fix(claude): preserve session across query restarts

Fixes the Claude query restart path that could drop conversation context after thinking effort changes or rewind-driven restarts.

Addresses #439.

Related to #156 and #200.

packages/server/src/server/agent/providers/claude-agent.interrupt-restart-regression.test.ts

@@ -338,6 +338,52 @@ test("reuses the existing query after interrupt before starting the next prompt"
   await session.close();
 });
 
+test("emits an assistant system notice when Claude changes session id mid-turn", async () => {
+  const logger = createTestLogger();
+  let queryRef: ScriptedQuery | null = null;
+
+  sdkMocks.query.mockImplementation(({ prompt }: { prompt: AsyncIterable<unknown> }) => {
+    queryRef = createScriptedQuery({
+      prompt,
+      sessionId: "claude-original-session",
+      async handlePrompt({ promptRecord, query }) {
+        if (promptRecord.text !== "trigger session switch") {
+          return;
+        }
+        query.emit({
+          type: "assistant",
+          message: { content: "Claude kept working." },
+          session_id: "claude-provider-switched-session",
+        });
+        query.emit(buildSuccessResult("claude-provider-switched-session"));
+      },
+    });
+    return queryRef;
+  });
+
+  const client = new ClaudeAgentClient({ logger });
+  const session = await client.createSession({
+    provider: "claude",
+    cwd: process.cwd(),
+  });
+
+  const events = await collectUntilTerminal(streamSession(session, "trigger session switch"));
+  const assistantMessages = events.flatMap((event) => {
+    if (event.type !== "timeline" || event.item.type !== "assistant_message") {
+      return [];
+    }
+    return [event.item.text];
+  });
+
+  expect(session.id).toBe("claude-provider-switched-session");
+  expect(assistantMessages).toContain("Claude kept working.");
+  expect(assistantMessages).toContain(
+    "Claude switched to a new session: claude-original-session -> claude-provider-switched-session",
+  );
+
+  await session.close();
+});
+
 test("recovers when the query pump sees a single interrupt abort before the next prompt", async () => {
   const logger = createTestLogger();
   const output = createAsyncQueue<Record<string, unknown>>();

packages/server/src/server/agent/providers/claude-agent.redesign.test.ts

@@ -412,7 +412,10 @@ test("captures session IDs from fixture-driven init message variants", async ()
     fixtures.map(async (fixture) => {
       const session = await createSession();
       const internal = session as unknown as {
-        handleSystemMessage: (message: Record<string, unknown>) => string | null;
+        handleSystemMessage: (message: Record<string, unknown>) => {
+          threadStartedSessionId: string | null;
+          notice: AgentTimelineItem | null;
+        };
       };
       try {
         const started = internal.handleSystemMessage({
@@ -422,7 +425,10 @@ test("captures session IDs from fixture-driven init message variants", async ()
           model: "opus",
           ...fixture.payload,
         });
-        expect(started).toBe(fixture.expected);
+        expect(started).toEqual({
+          threadStartedSessionId: fixture.expected,
+          notice: null,
+        });
         expect(session.describePersistence()?.sessionId).toBe(fixture.expected);
       } finally {
         await session.close();

packages/server/src/server/agent/providers/claude-agent.ts

@@ -2152,9 +2152,6 @@ class ClaudeAgentSession implements AgentSession {
       this.input = null;
       this.queryPumpPromise = null;
       this.queryRestartNeeded = false;
-      // Reset session identity for explicit restarts so the new query starts
-      // a fresh session rather than resuming the previous one.
-      this.claudeSessionId = null;
       oldInput?.end();
       oldQuery.close?.();
       try {
@@ -2164,10 +2161,8 @@ class ClaudeAgentSession implements AgentSession {
       }
     }
 
-    // When the pump died unexpectedly (query became null, e.g. after a session
-    // ID overwrite error), preserve claudeSessionId so buildOptions() passes
-    // resume: sessionId and the new query auto-resumes the previous session.
-    // For explicit restarts above, claudeSessionId was already cleared.
+    // Preserve claudeSessionId across query recreation so buildOptions() passes
+    // resume: sessionId and the new query continues the existing conversation.
     this.persistence = null;
 
     const input = createAsyncMessageInput<SDKUserMessage>();
@@ -2840,7 +2835,6 @@ class ClaudeAgentSession implements AgentSession {
       this.query = null;
       this.input = null;
     }
-    this.claudeSessionId = null;
     this.persistence = null;
     this.persistedHistory = [];
     this.historyPending = false;
@@ -2885,12 +2879,19 @@ class ClaudeAgentSession implements AgentSession {
     }
 
     const events: AgentStreamEvent[] = [];
-    const fallbackThreadSessionId = this.captureSessionIdFromMessage(message);
-    if (fallbackThreadSessionId) {
+    const sessionCapture = this.captureSessionIdFromMessage(message);
+    if (sessionCapture.notice) {
+      events.push({
+        type: "timeline",
+        provider: "claude",
+        item: sessionCapture.notice,
+      });
+    }
+    if (sessionCapture.threadStartedSessionId) {
       events.push({
         type: "thread_started",
         provider: "claude",
-        sessionId: fallbackThreadSessionId,
+        sessionId: sessionCapture.threadStartedSessionId,
       });
     }
 
