend_chk;
+ALTER TABLE agent_sessions ADD CONSTRAINT agent_sessions_backend_chk
+  CHECK (backend IN ('opencode_server', 'acp_warm', 'claude_sdk'));
+
 -- LISTEN/NOTIFY fast path: every tasks INSERT (from any call site — routes,
 -- new_task tool, arena, MCP server) fires pg_notify('tasks_new') in the same
 -- transaction, so the dispatcher reacts immediately instead of waiting for the

apps/coder/src/services/agent-backend.ts

@@ -13,7 +13,7 @@ import type { AcpToolSnapshot } from './acp-tool-snapshot.js';
 import type { AgentCommand } from './provider-types.js';
 
 /** Backend transport kind. Mirrors `agent_sessions.backend` CHECK in schema.sql. */
-export type AgentBackendKind = 'opencode_server' | 'acp_warm';
+export type AgentBackendKind = 'opencode_server' | 'acp_warm' | 'claude_sdk';
 
 /**
  * Normalized, transport-agnostic events a backend emits during a turn (§2).

apps/coder/src/services/backends/__tests__/claude-sdk-map.test.ts

@@ -0,0 +1,181 @@
+import { describe, it, expect } from 'vitest';
+import type { SDKMessage } from '@anthropic-ai/claude-agent-sdk';
+import { mapSdkMessage, createClaudeSdkMapState } from '../claude-sdk-map.js';
+import type { AgentEvent } from '../../agent-backend.js';
+
+/**
+ * Pure mapper for Claude-SDK messages → AgentEvents (claude-sdk-sessionstore #9 Part 2).
+ * Verifies the partial-stream → live-delta mapping, tool assembly across blocks, and
+ * the final-assistant dedup, with no live `claude` binary involved.
+ *
+ * Messages are cast through `unknown` to `SDKMessage`: the real SDK shapes carry many
+ * fields (uuid, parent_tool_use_id, …) irrelevant to the mapper, which reads only the
+ * `type`/`event`/`message.content` it discriminates on. The cast keeps the fixtures
+ * minimal while the production code path sees the full real types (the backend's
+ * typecheck against the real SDK is the type-safety proof).
+ */
+function msg(m: unknown): SDKMessage {
+  return m as SDKMessage;
+}
+
+/** A partial-stream message wrapping one BetaRawMessageStreamEvent. */
+function streamEvent(event: unknown): SDKMessage {
+  return msg({ type: 'stream_event', event, parent_tool_use_id: null, uuid: 'u', session_id: 's' });
+}
+
+describe('mapSdkMessage — partial stream deltas', () => {
+  it('maps a text_delta to a text event', () => {
+    const state = createClaudeSdkMapState();
+    const out = mapSdkMessage(
+      streamEvent({ type: 'content_block_delta', index: 0, delta: { type: 'text_delta', text: 'Hello' } }),
+      state,
+    );
+    expect(out).toEqual<AgentEvent[]>([{ type: 'text', text: 'Hello' }]);
+  });
+
+  it('maps a thinking_delta to a reasoning event', () => {
+    const state = createClaudeSdkMapState();
+    const out = mapSdkMessage(
+      streamEvent({
+        type: 'content_block_delta',
+        index: 0,
+        delta: { type: 'thinking_delta', thinking: 'pondering', estimated_tokens: null },
+      }),
+      state,
+    );
+    expect(out).toEqual<AgentEvent[]>([{ type: 'reasoning', text: 'pondering' }]);
+  });
+
+  it('drops empty text/thinking deltas', () => {
+    const state = createClaudeSdkMapState();
+    expect(
+      mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 0, delta: { type: 'text_delta', text: '' } }), state),
+    ).toEqual([]);
+    expect(
+      mapSdkMessage(
+        streamEvent({ type: 'content_block_delta', index: 0, delta: { type: 'thinking_delta', thinking: '', estimated_tokens: null } }),
+        state,
+      ),
+    ).toEqual([]);
+  });
+
+  it('ignores message framing + signature/citation deltas', () => {
+    const state = createClaudeSdkMapState();
+    expect(mapSdkMessage(streamEvent({ type: 'message_start', message: {} }), state)).toEqual([]);
+    expect(mapSdkMessage(streamEvent({ type: 'message_stop' }), state)).toEqual([]);
+    expect(
+      mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 0, delta: { type: 'signature_delta', signature: 'x' } }), state),
+    ).toEqual([]);
+  });
+});
+
+describe('mapSdkMessage — tool assembly across blocks', () => {
+  it('opens a tool_call on content_block_start, buffers input_json_delta, emits tool_update with parsed input on stop', () => {
+    const state = createClaudeSdkMapState();
+
+    const started = mapSdkMessage(
+      streamEvent({
+        type: 'content_block_start',
+        index: 1,
+        content_block: { type: 'tool_use', id: 'tool-1', name: 'view_file', input: {} },
+      }),
+      state,
+    );
+    expect(started).toEqual<AgentEvent[]>([
+      { type: 'tool_call', toolCall: { toolCallId: 'tool-1', title: 'view_file', kind: null, status: 'in_progress', rawInput: {}, rawOutput: undefined } },
+    ]);
+
+    // args stream in fragments under the same block index
+    expect(
+      mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 1, delta: { type: 'input_json_delta', partial_json: '{"path":' } }), state),
+    ).toEqual([]);
+    expect(
+      mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 1, delta: { type: 'input_json_delta', partial_json: '"a.ts"}' } }), state),
+    ).toEqual([]);
+
+    const stopped = mapSdkMessage(streamEvent({ type: 'content_block_stop', index: 1 }), state);
+    expect(stopped).toHaveLength(1);
+    const ev = stopped[0]!;
+    expect(ev.type).toBe('tool_update');
+    if (ev.type === 'tool_update') {
+      expect(ev.toolCall.toolCallId).toBe('tool-1');
+      expect(ev.toolCall.title).toBe('view_file');
+      expect(ev.toolCall.rawInput).toEqual({ path: 'a.ts' });
+    }
+  });
+
+  it('content_block_stop for a non-tool block (no tracked index) emits nothing', () => {
+    const state = createClaudeSdkMapState();
+    // text block was streamed at index 0 but never tracked as a tool
+    mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 0, delta: { type: 'text_delta', text: 'hi' } }), state);
+    expect(mapSdkMessage(streamEvent({ type: 'content_block_stop', index: 0 }), state)).toEqual([]);
+  });
+
+  it('falls back to the prior input when the buffered tool JSON is invalid', () => {
+    const state = createClaudeSdkMapState();
+    mapSdkMessage(
+      streamEvent({ type: 'content_block_start', index: 2, content_block: { type: 'tool_use', id: 't2', name: 'grep', input: { q: 'seed' } } }),
+      state,
+    );
+    mapSdkMessage(streamEvent({ type: 'content_block_delta', index: 2, delta: { type: 'input_json_delta', partial_json: '{not json' } }), state);
+    const stopped = mapSdkMessage(streamEvent({ type: 'content_block_stop', index: 2 }), state);
+    const ev = stopped[0]!;
+    if (ev.type === 'tool_update') {
+      expect(ev.toolCall.rawInput).toEqual({ q: 'seed' });
+    } else {
+      throw new Error('expected tool_update');
+    }
+  });
+});
+
+describe('mapSdkMessage — final assistant message', () => {
+  function assistant(content: unknown[]): SDKMessage {
+    return msg({ type: 'assistant', message: { content }, parent_tool_use_id: null, uuid: 'u', session_id: 's' });
+  }
+
+  it('dedups text/thinking (already streamed) and emits a completed tool_update per tool_use block', () => {
+    const state = createClaudeSdkMapState();
+    const out = mapSdkMessage(
+      assistant([
+        { type: 'text', text: 'final answer', citations: null },
+        { type: 'thinking', thinking: 'reasoned', signature: 'sig' },
+        { type: 'tool_use', id: 'tool-9', name: 'find_files', input: { glob: '**/*.ts' } },
+      ]),
+      state,
+    );
+    expect(out).toEqual<AgentEvent[]>([
+      {
+        type: 'tool_update',
+        toolCall: { toolCallId: 'tool-9', title: 'find_files', kind: null, status: 'completed', rawInput: { glob: '**/*.ts' }, rawOutput: undefined },
+      },
+    ]);
+  });
+
+  it('preserves a title from a prior partial tool_call snapshot', () => {
+    const state = createClaudeSdkMapState();
+    mapSdkMessage(
+      streamEvent({ type: 'content_block_start', index: 0, content_block: { type: 'tool_use', id: 'tool-x', name: 'view_file', input: {} } }),
+      state,
+    );
+    const out = mapSdkMessage(assistant([{ type: 'tool_use', id: 'tool-x', name: 'view_file', input: { path: 'z' } }]), state);
+    const ev = out[0]!;
+    if (ev.type === 'tool_update') {
+      expect(ev.toolCall.status).toBe('completed');
+      expect(ev.toolCall.title).toBe('view_file');
+      expect(ev.toolCall.rawInput).toEqual({ path: 'z' });
+    } else {
+      throw new Error('expected tool_update');
+    }
+  });
+});
+
+describe('mapSdkMessage — non-content messages', () => {
+  it('returns [] for system/init, status, result, and other variants', () => {
+    const state = createClaudeSdkMapState();
+    expect(mapSdkMessage(msg({ type: 'system', subtype: 'init', session_id: 's', uuid: 'u' }), state)).toEqual([]);
+    expect(mapSdkMessage(msg({ type: 'system', subtype: 'status', status: null, session_id: 's', uuid: 'u' }), state)).toEqual([]);
+    expect(
+      mapSdkMessage(msg({ type: 'result', subtype: 'success', result: 'done', session_id: 's', uuid: 'u' }), state),
+    ).toEqual([]);
+  });
+});

