diff --git a/src/server/create-server.test.ts b/src/server/create-server.test.ts
index 58d3884..999d0ec 100644
--- a/src/server/create-server.test.ts
+++ b/src/server/create-server.test.ts
@@ -1728,3 +1728,163 @@ describe('observation compaction in HTTP responses', () => {
     expect(body.observations).toBeUndefined();
   });
 });
+
+describe('ToolHooks', () => {
+  let server: ServerInstance;
+  let state: DaemonState;
+  let hooks: {
+    onToolStart: ReturnType<typeof vi.fn>;
+    onToolEnd: ReturnType<typeof vi.fn>;
+    onToolError: ReturnType<typeof vi.fn>;
+    onSessionStart: ReturnType<typeof vi.fn>;
+    onSessionEnd: ReturnType<typeof vi.fn>;
+    onServerStart: ReturnType<typeof vi.fn>;
+    onServerStop: ReturnType<typeof vi.fn>;
+  };
+
+  beforeEach(async () => {
+    await fs.mkdir(tmpDir, { recursive: true });
+    hooks = {
+      onToolStart: vi.fn(),
+      onToolEnd: vi.fn(),
+      onToolError: vi.fn(),
+      onSessionStart: vi.fn(),
+      onSessionEnd: vi.fn(),
+      onServerStart: vi.fn(),
+      onServerStop: vi.fn(),
+    };
+    server = createServer(buildConfig({ hooks }));
+    state = await server.start();
+  });
+
+  afterEach(async () => {
+    await server.stop();
+    await fs.rm(tmpDir, { recursive: true, force: true }).catch(() => {});
+  });
+
+  it('calls onServerStart after daemon starts', () => {
+    expect(hooks.onServerStart).toHaveBeenCalledWith(
+      expect.objectContaining({ port: state.port, pid: process.pid }),
+    );
+  });
+
+  it('calls onServerStop during shutdown', async () => {
+    await server.stop();
+    expect(hooks.onServerStop).toHaveBeenCalled();
+  });
+
+  it('calls onToolStart and onToolEnd for a successful tool call', async () => {
+    await httpRequest(`http://127.0.0.1:${state.port}/tool/get_context`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({}),
+    });
+
+    expect(hooks.onToolStart).toHaveBeenCalledWith(
+      expect.objectContaining({ toolName: 'get_context' }),
+    );
+    expect(hooks.onToolEnd).toHaveBeenCalledWith(
+      expect.objectContaining({
+        toolName: 'get_context',
+        ok: true,
+        durationMs: expect.any(Number),
+      }),
+    );
+  });
+
+  it('calls onToolEnd with ok=false when a tool returns an error', async () => {
+    const failingManager = createMockSessionManager();
+    failingManager.hasActiveSession.mockReturnValue(true);
+    failingManager.cleanup.mockResolvedValue(false);
+
+    const failServer = createServer(
+      buildConfig({
+        hooks,
+        sessionManager:
+          failingManager as unknown as ServerConfig['sessionManager'],
+      }),
+    );
+    const failState = await failServer.start();
+
+    failingManager.launch.mockRejectedValue(new Error('launch exploded'));
+    await httpRequest(`http://127.0.0.1:${failState.port}/launch`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ force: true }),
+    });
+
+    expect(hooks.onToolEnd).toHaveBeenCalledWith(
+      expect.objectContaining({
+        toolName: 'launch',
+        ok: false,
+      }),
+    );
+
+    await failServer.stop();
+  });
+
+  it('calls onSessionStart after a successful launch', async () => {
+    await httpRequest(`http://127.0.0.1:${state.port}/launch`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({}),
+    });
+
+    expect(hooks.onSessionStart).toHaveBeenCalledWith(
+      'test-session',
+      expect.any(Object),
+    );
+  });
+
+  it('calls onSessionEnd after cleanup', async () => {
+    await httpRequest(`http://127.0.0.1:${state.port}/cleanup`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({}),
+    });
+
+    expect(hooks.onSessionEnd).toHaveBeenCalledWith('test-session');
+  });
+
+  it('does not break tool execution when a hook throws', async () => {
+    hooks.onToolStart.mockImplementation(() => {
+      throw new Error('hook exploded');
+    });
+    hooks.onToolEnd.mockImplementation(() => {
+      throw new Error('hook exploded');
+    });
+
+    const res = await httpRequest(
+      `http://127.0.0.1:${state.port}/tool/get_context`,
+      {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({}),
+      },
+    );
+    const body = (await res.json()) as { ok: boolean };
+
+    expect(res.status).toBe(200);
+    expect(body.ok).toBe(true);
+  });
+
+  it('works identically when hooks is undefined', async () => {
+    const noHookServer = createServer(buildConfig());
+    const noHookState = await noHookServer.start();
+
+    const res = await httpRequest(
+      `http://127.0.0.1:${noHookState.port}/tool/get_context`,
+      {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({}),
+      },
+    );
+    const body = (await res.json()) as { ok: boolean };
+
+    expect(res.status).toBe(200);
+    expect(body.ok).toBe(true);
+
+    await noHookServer.stop();
+  });
+});
diff --git a/src/server/create-server.ts b/src/server/create-server.ts
index 3c1e893..7ca979c 100644
--- a/src/server/create-server.ts
+++ b/src/server/create-server.ts
@@ -281,6 +281,10 @@ export function createServer(config: ServerConfig): ServerInstance {
         uptime: process.uptime(),
         startedAt,
       },
+      session: {
+        active: config.sessionManager.hasActiveSession(),
+        id: config.sessionManager.getSessionId() ?? null,
+      },
       ports: subPorts,
     });
   });
@@ -424,8 +428,11 @@ export function createServer(config: ServerConfig): ServerInstance {
 
     const startTime = Date.now();
     const currentWorkflowContext = workflowContext;
-
     const category = getToolCategory(toolName);
+    const sessionId = config.sessionManager.getSessionId();
+    const hookCtx = { toolName, input: validatedInput, sessionId, category };
+
+    try { config.hooks?.onToolStart?.(hookCtx); } catch { /* fire-and-forget */ }
 
     try {
       const { toolResult, observations } = await queue.enqueue(async () => {
@@ -499,6 +506,8 @@ export function createServer(config: ServerConfig): ServerInstance {
         return { toolResult: result, observations: obs };
       });
 