@@ -2929,12 +2930,19 @@ class ClaudeAgentSession implements AgentSession {
     events: AgentStreamEvent[],
   ): void {
     if (message.subtype === "init") {
-      const threadSessionId = this.handleSystemMessage(message);
-      if (threadSessionId) {
+      const sessionUpdate = this.handleSystemMessage(message);
+      if (sessionUpdate.notice) {
+        events.push({
+          type: "timeline",
+          provider: "claude",
+          item: sessionUpdate.notice,
+        });
+      }
+      if (sessionUpdate.threadStartedSessionId) {
         events.push({
           type: "thread_started",
           provider: "claude",
-          sessionId: threadSessionId,
+          sessionId: sessionUpdate.threadStartedSessionId,
         });
       }
       return;
@@ -3091,7 +3099,20 @@ class ClaudeAgentSession implements AgentSession {
     events.push(this.buildTurnFailedEvent(errorMessage));
   }
 
-  private captureSessionIdFromMessage(message: SDKMessage): string | null {
+  private createClaudeSessionChangedNotice(
+    oldSessionId: string,
+    newSessionId: string,
+  ): AgentTimelineItem {
+    return {
+      type: "assistant_message",
+      text: `Claude switched to a new session: ${oldSessionId} -> ${newSessionId}`,
+    };
+  }
+
+  private captureSessionIdFromMessage(message: SDKMessage): {
+    threadStartedSessionId: string | null;
+    notice: AgentTimelineItem | null;
+  } {
     const msg = message as unknown as {
       session_id?: unknown;
       sessionId?: unknown;
@@ -3099,16 +3120,17 @@ class ClaudeAgentSession implements AgentSession {
     };
     const sessionId = extractSessionIdRaw(msg).trim();
     if (!sessionId) {
-      return null;
+      return { threadStartedSessionId: null, notice: null };
     }
     if (this.claudeSessionId === null) {
       this.claudeSessionId = sessionId;
       this.persistence = null;
-      return sessionId;
+      return { threadStartedSessionId: sessionId, notice: null };
     }
     if (this.claudeSessionId === sessionId) {
-      return null;
+      return { threadStartedSessionId: null, notice: null };
     }
+    const oldSessionId = this.claudeSessionId;
     // Session ID changed mid-stream (e.g. a hook caused Claude to restart
     // with a new session). Accept the new ID and continue — the turn should
     // not be failed just because the underlying subprocess cycled.
@@ -3118,12 +3140,18 @@ class ClaudeAgentSession implements AgentSession {
     );
     this.claudeSessionId = sessionId;
     this.persistence = null;
-    return sessionId;
+    return {
+      threadStartedSessionId: sessionId,
+      notice: this.createClaudeSessionChangedNotice(oldSessionId, sessionId),
+    };
   }
 
-  private handleSystemMessage(message: SDKSystemMessage): string | null {
+  private handleSystemMessage(message: SDKSystemMessage): {
+    threadStartedSessionId: string | null;
+    notice: AgentTimelineItem | null;
+  } {
     if (message.subtype !== "init") {
-      return null;
+      return { threadStartedSessionId: null, notice: null };
     }
 
     const msg = message as unknown as {
@@ -3133,10 +3161,11 @@ class ClaudeAgentSession implements AgentSession {
     };
     const newSessionId = extractSessionIdRaw(msg).trim();
     if (!newSessionId) {
-      return null;
+      return { threadStartedSessionId: null, notice: null };
     }
     const existingSessionId = this.claudeSessionId;
     let threadStartedSessionId: string | null = null;
+    let notice: AgentTimelineItem | null = null;
 
     if (existingSessionId === null) {
       this.claudeSessionId = newSessionId;
@@ -3153,6 +3182,7 @@ class ClaudeAgentSession implements AgentSession {
       );
       this.claudeSessionId = newSessionId;
       threadStartedSessionId = newSessionId;
+      notice = this.createClaudeSessionChangedNotice(existingSessionId, newSessionId);
     }
     this.availableModes = DEFAULT_MODES;
     this.currentMode = message.permissionMode;
@@ -3174,7 +3204,7 @@ class ClaudeAgentSession implements AgentSession {
       this.lastRuntimeModel = message.model;
       this.cachedRuntimeInfo = null;
     }
-    return threadStartedSessionId;
+    return { threadStartedSessionId, notice };
   }
 