apps/coder/src/services/backends/__tests__/claude-sdk-routing.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect } from 'vitest';
+import { shouldUseClaudeSdk, claudeSdkBackendEnabled } from '../claude-sdk-routing.js';
+
+/**
+ * Env-flagged routing for the warm Claude-SDK backend. With CLAUDE_SDK_BACKEND off
+ * (the production default) every claude task falls through to the unchanged PTY path;
+ * with it on, only chat-tab claude tasks (session_id + chat_id) route to the SDK.
+ */
+const ON = { CLAUDE_SDK_BACKEND: '1' } as NodeJS.ProcessEnv;
+const OFF = {} as NodeJS.ProcessEnv;
+
+describe('claudeSdkBackendEnabled', () => {
+  it('is false when unset or falsy', () => {
+    expect(claudeSdkBackendEnabled({} as NodeJS.ProcessEnv)).toBe(false);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: '' } as NodeJS.ProcessEnv)).toBe(false);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: '0' } as NodeJS.ProcessEnv)).toBe(false);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: 'false' } as NodeJS.ProcessEnv)).toBe(false);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: 'off' } as NodeJS.ProcessEnv)).toBe(false);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: 'no' } as NodeJS.ProcessEnv)).toBe(false);
+  });
+
+  it('is true for any other truthy value', () => {
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: '1' } as NodeJS.ProcessEnv)).toBe(true);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: 'true' } as NodeJS.ProcessEnv)).toBe(true);
+    expect(claudeSdkBackendEnabled({ CLAUDE_SDK_BACKEND: 'on' } as NodeJS.ProcessEnv)).toBe(true);
+  });
+});
+
+describe('shouldUseClaudeSdk', () => {
+  it('is always false while the env flag is off — production claude stays on PTY', () => {
+    expect(shouldUseClaudeSdk({ agent: 'claude', session_id: 's1', chat_id: 'c1' }, OFF)).toBe(false);
+  });
+
+  it('routes a chat-tab claude task to the SDK when the flag is on', () => {
+    expect(shouldUseClaudeSdk({ agent: 'claude', session_id: 's1', chat_id: 'c1' }, ON)).toBe(true);
+  });
+
+  it('only applies to the claude agent', () => {
+    expect(shouldUseClaudeSdk({ agent: 'qwen', session_id: 's1', chat_id: 'c1' }, ON)).toBe(false);
+    expect(shouldUseClaudeSdk({ agent: 'opencode', session_id: 's1', chat_id: 'c1' }, ON)).toBe(false);
+    expect(shouldUseClaudeSdk({ agent: null, session_id: 's1', chat_id: 'c1' }, ON)).toBe(false);
+  });
+
+  it('requires both session_id and chat_id (session-less creators stay one-shot)', () => {
+    expect(shouldUseClaudeSdk({ agent: 'claude', session_id: null, chat_id: null }, ON)).toBe(false);
+    expect(shouldUseClaudeSdk({ agent: 'claude', session_id: 's1', chat_id: null }, ON)).toBe(false);
+    expect(shouldUseClaudeSdk({ agent: 'claude', session_id: null, chat_id: 'c1' }, ON)).toBe(false);
+  });
+});

apps/coder/src/services/backends/__tests__/claude-session-store.test.ts

@@ -0,0 +1,135 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import postgres from 'postgres';
+import { PostgresSessionStore } from '../claude-session-store.js';
+import type { SessionStoreEntry } from '@anthropic-ai/claude-agent-sdk';
+
+/**
+ * claude-sdk-sessionstore #9 (Part 1) — PostgresSessionStore tests.
+ *
+ * DB-opt-in (DATABASE_URL), mirrors checkpoints.test.ts: skips cleanly when the
+ * var is unset; otherwise applies the server + coder schemas and exercises the
+ * real append/load/listSessions/delete/listSubkeys round trips against postgres.
+ * Rows are namespaced under a unique project_key so concurrent suites / leftover
+ * data can't collide, and afterAll deletes everything written.
+ */
+describe.runIf(!!process.env.DATABASE_URL)('PostgresSessionStore (DB)', () => {
+  let sql: ReturnType<typeof postgres>;
+  let store: PostgresSessionStore;
+  const projectKey = `claude-store-test-${Date.now()}`;
+
+  const entry = (type: string, extra: Record<string, unknown> = {}): SessionStoreEntry => ({
+    type,
+    ...extra,
+  });
+
+  beforeAll(async () => {
+    sql = postgres(process.env.DATABASE_URL!, { max: 3 });
+    const serverSchema = resolve(__dirname, '../../../../../server/src/schema.sql');
+    const coderSchema = resolve(__dirname, '../../../schema.sql');
+    await sql.unsafe(readFileSync(serverSchema, 'utf8'));
+    await sql.unsafe(readFileSync(coderSchema, 'utf8'));
+    store = new PostgresSessionStore(sql);
+  });
+
+  afterAll(async () => {
+    if (sql) {
+      await sql`DELETE FROM claude_session_entries WHERE project_key = ${projectKey}`.catch(() => {});
+      await sql.end({ timeout: 5 });
+    }
+  });
+
+  it('append → load round-trips and preserves order across two appends', async () => {
+    const key = { projectKey, sessionId: 'sess-order' };
+    await store.append(key, [entry('user', { uuid: 'u1' }), entry('assistant', { uuid: 'a1' })]);
+    await store.append(key, [entry('result', { uuid: 'r1' })]);
+
+    const loaded = await store.load(key);
+    expect(loaded).not.toBeNull();
+    expect(loaded!.map((e) => e.uuid)).toEqual(['u1', 'a1', 'r1']);
+    expect(loaded!.map((e) => e.type)).toEqual(['user', 'assistant', 'result']);
+  });
+
+  it('append with an empty batch is a no-op (load still null for an otherwise-unseen key)', async () => {
+    const key = { projectKey, sessionId: 'sess-empty' };
+    await store.append(key, []);
+    expect(await store.load(key)).toBeNull();
+  });
+
+  it('load of a key that was never written returns null', async () => {
+    expect(await store.load({ projectKey, sessionId: 'never-seen' })).toBeNull();
+  });
+
+  it('isolates the main transcript from a subpath (load each independently)', async () => {
+    const sessionId = 'sess-subpath';
+    const mainKey = { projectKey, sessionId };
+    const subKey = { projectKey, sessionId, subpath: 'subagents/x' };
+
+    await store.append(mainKey, [entry('user', { uuid: 'main-1' })]);
+    await store.append(subKey, [entry('assistant', { uuid: 'sub-1' })]);
+
+    const main = await store.load(mainKey);
+    const sub = await store.load(subKey);
+    expect(main!.map((e) => e.uuid)).toEqual(['main-1']);
+    expect(sub!.map((e) => e.uuid)).toEqual(['sub-1']);
+  });
+
+  it('listSessions returns the session with a numeric mtime (main transcripts only)', async () => {
+    const sessionId = 'sess-list';
+    await store.append({ projectKey, sessionId }, [entry('user', { uuid: 'l1' })]);
+    // A subagent-only session must NOT surface as a main-transcript session.
+    await store.append(
+      { projectKey, sessionId: 'sess-sub-only', subpath: 'subagents/y' },
+      [entry('user', { uuid: 's1' })],
+    );
+
+    const sessions = await store.listSessions(projectKey);
+    const ids = sessions.map((s) => s.sessionId);
+    expect(ids).toContain(sessionId);
+    expect(ids).not.toContain('sess-sub-only');
+
+    const row = sessions.find((s) => s.sessionId === sessionId)!;
+    expect(typeof row.mtime).toBe('number');
+    expect(Number.isFinite(row.mtime)).toBe(true);
+    expect(row.mtime).toBeGreaterThan(0);
+  });
+
+  it('delete with a subpath removes only that subpath', async () => {
+    const sessionId = 'sess-del-subpath';
+    const mainKey = { projectKey, sessionId };
+    const subKey = { projectKey, sessionId, subpath: 'subagents/z' };
+    await store.append(mainKey, [entry('user', { uuid: 'keep-1' })]);
+    await store.append(subKey, [entry('assistant', { uuid: 'drop-1' })]);
+
+    await store.delete(subKey);
+
+    expect(await store.load(subKey)).toBeNull();
+    expect((await store.load(mainKey))!.map((e) => e.uuid)).toEqual(['keep-1']);
+  });
+
+  it('delete without a subpath removes the whole session (all subpaths)', async () => {
+    const sessionId = 'sess-del-all';
+    const mainKey = { projectKey, sessionId };
+    const subKey = { projectKey, sessionId, subpath: 'subagents/w' };
+    await store.append(mainKey, [entry('user', { uuid: 'm' })]);
+    await store.append(subKey, [entry('assistant', { uuid: 's' })]);
+
+    await store.delete({ projectKey, sessionId });
+
+    expect(await store.load(mainKey)).toBeNull();
+    expect(await store.load(subKey)).toBeNull();
+    expect(await store.listSubkeys({ projectKey, sessionId })).toEqual([]);
+  });
+
+  it('listSubkeys returns the distinct non-main subpaths', async () => {
+    const sessionId = 'sess-subkeys';
+    await store.append({ projectKey, sessionId }, [entry('user', { uuid: 'main' })]);
+    await store.append({ projectKey, sessionId, subpath: 'subagents/a' }, [entry('user', { uuid: 'a1' })]);
+    await store.append({ projectKey, sessionId, subpath: 'subagents/a' }, [entry('user', { uuid: 'a2' })]);
+    await store.append({ projectKey, sessionId, subpath: 'subagents/b' }, [entry('user', { uuid: 'b1' })]);
+
+    const subkeys = await store.listSubkeys({ projectKey, sessionId });
+    expect(subkeys.sort()).toEqual(['subagents/a', 'subagents/b']);
+  });
+});