+      const durationMs = Date.now() - startTime;
+
       await recordToolStep(
         toolName,
         validatedInput,
@@ -508,6 +517,31 @@ export function createServer(config: ServerConfig): ServerInstance {
         startTime,
       );
 
+      try {
+        config.hooks?.onToolEnd?.({
+          ...hookCtx,
+          result: toolResult,
+          durationMs,
+          ok: Boolean((toolResult as { ok?: boolean }).ok),
+        });
+      } catch { /* fire-and-forget */ }
+
+      if (toolName === 'launch' && (toolResult as { ok?: boolean }).ok) {
+        const launchSessionId = config.sessionManager.getSessionId();
+        if (launchSessionId) {
+          try {
+            config.hooks?.onSessionStart?.(
+              launchSessionId,
+              validatedInput as Record<string, unknown>,
+            );
+          } catch { /* fire-and-forget */ }
+        }
+      }
+
+      if (toolName === 'cleanup' && sessionId) {
+        try { config.hooks?.onSessionEnd?.(sessionId); } catch { /* fire-and-forget */ }
+      }
+
       const includeInResponse = shouldIncludeObservationsInResponse(
         category,
         toolResult,
@@ -529,6 +563,9 @@ export function createServer(config: ServerConfig): ServerInstance {
         lastObservation = observations;
       }
     } catch (error) {
+      const errorDurationMs = Date.now() - startTime;
+      const errorMessage = extractErrorMessage(error);
+
       await recordToolStep(
         toolName,
         validatedInput,
@@ -536,7 +573,7 @@ export function createServer(config: ServerConfig): ServerInstance {
           ok: false,
           error: {
             code: 'TOOL_EXECUTION_FAILED',
-            message: extractErrorMessage(error),
+            message: errorMessage,
           },
         },
         undefined,
@@ -544,11 +581,19 @@ export function createServer(config: ServerConfig): ServerInstance {
         startTime,
       );
 
+      try {
+        config.hooks?.onToolError?.({
+          ...hookCtx,
+          error: errorMessage,
+          durationMs: errorDurationMs,
+        });
+      } catch { /* fire-and-forget */ }
+
       res.status(500).json({
         ok: false,
         error: {
           code: 'TOOL_EXECUTION_FAILED',
-          message: extractErrorMessage(error),
+          message: errorMessage,
         },
       });
     }
@@ -701,6 +746,8 @@ export function createServer(config: ServerConfig): ServerInstance {
           idleCheckInterval.unref();
         }
 
+        try { config.hooks?.onServerStart?.(state); } catch { /* fire-and-forget */ }
+
         return state;
       } catch (startupError) {
         // Best-effort rollback: close the HTTP server if it was created,
@@ -734,6 +781,8 @@ export function createServer(config: ServerConfig): ServerInstance {
 
       appendLog(config.logFilePath, '[INFO] Daemon shutting down');
 
+      try { config.hooks?.onServerStop?.(); } catch { /* fire-and-forget */ }
+
       // 1. Remove signal handlers
       if (shutdownHandler) {
         process.removeListener('SIGTERM', shutdownHandler);
diff --git a/src/types/http.ts b/src/types/http.ts
index d1cac1c..70fb077 100644
--- a/src/types/http.ts
+++ b/src/types/http.ts
@@ -54,6 +54,43 @@ export type ToolFunction<TParams = unknown, TResult = unknown> = (
   context: ToolContext,
 ) => Promise<ToolResponse<TResult>>;
 
+export type ToolHookContext = {
+  toolName: string;
+  input: unknown;
+  sessionId: string | undefined;
+  category: string;
+};
+
+/**
+ * Lifecycle hooks for observability and tracing.
+ *
+ * All hooks are fire-and-forget — errors are silently caught and never
+ * block tool execution or HTTP responses.
+ */
+export type ToolHooks = {
+  onToolStart?: (ctx: ToolHookContext) => void | Promise<void>;
+  onToolEnd?: (
+    ctx: ToolHookContext & {
+      result: unknown;
+      durationMs: number;
+      ok: boolean;
+    },
+  ) => void | Promise<void>;
+  onToolError?: (
+    ctx: ToolHookContext & {
+      error: string;
+      durationMs: number;
+    },
+  ) => void | Promise<void>;
+  onSessionStart?: (
+    sessionId: string,
+    metadata: Record<string, unknown>,
+  ) => void | Promise<void>;
+  onSessionEnd?: (sessionId: string) => void | Promise<void>;
+  onServerStart?: (state: DaemonState) => void | Promise<void>;
+  onServerStop?: () => void | Promise<void>;
+};
+
 /**
  * Configuration for createServer().
  *
@@ -73,6 +110,8 @@ export type ServerConfig = {
   requestTimeoutMs?: number;
   /** Path to log file (optional) */
   logFilePath?: string;
+  /** Optional lifecycle hooks for observability (e.g. Langfuse, OpenTelemetry) */
+  hooks?: ToolHooks;
 };
 
 /**