   private readMissingResumedConversationError(message: SDKMessage): string | null {

packages/server/src/server/daemon-e2e/claude-thinking-memory.real.e2e.test.ts

@@ -0,0 +1,115 @@
+import { beforeAll, beforeEach, describe, expect, test } from "vitest";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import pino from "pino";
+
+import type { AgentTimelineItem } from "../agent/agent-sdk-types.js";
+import { ClaudeAgentClient } from "../agent/providers/claude-agent.js";
+import { DaemonClient } from "../test-utils/daemon-client.js";
+import { createTestPaseoDaemon } from "../test-utils/paseo-daemon.js";
+import { getFullAccessConfig, isProviderAvailable } from "./agent-configs.js";
+
+function tmpCwd(): string {
+  return mkdtempSync(path.join(tmpdir(), "daemon-real-claude-thinking-memory-"));
+}
+
+function compactText(value: string): string {
+  return value.replace(/\s+/g, "").toLowerCase();
+}
+
+function assistantMessages(items: AgentTimelineItem[]): string[] {
+  return items
+    .filter(
+      (item): item is Extract<AgentTimelineItem, { type: "assistant_message" }> =>
+        item.type === "assistant_message",
+    )
+    .map((item) => item.text);
+}
+
+function modelHasLowThinkingOption(model: {
+  id: string;
+  thinkingOptions?: Array<{ id: string }>;
+}): boolean {
+  const thinkingOptionIds = new Set(model.thinkingOptions?.map((option) => option.id) ?? []);
+  return model.id.includes("sonnet") && thinkingOptionIds.has("low");
+}
+
+async function getAssistantText(client: DaemonClient, agentId: string): Promise<string> {
+  const timeline = await client.fetchAgentTimeline(agentId, {
+    direction: "tail",
+    limit: 0,
+    projection: "canonical",
+  });
+  return assistantMessages(timeline.entries.map((entry) => entry.item)).join("\n");
+}
+
+describe("daemon E2E (real claude) - thinking effort memory", () => {
+  let canRun = false;
+
+  beforeAll(async () => {
+    canRun = await isProviderAvailable("claude");
+  });
+
+  beforeEach((context) => {
+    if (!canRun) {
+      context.skip();
+    }
+  });
+
+  test("changing thinking effort preserves the previous conversation", async () => {
+    const logger = pino({ level: "silent" });
+    const cwd = tmpCwd();
+    const daemon = await createTestPaseoDaemon({
+      agentClients: { claude: new ClaudeAgentClient({ logger }) },
+      logger,
+    });
+    const client = new DaemonClient({ url: `ws://127.0.0.1:${daemon.port}/ws` });
+
+    try {
+      await client.connect();
+      await client.fetchAgents({
+        subscribe: { subscriptionId: "claude-thinking-memory-real" },
+      });
+
+      const modelList = await client.listProviderModels("claude", { cwd });
+      const model = modelList.models.find(modelHasLowThinkingOption);
+      if (!model) {
+        throw new Error("No Claude Sonnet model with low thinking effort returned");
+      }
+
+      const agent = await client.createAgent({
+        cwd,
+        title: "claude-thinking-memory-real",
+        ...getFullAccessConfig("claude"),
+        model: model.id,
+      });
+
+      await client.sendMessage(
+        agent.id,
+        "Remember the code phrase PASEO_MEMORY_56. Reply exactly: ACK_56",
+      );
+      const firstFinish = await client.waitForFinish(agent.id, 180_000);
+      expect(firstFinish.status).toBe("idle");
+      expect(firstFinish.final?.lastError).toBeUndefined();
+      expect(compactText(await getAssistantText(client, agent.id))).toContain("ack_56");
+
+      await client.setAgentThinkingOption(agent.id, "low");
+
+      await client.sendMessage(
+        agent.id,
+        "What code phrase did I ask you to remember? Reply exactly with that code phrase and nothing else.",
+      );
+      const secondFinish = await client.waitForFinish(agent.id, 180_000);
+      expect(secondFinish.status).toBe("idle");
+      expect(secondFinish.final?.lastError).toBeUndefined();
+
+      const assistantText = await getAssistantText(client, agent.id);
+      expect(compactText(assistantText)).toContain("paseo_memory_56");
+    } finally {
+      await client.close().catch(() => undefined);
+      await daemon.close().catch(() => undefined);
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  }, 420_000);
+});