apps/coder/src/services/backends/__tests__/pushable-iterable.test.ts

@@ -0,0 +1,96 @@
+import { describe, it, expect } from 'vitest';
+import { createPushable } from '../pushable-iterable.js';
+
+/**
+ * The pushable async-iterable that feeds the Claude SDK's streaming-input query()
+ * one message per turn while staying open across turns. Tests cover the ordering
+ * contract (push/close/async-iterate) without any SDK shape.
+ */
+describe('createPushable — push/iterate ordering', () => {
+  it('yields buffered values in FIFO order then parks', async () => {
+    const p = createPushable<number>();
+    const it = p.iterable[Symbol.asyncIterator]();
+
+    p.push(1);
+    p.push(2);
+    expect(await it.next()).toEqual({ value: 1, done: false });
+    expect(await it.next()).toEqual({ value: 2, done: false });
+
+    // No more buffered → next() parks; resolve it by pushing.
+    const parked = it.next();
+    p.push(3);
+    expect(await parked).toEqual({ value: 3, done: false });
+  });
+
+  it('hands a value directly to a parked consumer (push after await)', async () => {
+    const p = createPushable<string>();
+    const it = p.iterable[Symbol.asyncIterator]();
+    const pending = it.next(); // parks immediately (empty buffer)
+    p.push('hello');
+    expect(await pending).toEqual({ value: 'hello', done: false });
+  });
+
+  it('close() resolves a parked consumer as done and reports done thereafter', async () => {
+    const p = createPushable<number>();
+    const it = p.iterable[Symbol.asyncIterator]();
+    const pending = it.next();
+    p.close();
+    expect(await pending).toEqual({ value: undefined, done: true });
+    expect(await it.next()).toEqual({ value: undefined, done: true });
+    expect(p.closed).toBe(true);
+  });
+
+  it('still drains values buffered BEFORE close', async () => {
+    const p = createPushable<number>();
+    const it = p.iterable[Symbol.asyncIterator]();
+    p.push(10);
+    p.push(20);
+    p.close();
+    expect(await it.next()).toEqual({ value: 10, done: false });
+    expect(await it.next()).toEqual({ value: 20, done: false });
+    expect(await it.next()).toEqual({ value: undefined, done: true });
+  });
+
+  it('drops values pushed after close', async () => {
+    const p = createPushable<number>();
+    const it = p.iterable[Symbol.asyncIterator]();
+    p.close();
+    p.push(99); // no-op
+    expect(await it.next()).toEqual({ value: undefined, done: true });
+  });
+
+  it('close() is idempotent', () => {
+    const p = createPushable<number>();
+    p.close();
+    expect(() => p.close()).not.toThrow();
+    expect(p.closed).toBe(true);
+  });
+
+  it('works with a for-await loop driven by interleaved pushes', async () => {
+    const p = createPushable<number>();
+    const seen: number[] = [];
+    const consumer = (async () => {
+      for await (const v of p.iterable) seen.push(v);
+    })();
+
+    p.push(1);
+    await Promise.resolve();
+    p.push(2);
+    await Promise.resolve();
+    p.close();
+    await consumer;
+    expect(seen).toEqual([1, 2]);
+  });
+
+  it('return() on the iterator closes the queue (for-await break)', async () => {
+    const p = createPushable<number>();
+    const it = p.iterable[Symbol.asyncIterator]();
+    p.push(1);
+    expect(await it.next()).toEqual({ value: 1, done: false });
+    // Simulate a `break` in for-await: the runtime calls return().
+    expect(await it.return!()).toEqual({ value: undefined, done: true });
+    expect(p.closed).toBe(true);
+    p.push(2); // dropped — queue is closed
+    expect(await it.next()).toEqual({ value: undefined, done: true });
+  });
+});

apps/coder/src/services/backends/claude-sdk-map.ts

@@ -0,0 +1,192 @@
+/**
+ * claude-sdk-sessionstore #9 (Part 2) — PURE Claude-SDK message → AgentEvent mapper.
+ *
+ * `ClaudeSdkBackend` drives one `query()` per (chat, agent) session and feeds each
+ * `SDKMessage` it yields through this function, forwarding the returned
+ * `AgentEvent[]` to the dispatcher's `onEvent` (which maps them to WS frames +
+ * persists). Kept PURE (one message + a caller-owned accumulator → events) so it's
+ * unit-testable without a live `claude` binary — the whole point of Part 2's
+ * typecheck-and-unit-test gate (the live pump needs a host smoke).
+ *
+ * SDK shapes (verified against @anthropic-ai/claude-agent-sdk@0.3.159 sdk.d.ts +
+ * @anthropic-ai/sdk beta messages d.ts):
+ *   - `SDKPartialAssistantMessage` (`type:'stream_event'`) carries a
+ *     `BetaRawMessageStreamEvent` — the LIVE delta stream (only emitted when
+ *     `options.includePartialMessages` is set, which the backend sets). We map:
+ *       · content_block_delta + text_delta      → { text }
+ *       · content_block_delta + thinking_delta   → { reasoning }
+ *       · content_block_start  + tool_use block  → { tool_call } (in_progress)
+ *       · content_block_delta + input_json_delta → buffered into the tool's args
+ *         (no event; the assembled input rides the terminal tool_update)
+ *   - `SDKAssistantMessage` (`type:'assistant'`) carries the FINAL `message.content`
+ *     blocks. Text/thinking there are post-hoc repeats of what the partials already
+ *     streamed, so we DROP them (dedup) and only emit a terminal `tool_update`
+ *     (status completed) per `tool_use` block, with its now-complete `input`.
+ *   - All other `SDKMessage` variants (system/init, status, result, hooks, task
+ *     notifications, …) carry no renderable turn content → return [].
+ *
+ * Tool assembly spans messages: a tool_use block opens in a partial
+ * `content_block_start`, its args stream as `input_json_delta` frames keyed by the
+ * block `index`, and the final assistant message restates the complete block. The
+ * caller owns a `ClaudeSdkMapState` (snapshot map + per-index tool tracking) that
+ * threads this across calls, mirroring the `Map<string, AcpToolSnapshot>` the other
+ * backends pass into `mapSessionUpdate`. The result frames carry the SAME
+ * `AcpToolSnapshot` shape, so `persistExternalAgentTurn` / `snapshotToWireToolCall`
+ * are reused unchanged.
+ */
+import type { SDKMessage } from '@anthropic-ai/claude-agent-sdk';
+import type { AgentEvent } from '../agent-backend.js';
+import type { AcpToolSnapshot } from '../acp-tool-snapshot.js';
+
+/**
+ * The underlying `@anthropic-ai/sdk` Beta message types (`BetaRawMessageStreamEvent`,
+ * `BetaContentBlock`) are a TRANSITIVE dep of `@anthropic-ai/claude-agent-sdk` — not
+ * a direct dependency of apps/coder — so a `@anthropic-ai/sdk/...` import does NOT
+ * resolve here under pnpm's strict node_modules. We instead DERIVE both shapes from
+ * the SDK's own exported message types, which is also more correct (it tracks the
+ * exact `event` / `content` shapes the SDK yields, not a hand-picked import path).
+ */
+type StreamEvent = Extract<SDKMessage, { type: 'stream_event' }>['event'];
+type AssistantContent = Extract<SDKMessage, { type: 'assistant' }>['message']['content'];
+type ContentBlock = AssistantContent extends readonly (infer B)[] ? B : never;
+
+/**
+ * Caller-owned accumulator threaded across `mapSdkMessage` calls within ONE turn.
+ * The backend creates a fresh one per turn and clears it at turn end.
+ */
+export interface ClaudeSdkMapState {
+  /** Stable tool-call snapshots by tool_use id, merged across start/delta/stop. */
+  snapshots: Map<string, AcpToolSnapshot>;
+  /**
+   * Partial-stream block index → in-flight tool assembly. Anthropic's stream keys
+   * blocks by a numeric `index`; tool_use args arrive as `input_json_delta`s under
+   * that index with no id, so we map index→id to route them and buffer the raw
+   * JSON fragments until the block closes (or the final assistant message lands).
+   */
+  toolByIndex: Map<number, { id: string; name: string; jsonBuf: string }>;
+}
+
+/** Construct a fresh per-turn accumulator. */
+export function createClaudeSdkMapState(): ClaudeSdkMapState {
+  return { snapshots: new Map(), toolByIndex: new Map() };
+}
+
+/**
+ * Map one `SDKMessage` → zero or more `AgentEvent`s, mutating `state` for
+ * cross-message tool assembly + dedup. Pure w.r.t. its inputs otherwise.
+ */
+export function mapSdkMessage(msg: SDKMessage, state: ClaudeSdkMapState): AgentEvent[] {
+  switch (msg.type) {
+    case 'stream_event':
+      return mapStreamEvent(msg.event, state);
+    case 'assistant':
+      return mapFinalAssistant(msg.message.content, state);
+    default:
+      // system/init, status, result, hooks, task_*, etc. — no turn content here.
+      // (The backend reads session_id off the init message and usage/cost off the
+      // result message directly; neither produces a renderable AgentEvent.)
+      return [];
+  }
+}
+
+/** Live partial-stream delta → AgentEvent(s). */
+function mapStreamEvent(event: StreamEvent, state: ClaudeSdkMapState): AgentEvent[] {
+  switch (event.type) {
+    case 'content_block_start': {
+      const block = event.content_block;
+      if (block.type === 'tool_use') {
+        const snap: AcpToolSnapshot = {
+          toolCallId: block.id,
+          title: block.name,
+          kind: null,
+          status: 'in_progress',
+          rawInput: block.input ?? undefined,
+          rawOutput: undefined,
+        };
+        state.snapshots.set(block.id, snap);
+        state.toolByIndex.set(event.index, { id: block.id, name: block.name, jsonBuf: '' });
+        return [{ type: 'tool_call', toolCall: snap }];
+      }
+      return [];
+    }
+    case 'content_block_delta': {
+      const delta = event.delta;
+      if (delta.type === 'text_delta') {
+        return delta.text ? [{ type: 'text', text: delta.text }] : [];
+      }
+      if (delta.type === 'thinking_delta') {
+        return delta.thinking ? [{ type: 'reasoning', text: delta.thinking }] : [];
+      }
+      if (delta.type === 'input_json_delta') {
+        // Buffer the tool's streamed args under its block index; no event yet —
+        // the assembled input rides the terminal tool_update (or the final block).
+        const t = state.toolByIndex.get(event.index);
+        if (t) t.jsonBuf += delta.partial_json ?? '';
+        return [];
+      }
+      // signature_delta / citations_delta / compaction_delta — nothing to render.
+      return [];
+    }
+    case 'content_block_stop': {
+      // Close out a streamed tool block: parse its buffered JSON args and emit a
+      // tool_update carrying the assembled input. The final assistant message will
+      // restate the same block, but its snapshot is dedup-merged (same id) so this
+      // is harmless — we emit here so a tool's input renders even if the assistant
+      // message is delayed/dropped.
+      const t = state.toolByIndex.get(event.index);
+      if (!t) return [];
+      state.toolByIndex.delete(event.index);
+      const prev = state.snapshots.get(t.id);
+      const snap: AcpToolSnapshot = {
+        toolCallId: t.id,
+        title: prev?.title ?? t.name,
+        kind: null,
+        status: 'in_progress',
+        rawInput: parseJsonOr(t.jsonBuf, prev?.rawInput),
+        rawOutput: undefined,
+      };
+      state.snapshots.set(t.id, snap);
+      return [{ type: 'tool_update', toolCall: snap }];
+    }
+    default:
+      // message_start / message_delta / message_stop — turn framing, no content.
+      return [];
+  }
+}
+
+/**
+ * Final assistant message content blocks. Text/thinking are post-hoc repeats of
+ * the partial stream → dropped (dedup). Only tool_use blocks emit a terminal
+ * tool_update carrying the complete `input`.
+ */
+function mapFinalAssistant(content: ContentBlock[], state: ClaudeSdkMapState): AgentEvent[] {
+  const out: AgentEvent[] = [];
+  for (const block of content) {
+    if (block.type === 'tool_use') {
+      const prev = state.snapshots.get(block.id);
+      const snap: AcpToolSnapshot = {
+        toolCallId: block.id,
+        title: prev?.title ?? block.name,
+        kind: null,
+        status: 'completed',
+        rawInput: block.input ?? prev?.rawInput,
+        rawOutput: undefined,
+      };
+      state.snapshots.set(block.id, snap);
+      out.push({ type: 'tool_update', toolCall: snap });
+    }
+    // text / thinking / redacted_thinking blocks: already streamed via partials.
+  }
+  return out;
+}
+
+/** Parse a buffered JSON string; fall back to a prior value on empty/invalid. */
+function parseJsonOr(buf: string, fallback: unknown): unknown {
+  const s = buf.trim();
+  if (!s) return fallback;
+  try {
+    return JSON.parse(s);
+  } catch {
+    return fallback;
+  }
+}

apps/coder/src/services/backends/claude-sdk-routing.ts

@@ -0,0 +1,38 @@
+/**
+ * claude-sdk-sessionstore #9 (Part 2) — claude-SDK-vs-PTY routing predicate.
+ *
+ * Sibling to `shouldUseWarmBackend` (warm-acp-routing.ts). The warm Claude-SDK
+ * backend keys its persistent `query()` on (chat_id, agent) — exactly like the
+ * warm-ACP / opencode-server backends — so a task only routes to it when it carries
+ * BOTH a `session_id` and a `chat_id` (a real chat tab).
+ *
+ * CRUCIALLY this is ALSO gated behind the `CLAUDE_SDK_BACKEND` env flag (default
+ * OFF). While off — the production default — claude always falls through to the
+ * existing one-shot PTY `runExternalAgent` path, UNCHANGED. The live SDK streaming
+ * pump + cross-turn resume need a host smoke against the real `claude` binary, so
+ * we keep the working PTY path as the default until that lands. Flip the env var
+ * on a host (any truthy value) to opt a deployment into the SDK backend.
+ *
+ * Pure (env read injected) so it's unit-testable; the dispatcher consumes it.
+ */
+
+/** True iff the `CLAUDE_SDK_BACKEND` env flag is set to a truthy value. */
+export function claudeSdkBackendEnabled(env: NodeJS.ProcessEnv = process.env): boolean {
+  const v = env.CLAUDE_SDK_BACKEND;
+  if (v == null) return false;
+  const s = v.trim().toLowerCase();
+  return s !== '' && s !== '0' && s !== 'false' && s !== 'off' && s !== 'no';
+}
+
+export function shouldUseClaudeSdk(
+  task: {
+    agent: string | null;
+    session_id: string | null;
+    chat_id: string | null;
+  },
+  env: NodeJS.ProcessEnv = process.env,
+): boolean {
+  if (!claudeSdkBackendEnabled(env)) return false;
+  if (task.agent !== 'claude') return false;
+  return task.session_id != null && task.chat_id != null;
+}

apps/coder/src/services/backends/claude-sdk.ts

@@ -0,0 +1,364 @@
+/**
+ * claude-sdk-sessionstore #9 (Part 2) — ClaudeSdkBackend.
+ *
+ * A warm, resumable backend for the `claude` agent built on the Claude Agent SDK
+ * (`@anthropic-ai/claude-agent-sdk`), implementing the Phase-0 `AgentBackend`
+ * contract (same shape as `WarmAcpBackend` / `OpenCodeServerBackend`). One
+ * persistent `query()` per (chat, agent) session, driven in STREAMING-INPUT mode:
+ * the `prompt` is a pushable `AsyncIterable<SDKUserMessage>` that stays open across
+ * turns, so the SDK subprocess + conversation stay warm between `prompt()` calls
+ * until `closeSession`/`dispose`.
+ *
+ * ⚠ LIVE PUMP IS HOST-ONLY. The actual streaming turn needs the real `claude`
+ * binary + ANTHROPIC auth on a host — it CANNOT run in the dev container. This file
+ * is written against the REAL SDK types so it TYPECHECKS, and the PURE pieces (the
+ * `mapSdkMessage` mapper + the `createPushable` queue) are unit-tested. Routing to
+ * this backend is gated behind `CLAUDE_SDK_BACKEND` (default OFF) so production
+ * claude stays on the working PTY path until a host smoke validates the pump +
+ * cross-turn resume.
+ *
+ * Lifecycle (mirrors warm-acp.ts / opencode-server.ts):
+ *   - `ensureSession`: resolve the resume id from `agent_sessions(chat_id,'claude')`
+ *     and (re)build the single `query()` if not already live. The SDK's own
+ *     `sessionStore` (Part 1 PostgresSessionStore) materializes the transcript on
+ *     resume; `options.resume` carries the provider session id.
+ *   - `prompt`: push ONE user message onto the open queue, iterate the generator,
+ *     map each `SDKMessage` → `AgentEvent`s via `mapSdkMessage`, forward to
+ *     `ctx.onEvent`, and resolve when the turn's `result` message lands. Capture the
+ *     `session_id` from the `init` message and persist it to `agent_sessions`;
+ *     accumulate `result.usage` / `total_cost_usd` onto the row (mirrors opencode U.6).
+ *   - `closeSession` / `dispose`: close the queue + dispose the query generator.
+ *   - A thrown error or `result.subtype==='error*'` marks `agent_sessions.status='crashed'`.
+ *
+ * Turn serialization: like warm-acp, exactly one turn is in flight at a time on a
+ * given backend (the dispatcher's per-session `inflight` map enforces this upstream;
+ * `isBusy()` reports it so the pool never evicts mid-turn).
+ */
+import { query, type Query, type SDKMessage, type SDKUserMessage, type Options } from '@anthropic-ai/claude-agent-sdk';
+import type { FastifyBaseLogger } from 'fastify';
+import type { Sql } from '../../db.js';
+import { PostgresSessionStore } from './claude-session-store.js';
+import { createPushable, type Pushable } from './pushable-iterable.js';
+import { mapSdkMessage, createClaudeSdkMapState, type ClaudeSdkMapState } from './claude-sdk-map.js';
+import type {
+  AgentBackend,
+  AgentSessionHandle,
+  EnsureSessionOpts,
+  PromptCtx,
+  TurnResult,
+} from '../agent-backend.js';
+
+export interface ClaudeSdkBackendDeps {
+  sql: Sql;
+  log: FastifyBaseLogger;
+  /** The (chat, agent) this backend serves — its pool identity + DB key. */
+  chatId: string;
+  /** Always 'claude' today; kept explicit so the pool key + DB writes stay honest. */
+  agent: string;
+  /** Resolved `claude` binary path (available_agents.install_path); null → SDK default. */
+  installPath: string | null;
+}
+
+export class ClaudeSdkBackend implements AgentBackend {
+  readonly backend = 'claude_sdk' as const;
+
+  private readonly sql: Sql;
+  private readonly log: FastifyBaseLogger;
+  private readonly chatId: string;
+  private readonly agent: string;
+  private readonly installPath: string | null;
+  private readonly sessionStore: PostgresSessionStore;
+
+  /** The single persistent query() generator; null until the first turn builds it. */
+  private query: Query | null = null;
+  /** The open input queue feeding the generator one SDKUserMessage per turn. */
+  private input: Pushable<SDKUserMessage> | null = null;
+  /** The provider's own session id (resume token), captured from the init message. */
+  private agentSessionId: string | null = null;
+  /** Resolved model the live query() was built with; a change forces a rebuild. */
+  private builtModel: string | null = null;
+  /** True between prompt() start and settle. */
+  private busy = false;
+  private up = false;
+
+  constructor(deps: ClaudeSdkBackendDeps) {
+    this.sql = deps.sql;
+    this.log = deps.log;
+    this.chatId = deps.chatId;
+    this.agent = deps.agent;
+    this.installPath = deps.installPath;
+    this.sessionStore = new PostgresSessionStore(deps.sql);
+  }
+
+  /** §2: liveness for the health endpoint + dispatcher fallback decision. */
+  health(): 'up' | 'down' {
+    return this.up ? 'up' : 'down';
+  }
+
+  /** Phase 3: busy iff a turn is in flight (pool never evicts a busy backend). */
+  isBusy(): boolean {
+    return this.busy;
+  }
+
+  // ─── ensureSession: resolve resume id + (re)build the warm query ──────────────
+
+  async ensureSession(sessionId: string, opts: EnsureSessionOpts): Promise<AgentSessionHandle> {
+    // Resolve the resume token from the (chat_id, agent) row. A crashed row is not
+    // resumed (the SDK would fail to load a dead session); we create fresh.
+    const [row] = await this.sql<{ agent_session_id: string | null; status: string }[]>`
+      SELECT agent_session_id, status FROM agent_sessions
+      WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
+    `;
+    const resumeId = row && row.status !== 'crashed' ? row.agent_session_id : null;
+
+    // (Re)build the warm query if there is none, or the model changed (the SDK can
+    // change model mid-session via setModel, but a fresh build is simplest + matches
+    // opencode's config-drift → fresh-session rule). The query stays alive across
+    // turns; only closeSession/dispose tears it down.
+    if (!this.query || this.builtModel !== opts.model) {
+      await this.teardownQuery();
+      this.buildQuery(opts.worktreePath, opts.model, resumeId);
+    }
+
+    // Seed the in-memory resume id from the DB so a handle built before the first
+    // turn's init message still carries the last-known token. The init message
+    // overwrites it with the authoritative current id during the turn.
+    if (this.agentSessionId == null) this.agentSessionId = resumeId;
+
+    // Upsert the agent_sessions row (backend='claude_sdk'). agent_session_id may be
+    // null until the first turn captures it from the init message; prompt() updates it.
+    await this.sql`
+      INSERT INTO agent_sessions
+        (chat_id, session_id, worktree_id, agent, backend, agent_session_id, server_port, status, last_active_at)
+      VALUES
+        (${opts.chatId}, ${sessionId}, ${opts.worktreeId}, ${opts.agent}, 'claude_sdk', ${this.agentSessionId}, NULL, 'active', clock_timestamp())
+      ON CONFLICT (chat_id, agent) DO UPDATE SET
+        session_id = EXCLUDED.session_id,
+        worktree_id = EXCLUDED.worktree_id,
+        backend = 'claude_sdk',
+        agent_session_id = COALESCE(EXCLUDED.agent_session_id, agent_sessions.agent_session_id),
+        server_port = NULL,
+        status = 'active',
+        last_active_at = clock_timestamp()
+    `.catch((err) => {
+      this.log.warn({ err: errMsg(err), chatId: opts.chatId, agent: opts.agent }, 'claude-sdk: agent_sessions upsert failed (non-fatal)');
+    });
+
+    return {
+      sessionId,
+      agent: opts.agent,
+      backend: 'claude_sdk',
+      chatId: opts.chatId,
+      worktreeId: opts.worktreeId,
+      agentSessionId: this.agentSessionId,
+      serverPort: null,
+    };
+  }
+
+  /** Build the persistent query() in streaming-input mode. Lazy — no subprocess
+   *  work happens until the generator is first iterated in prompt(). */
+  private buildQuery(worktreePath: string, model: string, resumeId: string | null): void {
+    const input = createPushable<SDKUserMessage>();
+    const options: Options = {
+      sessionStore: this.sessionStore,
+      cwd: worktreePath,
+      // Stream partial assistant messages so text/thinking/tool deltas arrive live
+      // (the mapper reads them; without this only terminal messages land).
+      includePartialMessages: true,
+      ...(model ? { model } : {}),
+      ...(resumeId ? { resume: resumeId } : {}),
+      ...(this.installPath ? { pathToClaudeCodeExecutable: this.installPath } : {}),
+      // ANTHROPIC auth/env must reach the child; inherit the process env (host concern).
+      env: process.env as Record<string, string>,
+    };
+    this.input = input;
+    this.query = query({ prompt: input.iterable, options });
+    this.builtModel = model;
+    this.up = true;
+    this.log.info({ chatId: this.chatId, agent: this.agent, model, resume: resumeId ?? null }, 'claude-sdk: warm query built');
+  }
+
+  // ─── prompt: push one user message + drain the generator until result ─────────
+
+  async prompt(handle: AgentSessionHandle, input: string, ctx: PromptCtx): Promise<TurnResult> {
+    if (!this.query || !this.input) {
+      // ensureSession should have built it; rebuild defensively (e.g. evicted/raced).
+      this.buildQuery(ctx.worktreePath, ctx.model, handle.agentSessionId);
+    }
+    const gen = this.query!;
+    const queue = this.input!;
+
+    if (ctx.signal.aborted) return { ok: false, error: 'aborted' };
+
+    this.busy = true;
+    const state: ClaudeSdkMapState = createClaudeSdkMapState();
+    // Per-turn abort: interrupt the in-flight query on the SAME generator (never
+    // tear down the warm query — that's the pool's lifetime). The generator then
+    // emits its terminal result and the drain loop exits.
+    let aborted = false;
+    const onAbort = () => {
+      if (aborted) return;
+      aborted = true;
+      void gen.interrupt().catch(() => {});
+    };
+    ctx.signal.addEventListener('abort', onAbort, { once: true });
+
+    // Push the turn's user message onto the open queue. session_id is optional on
+    // the wire; the SDK manages it via resume + the init message.
+    const userMsg: SDKUserMessage = {
+      type: 'user',
+      message: { role: 'user', content: input },
+      parent_tool_use_id: null,
+      ...(handle.agentSessionId ? { session_id: handle.agentSessionId } : {}),
+    };
+    queue.push(userMsg);
+
+    try {
+      for await (const msg of gen) {
+        // Capture the provider session id from the init message (authoritative).
+        if (msg.type === 'system' && msg.subtype === 'init' && msg.session_id) {
+          if (this.agentSessionId !== msg.session_id) {
+            this.agentSessionId = msg.session_id;
+            await this.persistAgentSessionId(msg.session_id);
+          }
+        }
+        // The result message ends THIS turn (it does not close the generator —
+        // streaming-input keeps it alive for the next pushed message).
+        if (msg.type === 'result') {
+          await this.accumulateUsage(msg);
+          const ok = msg.subtype === 'success' && !aborted;
+          if (!ok) {
+            // error_during_execution / error_max_turns / aborted → crashed row.
+            await this.markCrashed();
+          } else {
+            await this.markIdle();
+          }
+          if (aborted) return { ok: false, error: 'aborted' };
+          return ok
+            ? { ok: true }
+            : { ok: false, error: resultErrorMessage(msg) };
+        }
+        // Map renderable content → AgentEvents for the dispatcher's onEvent.
+        for (const ev of mapSdkMessage(msg, state)) {
+          ctx.onEvent(ev);
+        }
+      }
+      // Generator ended without a result message (e.g. it was disposed) — treat as
+      // a non-fatal incomplete turn so the dispatcher still finalizes the row.
+      if (aborted) return { ok: false, error: 'aborted' };
+      return { ok: false, error: 'claude-sdk: query ended before result' };
+    } catch (err) {
+      if (aborted) return { ok: false, error: 'aborted' };
+      await this.markCrashed();
+      return { ok: false, error: errMsg(err) };
+    } finally {
+      ctx.signal.removeEventListener('abort', onAbort);
+      this.busy = false;
+    }
+  }
+
+  // ─── persistence helpers ──────────────────────────────────────────────────────
+
+  private async persistAgentSessionId(id: string): Promise<void> {
+    await this.sql`
+      UPDATE agent_sessions
+      SET agent_session_id = ${id}, last_active_at = clock_timestamp()
+      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
+    `.catch((err) => {
+      this.log.warn({ err: errMsg(err), chatId: this.chatId }, 'claude-sdk: failed to persist agent_session_id (non-fatal)');
+    });
+  }
+
+  /**
+   * Accumulate the turn's usage/cost onto the (chat_id, agent) row — mirrors the
+   * opencode U.6 running-total pattern. The SDK reports usage once per turn on the
+   * result message (not per step), so this fires once per prompt(). Cache read/write
+   * input tokens fold into `input_tokens`; usage telemetry never fails a turn.
+   */
+  private async accumulateUsage(result: Extract<SDKMessage, { type: 'result' }>): Promise<void> {
+    const u = result.usage;
+    const input = num(u?.input_tokens) + num(u?.cache_read_input_tokens) + num(u?.cache_creation_input_tokens);
+    const output = num(u?.output_tokens);
+    const cost = numF(result.total_cost_usd);
+    if (input === 0 && output === 0 && cost === 0) return;
+    await this.sql`
+      UPDATE agent_sessions SET
+        input_tokens = input_tokens + ${input},
+        output_tokens = output_tokens + ${output},
+        cost = cost + ${cost}
+      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
+    `.catch((err) => {
+      this.log.warn({ err: errMsg(err), chatId: this.chatId }, 'claude-sdk: failed to persist usage (non-fatal)');
+    });
+  }
+
+  private async markIdle(): Promise<void> {
+    await this.sql`
+      UPDATE agent_sessions SET status = 'idle', last_active_at = clock_timestamp()
+      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
+    `.catch(() => {});
+  }
+
+  private async markCrashed(): Promise<void> {
+    await this.sql`
+      UPDATE agent_sessions SET status = 'crashed'
+      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
+    `.catch(() => {});
+  }
+
+  // ─── teardown ────────────────────────────────────────────────────────────────
+
+  async closeSession(handle: AgentSessionHandle): Promise<void> {
+    await this.teardownQuery();
+    await this.sql`
+      UPDATE agent_sessions SET status = 'closed'
+      WHERE chat_id = ${handle.chatId} AND agent = ${handle.agent}
+    `.catch(() => {});
+  }
+
+  async dispose(): Promise<void> {
+    await this.teardownQuery();
+  }
+
+  /** Close the input queue + dispose the generator. Idempotent. */
+  private async teardownQuery(): Promise<void> {
+    this.up = false;
+    this.busy = false;
+    const q = this.query;
+    const queue = this.input;
+    this.query = null;
+    this.input = null;
+    this.builtModel = null;
+    queue?.close();
+    if (q) {
+      // return() ends the AsyncGenerator and lets the SDK clean up its subprocess.
+      await q.return(undefined).catch(() => {});
+    }
+  }
+}
+
+// ─── helpers ──────────────────────────────────────────────────────────────────
+
+/** Coerce to a non-negative finite integer (tokens). */
+function num(v: unknown): number {
+  const x = typeof v === 'number' ? v : Number(v);
+  return Number.isFinite(x) && x > 0 ? Math.round(x) : 0;
+}
+
+/** Coerce to a non-negative finite float (cost USD). */
+function numF(v: unknown): number {
+  const x = typeof v === 'number' ? v : Number(v);
+  return Number.isFinite(x) && x > 0 ? x : 0;
+}
+
+/** Build a human-readable error from an SDK error-result message. */
+function resultErrorMessage(result: Extract<SDKMessage, { type: 'result' }>): string {
+  if (result.subtype === 'success') return 'ok';
+  const errs = (result as { errors?: string[] }).errors;
+  if (Array.isArray(errs) && errs.length > 0) return `${result.subtype}: ${errs.join('; ')}`;
+  return result.subtype;
+}
+
+function errMsg(e: unknown): string {
+  return e instanceof Error ? e.message : String(e);
+}

apps/coder/src/services/backends/claude-session-store.ts

@@ -0,0 +1,117 @@
+import type { SessionStore, SessionKey, SessionStoreEntry } from '@anthropic-ai/claude-agent-sdk';
+import type { Sql } from '../../db.js';
+
+/**
+ * claude-sdk-sessionstore #9 (Part 1) — clean-room PostgresSessionStore.
+ *
+ * A Postgres-backed implementation of the Claude Agent SDK's `SessionStore`
+ * adapter type. The SDK mirrors each transcript line (a JSON-safe POJO with a
+ * `type` discriminant) to this store via `append`; on resume it calls `load`
+ * to materialize the full transcript back. We treat entries as opaque blobs and
+ * preserve append order via a BIGSERIAL `id` — `load` replays `ORDER BY id`.
+ *
+ * Storage shape: one row per entry in `claude_session_entries`, keyed by the
+ * SDK's `SessionKey` (project_key, session_id, subpath). The SDK uses an
+ * *undefined* subpath for the main transcript and disallows the empty string;
+ * we collapse `undefined → ''` so the main transcript and subagent files share
+ * one table, distinguished by the `subpath` column (`'' = main`).
+ *
+ * Clean-room: written against the SDK's published `SessionStore` type contract
+ * and BooCode's existing SQL conventions (porsager tagged templates, `sql.json`
+ * for JSONB). No SDK example/reference code was consulted.
+ */
+export class PostgresSessionStore implements SessionStore {
+  constructor(private readonly sql: Sql) {}
+
+  /**
+   * Mirror a batch of transcript entries. No-op on an empty batch; otherwise a
+   * single multi-row INSERT writes them in array order. Because `id` is a
+   * monotonically-increasing BIGSERIAL, the insert order is the replay order
+   * `load` reconstructs — entries within one call land in the order given.
+   */
+  async append(key: SessionKey, entries: SessionStoreEntry[]): Promise<void> {
+    if (entries.length === 0) return;
+    const subpath = key.subpath ?? '';
+    const rows = entries.map((entry) => ({
+      project_key: key.projectKey,
+      session_id: key.sessionId,
+      subpath,
+      entry: this.sql.json(entry as never),
+    }));
+    await this.sql`
+      INSERT INTO claude_session_entries ${this.sql(rows, 'project_key', 'session_id', 'subpath', 'entry')}
+    `;
+  }
+
+  /**
+   * Load a full transcript for resume. Returns the entries in append order, or
+   * `null` for a (project_key, session_id, subpath) key that was never written.
+   */
+  async load(key: SessionKey): Promise<SessionStoreEntry[] | null> {
+    const subpath = key.subpath ?? '';
+    const rows = await this.sql<{ entry: SessionStoreEntry }[]>`
+      SELECT entry
+      FROM claude_session_entries
+      WHERE project_key = ${key.projectKey}
+        AND session_id = ${key.sessionId}
+        AND subpath = ${subpath}
+      ORDER BY id
+    `;
+    if (rows.length === 0) return null;
+    return rows.map((r) => r.entry);
+  }
+
+  /**
+   * List the main transcripts for a project. `mtime` is the storage write time
+   * (latest `created_at` for the session) in Unix epoch milliseconds; the SDK
+   * sorts the result by mtime descending.
+   */
+  async listSessions(projectKey: string): Promise<Array<{ sessionId: string; mtime: number }>> {
+    const rows = await this.sql<{ session_id: string; mtime: string }[]>`
+      SELECT session_id, extract(epoch FROM max(created_at)) * 1000 AS mtime
+      FROM claude_session_entries
+      WHERE project_key = ${projectKey}
+        AND subpath = ''
+      GROUP BY session_id
+    `;
+    return rows.map((r) => ({ sessionId: r.session_id, mtime: Number(r.mtime) }));
+  }
+
+  /**
+   * Delete a session. With a `subpath` set, only that subpath's rows are
+   * removed; with `subpath` omitted, every row for the session is removed
+   * (all subpaths, including the main transcript).
+   */
+  async delete(key: SessionKey): Promise<void> {
+    if (key.subpath !== undefined) {
+      await this.sql`
+        DELETE FROM claude_session_entries
+        WHERE project_key = ${key.projectKey}
+          AND session_id = ${key.sessionId}
+          AND subpath = ${key.subpath}
+      `;
+      return;
+    }
+    await this.sql`
+      DELETE FROM claude_session_entries
+      WHERE project_key = ${key.projectKey}
+        AND session_id = ${key.sessionId}
+    `;
+  }
+
+  /**
+   * List the distinct non-main subpaths under a session (e.g. subagent files).
+   * Used during resume to discover and materialize subagent transcripts; the
+   * main transcript (`subpath = ''`) is excluded.
+   */
+  async listSubkeys(key: { projectKey: string; sessionId: string }): Promise<string[]> {
+    const rows = await this.sql<{ subpath: string }[]>`
+      SELECT DISTINCT subpath
+      FROM claude_session_entries
+      WHERE project_key = ${key.projectKey}
+        AND session_id = ${key.sessionId}
+        AND subpath <> ''
+    `;
+    return rows.map((r) => r.subpath);
+  }
+}

apps/coder/src/services/backends/pushable-iterable.ts

@@ -0,0 +1,96 @@
+/**
+ * claude-sdk-sessionstore #9 (Part 2) — a tiny PURE pushable async-iterable.
+ *
+ * The Claude Agent SDK's streaming-input mode wants `query({ prompt })` where
+ * `prompt` is an `AsyncIterable<SDKUserMessage>`. To keep ONE `query()` generator
+ * alive across many turns (the "warm" property), the backend feeds it ONE user
+ * message per `prompt()` turn through a queue that stays open between turns and is
+ * only closed at `closeSession`/`dispose`. This is that queue.
+ *
+ * Semantics (the bit worth unit-testing — push/close/iterate ordering):
+ *   - `push(v)` enqueues a value. If a consumer is parked in `await next()`, it's
+ *     handed the value immediately; otherwise the value buffers in FIFO order.
+ *   - The async iterator yields buffered/pushed values in push order, and PARKS
+ *     (never busy-loops) when the buffer is empty — so the SDK generator waits for
+ *     the next turn's message instead of seeing end-of-input.
+ *   - `close()` ends the iterable: any parked consumer resolves `{done:true}` and
+ *     all future `next()`s return done. Values pushed after close are dropped.
+ *   - It's single-consumer (one `query()` reads it); concurrent consumers are not a
+ *     supported shape and not needed here.
+ *
+ * No SDK import — generic over the pushed value `T` — so the pure push/close/iterate
+ * ordering is testable without the `SDKUserMessage` shape or a live binary.
+ */
+export interface Pushable<T> {
+  /** Enqueue a value (or hand it to a parked consumer). No-op after close. */
+  push(value: T): void;
+  /** End the iterable. Idempotent; a parked consumer resolves done. */
+  close(): void;
+  /** True once `close()` has been called. */
+  readonly closed: boolean;
+  /** The async-iterable the consumer (the SDK `query`) drives. */
+  readonly iterable: AsyncIterable<T>;
+}
+
+export function createPushable<T>(): Pushable<T> {
+  const buffer: T[] = [];
+  // A waiting consumer's resolver (null when none is parked). Single-consumer.
+  let pendingResolve: ((res: IteratorResult<T>) => void) | null = null;
+  let closed = false;
+
+  function push(value: T): void {
+    if (closed) return;
+    if (pendingResolve) {
+      const resolve = pendingResolve;
+      pendingResolve = null;
+      resolve({ value, done: false });
+      return;
+    }
+    buffer.push(value);
+  }
+
+  function close(): void {
+    if (closed) return;
+    closed = true;
+    if (pendingResolve) {
+      const resolve = pendingResolve;
+      pendingResolve = null;
+      resolve({ value: undefined, done: true });
+    }
+  }
+
+  const iterator: AsyncIterator<T> = {
+    next(): Promise<IteratorResult<T>> {
+      // Drain the buffer first (FIFO), regardless of close — buffered values
+      // pushed before close are still delivered.
+      if (buffer.length > 0) {
+        return Promise.resolve({ value: buffer.shift() as T, done: false });
+      }
+      if (closed) {
+        return Promise.resolve({ value: undefined, done: true });
+      }
+      // Park until the next push/close. Single-consumer: only one waiter at a time.
+      return new Promise<IteratorResult<T>>((resolve) => {
+        pendingResolve = resolve;
+      });
+    },
+    return(): Promise<IteratorResult<T>> {
+      // Consumer abandoned the loop (e.g. `break`) → close so a later push no-ops.
+      close();
+      return Promise.resolve({ value: undefined, done: true });
+    },
+  };
+
+  return {
+    push,
+    close,
+    get closed() {
+      return closed;
+    },
+    iterable: {
+      [Symbol.asyncIterator]() {
+        return iterator;
+      },
+    },
+  };
+}

apps/coder/src/services/dispatcher.ts

@@ -16,7 +16,9 @@ import { snapshotToWireToolCall, type AcpToolSnapshot } from './acp-tool-snapsho
 import { agentPool, OPENCODE_POOL_KEY } from './agent-pool.js';
 import { OpenCodeServerBackend } from './backends/opencode-server.js';
 import { WarmAcpBackend } from './backends/warm-acp.js';
+import { ClaudeSdkBackend } from './backends/claude-sdk.js';
 import { shouldUseWarmBackend } from './backends/warm-acp-routing.js';
+import { shouldUseClaudeSdk } from './backends/claude-sdk-routing.js';
 import type { AgentBackend, AgentEvent } from './agent-backend.js';
 
 interface InferenceRunner {
@@ -131,6 +133,12 @@ export function createDispatcher(deps: Deps): { start(): void; stop(): Promise<v
         // existing one-shot worktree-per-task ACP/PTY path untouched.
         if (task.agent === 'opencode') {
           await runOpenCodeServerTask(task, agentRow.install_path);
+        } else if (shouldUseClaudeSdk(task)) {
+          // claude-sdk-sessionstore #9 (Part 2): env-flagged (CLAUDE_SDK_BACKEND, default
+          // OFF) warm Claude-SDK backend for chat-tab claude tasks. When the flag is off
+          // (production default) this predicate returns false and claude falls through to
+          // the UNCHANGED one-shot PTY runExternalAgent path below.
+          await runClaudeSdkTask(task, agentRow.install_path);
         } else if (shouldUseWarmBackend(task)) {
           await runWarmAcpTask(task, agentRow.install_path);
         } else {
@@ -1129,6 +1137,247 @@ export function createDispatcher(deps: Deps): { start(): void; stop(): Promise<v
     }
   }
 
+  // ─── Path B (claude SDK): warm Claude-SDK backend (v2.6 #9 Part 2) ───────────
+
+  // Claude-SDK backends are per (chat, agent) — each owns ONE persistent query()
+  // generator driven in streaming-input mode. Pool key = chatId (secondary = agent),
+  // mirroring agent_sessions' (chat_id, agent) PK + the warm-ACP pooling.
+  function getClaudeSdkBackend(chatId: string, agent: string, installPath: string | null): ClaudeSdkBackend {
+    let backend = agentPool.get(chatId, agent);
+    if (!backend) {
+      backend = new ClaudeSdkBackend({ sql, log, chatId, agent, installPath });
+      agentPool.register(chatId, agent, backend);
+    }
+    return backend as ClaudeSdkBackend;
+  }
+
+  async function runClaudeSdkTask(
+    task: {
+      id: string;
+      project_id: string;
+      input: string;
+      agent: string | null;
+      model: string | null;
+      mode_id: string | null;
+      thinking_option_id: string | null;
+      session_id: string | null;
+      chat_id: string | null;
+    },
+    installPath: string | null,
+  ): Promise<void> {
+    const taskId = task.id;
+    const agent = task.agent!;
+    // shouldUseClaudeSdk guarantees both non-null before we get here.
+    const sessionId = task.session_id!;
+    const chatId = task.chat_id!;
+    log.info({ taskId, agent, chatId }, 'dispatcher: starting task (path B — claude SDK)');
+
+    const [project] = await sql<{ path: string | null }[]>`
+      SELECT path FROM projects WHERE id = ${task.project_id}
+    `;
+    const projectPath = project?.path;
+    if (!projectPath) {
+      await sql`
+        UPDATE tasks
+        SET state = 'failed', ended_at = clock_timestamp(), output_summary = 'Project has no path — cannot create worktree'
+        WHERE id = ${taskId}
+      `;
+      return;
+    }
+
+    const ac = new AbortController();
+
+    try {
+      await sql`
+        UPDATE tasks
+        SET state = 'running', started_at = clock_timestamp(), execution_path = 'acp'
+        WHERE id = ${taskId}
+      `;
+
+      // Persistent, session-keyed worktree (shared across turns + agents; NOT torn
+      // down per turn — Phase 3 reaps it). Same as the opencode/warm-ACP paths so a
+      // chat that switches agents shares one worktree.
+      const { worktreeId, worktreePath, baseCommit } = await ensureSessionWorktree(sql, projectPath, sessionId, {
+        signal: ac.signal,
+      });
+      log.info({ taskId, worktreePath }, 'dispatcher: session worktree ready (claude SDK)');
+
+      const [assistantMsg] = await sql<{ id: string }[]>`
+        INSERT INTO messages (session_id, chat_id, role, content, status, created_at)
+        VALUES (${sessionId}, ${chatId}, 'assistant', '', 'streaming', clock_timestamp())
+        RETURNING id
+      `;
+      const assistantId = assistantMsg!.id;
+
+      // write-edit-robustness #4: pre-turn checkpoint of the persistent session
+      // worktree (best-effort; never breaks dispatch).
+      await createCheckpoint(
+        sql,
+        { chatId, sessionId, worktreeId, worktreePath, messageId: assistantId },
+        { signal: ac.signal, log },
+      ).catch(() => null);
+
+      broker.publishFrame(sessionId, {
+        type: 'message_started',
+        message_id: assistantId,
+        chat_id: chatId,
+        role: 'assistant',
+      } as WsFrame);
+
+      const manifestCommands = getManifestCommands(agent);
+      if (manifestCommands.length > 0) {
+        setTaskCommands(taskId, manifestCommands);
+        broker.publishFrame(sessionId, {
+          type: 'agent_commands',
+          task_id: taskId,
+          session_id: sessionId,
+          commands: manifestCommands,
+        } as WsFrame);
+      }
+
+      // Accumulate the turn's stream for persistence + the final message content.
+      const textChunks: string[] = [];
+      const reasoningChunks: string[] = [];
+      const toolSnaps = new Map<string, AcpToolSnapshot>();
+
+      // Map transport-agnostic AgentEvents → the SAME WS frames the warm-ACP /
+      // opencode paths emit. This boundary attaches message_id/chat_id.
+      const onEvent = (e: AgentEvent): void => {
+        switch (e.type) {
+          case 'text':
+            textChunks.push(e.text);
+            broker.publishFrame(sessionId, {
+              type: 'delta',
+              message_id: assistantId,
+              chat_id: chatId,
+              content: e.text,
+            } as WsFrame);
+            break;
+          case 'reasoning':
+            reasoningChunks.push(e.text);
+            broker.publishFrame(sessionId, {
+              type: 'reasoning_delta',
+              message_id: assistantId,
+              chat_id: chatId,
+              content: e.text,
+            } as WsFrame);
+            break;
+          case 'tool_call':
+          case 'tool_update':
+            toolSnaps.set(e.toolCall.toolCallId, e.toolCall);
+            broker.publishFrame(sessionId, {
+              type: 'tool_call',
+              message_id: assistantId,
+              chat_id: chatId,
+              tool_call: snapshotToWireToolCall(e.toolCall),
+            } as WsFrame);
+            break;
+          case 'commands':
+            if (e.commands.length > 0) {
+              setTaskCommands(taskId, e.commands);
+              broker.publishFrame(sessionId, {
+                type: 'agent_commands',
+                task_id: taskId,
+                session_id: sessionId,
+                commands: e.commands,
+              } as WsFrame);
+            }
+            break;
+        }
+      };
+
+      const model = task.model ?? undefined;
+      const backend = getClaudeSdkBackend(chatId, agent, installPath);
+      const handle = await backend.ensureSession(sessionId, {
+        agent,
+        model: model ?? '',
+        chatId,
+        worktreePath,
+        worktreeId,
+        projectId: task.project_id,
+      });
+      const result = await backend.prompt(handle, task.input, {
+        worktreePath,
+        model: model ?? '',
+        signal: ac.signal,
+        onEvent,
+        taskId,
+        modeId: task.mode_id ?? undefined,
+      });
+      // Phase 3: keep the pooled (chat,agent) backend warm across the turn.
+      agentPool.touch(chatId, agent);
+
+      const assistantContent = textChunks.join('').slice(0, 50_000);
+      const reasoningText = reasoningChunks.join('').slice(0, 200_000);
+      const outputSummary = (result.ok ? textChunks.join('') : result.error ?? 'claude SDK turn failed').slice(0, 500);
+
+      await persistExternalAgentTurn(sql, assistantId, [...toolSnaps.values()], reasoningText);
+
+      await sql`
+        UPDATE messages
+        SET content = ${assistantContent}, status = 'complete', finished_at = clock_timestamp()
+        WHERE id = ${assistantId}
+      `;
+      broker.publishFrame(sessionId, {
+        type: 'message_complete',
+        message_id: assistantId,
+        chat_id: chatId,
+      } as WsFrame);
+
+      if (stopping) {
+        await sql`UPDATE tasks SET state = 'cancelled', ended_at = clock_timestamp() WHERE id = ${taskId}`;
+        return; // worktree persists (no cleanup); backend stays warm
+      }
+
+      // Diff the persistent worktree against its captured baseline and SUPERSEDE
+      // the session's prior pending row (latest-wins) — identical to opencode/ACP.
+      const diff = await diffWorktree(worktreePath, projectPath, {
+        signal: ac.signal,
+        baseRef: baseCommit ?? 'HEAD',
+      });
+      if (diff) {
+        await sql`
+          DELETE FROM pending_changes WHERE session_id = ${sessionId} AND status = 'pending'
+        `;
+        await sql`
+          INSERT INTO pending_changes (session_id, task_id, file_path, operation, diff, agent)
+          VALUES (${sessionId}, ${taskId}, ${projectPath}, 'edit', ${diff}, ${agent})
+        `;
+        log.info({ taskId, diffLength: diff.length }, 'dispatcher: diff superseded prior pending change (claude SDK)');
+      } else {
+        log.info({ taskId }, 'dispatcher: no changes detected in session worktree (claude SDK)');
+      }
+
+      // NO worktree cleanup — persistent (Phase 3 reaps it). Backend stays warm.
+
+      const [extCostRow] = await sql<{ total: number | null }[]>`
+        SELECT SUM(tokens_used)::int AS total
+        FROM messages
+        WHERE session_id = ${sessionId} AND tokens_used IS NOT NULL
+      `;
+      const extCostTokens = extCostRow?.total ?? null;
+
+      const finalState = result.ok ? 'completed' : 'failed';
+      await sql`
+        UPDATE tasks
+        SET state = ${finalState}, ended_at = clock_timestamp(), output_summary = ${outputSummary}, cost_tokens = ${extCostTokens}
+        WHERE id = ${taskId}
+      `;
+      log.info({ taskId, agent, finalState }, 'dispatcher: task finished (claude SDK)');
+      clearTaskCommands(taskId);
+    } catch (err) {
+      const errMsg = err instanceof Error ? err.message : String(err);
+      log.error({ taskId, agent, err: errMsg }, 'dispatcher: claude SDK error');
+      await sql`
+        UPDATE tasks
+        SET state = 'failed', ended_at = clock_timestamp(), output_summary = ${errMsg.slice(0, 500)}
+        WHERE id = ${taskId}
+      `.catch(() => {});
+      clearTaskCommands(taskId);
+      // No worktree cleanup (persistent); backend stays warm for the next turn.
+    }
+  }
+
   // ─── Helpers ────────────────────────────────────────────────────────────────
 
   async function waitForCompletion(assistantId: string): Promise<string> {

apps/coder/src/services/provider-registry.ts

@@ -38,6 +38,12 @@ export const PROVIDERS: ProviderDef[] = [
   },
   {
     name: 'claude',
+    // transport stays 'pty' — the DEFAULT dispatch path (one-shot `claude
+    // --output-format stream-json`). claude-sdk-sessionstore #9 (Part 2) adds a warm
+    // Claude-Agent-SDK backend (services/backends/claude-sdk.ts) routed ONLY when the
+    // `CLAUDE_SDK_BACKEND` env flag is truthy AND the task is a chat tab; with the flag
+    // off (production default) claude always uses this PTY path, so the transport label
+    // is left unchanged. Flip the env var on a host (after a live smoke) to opt in.
     label: 'Claude Code',
     transport: 'pty',
     modelSource: 'static',