diff --git a/lib/daemon/__tests__/herd-handlers.test.ts b/lib/daemon/__tests__/herd-handlers.test.ts
index be9188e0a..4728ef044 100644
--- a/lib/daemon/__tests__/herd-handlers.test.ts
+++ b/lib/daemon/__tests__/herd-handlers.test.ts
@@ -14,11 +14,15 @@ import { createBgHandlers } from "../handlers/bg.ts";
 import { createEscapeInjector } from "../gate-escape.ts";
 import type { herdrRequest } from "../../herdr/client.ts";
 import { acceptTrustOnPane } from "../trust-accept.ts";
+import { deleteChatSession, readChatSession, writeChatSession } from "../../chat-session.ts";
 
 const log = pino({ level: "silent" });
 let dirs: string[] = [];
 beforeEach(() => { dirs = []; });
-afterEach(() => { for (const d of dirs) rmSync(d, { recursive: true, force: true }); });
+afterEach(() => {
+  for (const d of dirs) rmSync(d, { recursive: true, force: true });
+  for (const s of ["sess-w1", "sess-w2", "sess-shep", "sess-shep-2", "sess-shep-3"]) deleteChatSession(s);
+});
 
 export function harness(over: Partial<HerdDeps> = {}, trustTestBudgets: { registerBudgetMs?: number; settleMs?: number; stepMs?: number } = {}) {
   const dir = mkdtempSync(join(tmpdir(), "rt-herd-h-"));
@@ -304,6 +308,14 @@ describe("herd:resume / status / close", () => {
     return { ...hx, herd: res.data.herd, room: res.data.room };
   }
 
+  test("start and resume write the shepherd's chat session file", async () => {
+    const { h, herd } = await started();
+    expect(readChatSession("sess-shep")).toMatchObject({ handle: "shepherd", baseHandle: "shepherd" });
+    const res = await h["herd:resume"]({ herd, session: "sess-shep-2" });
+    if (!res.ok) throw new Error(res.error);
+    expect(readChatSession("sess-shep-2")).toMatchObject({ handle: "shepherd", baseHandle: "shepherd" });
+  });
+
   test("resume re-subscribes with the new session and returns gates, unread, status", async () => {
     const { h, store, gateStore, herd } = await started();
     store.upsertJob({ herd, name: "job-a", worktree: "/w/job-a", handle: "job-a", status: "active", pane: "w9:p1" });
@@ -964,6 +976,29 @@ describe("herd:spawn", () => {
     expect(readFileSync(join(dir, "herds", herd, "job-a", "job.md"), "utf8")).toContain("do the thing");
   });
 
+  test("a spawned worker gets a chat session file, so the chat_* MCP tools resolve its handle", async () => {
+    const { h, herd } = await started();
+    const res = await h["herd:spawn"]({ herd, job: "job-a", brief: "b" });
+    if (!res.ok) throw new Error(res.error);
+    expect(readChatSession("sess-w1")).toMatchObject({ sessionId: "sess-w1", handle: "job-a", baseHandle: "job-a" });
+  });
+
+  test("an existing file naming the same handle is kept, room and all", async () => {
+    writeChatSession({ sessionId: "sess-w1", handle: "job-a", baseHandle: "job-a", signedInAt: 1, room: "r" });
+    const { h, herd } = await started();
+    const res = await h["herd:spawn"]({ herd, job: "job-a", brief: "b" });
+    if (!res.ok) throw new Error(res.error);
+    expect(readChatSession("sess-w1")).toMatchObject({ handle: "job-a", room: "r", signedInAt: 1 });
+  });
+
+  test("a stale file naming another handle is rewritten to the signed-in handle, keeping its room", async () => {
+    writeChatSession({ sessionId: "sess-w1", handle: "old-2", baseHandle: "old", signedInAt: 1, room: "r" });
+    const { h, herd } = await started();
+    const res = await h["herd:spawn"]({ herd, job: "job-a", brief: "b" });
+    if (!res.ok) throw new Error(res.error);
+    expect(readChatSession("sess-w1")).toMatchObject({ handle: "job-a", baseHandle: "job-a", room: "r" });
+  });
+
   test("--dir skips provisioning; a respawn closes the old pane first and reuses the stored job.md", async () => {
     const { h, store, agentCalls, worktreeCalls, herdrCalls, herd } = await started();
     const first = await h["herd:spawn"]({ herd, job: "job-a", brief: "the brief", dir: "/existing/tree" });
diff --git a/lib/daemon/handlers/herd.ts b/lib/daemon/handlers/herd.ts
index 6921d75d2..135332dcc 100644
--- a/lib/daemon/handlers/herd.ts
+++ b/lib/daemon/handlers/herd.ts
@@ -20,6 +20,7 @@ import type { createAgentHandlers } from "./agent.ts";
 import type { herdrRequest } from "../../herdr/client.ts";
 import type { HerdrRunner } from "../../agent-herdr.ts";
 import { slugifyChatName } from "../../chat-room-name.ts";
+import { readChatSession, writeChatSession } from "../../chat-session.ts";
 import { attendPane } from "../attend.ts";
 import type { TrustOutcome } from "../trust-accept.ts";
 import { BG_SESSION } from "../bg-service.ts";
@@ -69,6 +70,21 @@ export const MILESTONE_OPTIONS = ["Approve", "Revise", "Spawn a reviewer"] as co
     rich option text through the shared gate store, so this cap never moves
     into gate:open or normalizeGateQuestions. */
 export const HERD_OPTION_LABEL_MAX = 60;
+
+/** The chat_* MCP tools resolve identity only from the session file, which
+    only the CLI's sign-in writes; a session the daemon signed in has no file
+    unless it is written here. A file already naming this handle is kept (it
+    may carry the CLI's room and cwd); one naming another handle is stale and
+    would make every chat_* call act as a handle the session no longer owns. */
+function recordChatSession(log: Logger, sessionId: string, handle: string, baseHandle: string): void {
+  try {
+    const existing = readChatSession(sessionId);
+    if (existing?.handle === handle) return;
+    writeChatSession({ ...existing, sessionId, handle, baseHandle, signedInAt: Date.now() });
+  } catch (err) {
+    log.warn({ err, sessionId }, "herd: could not write the chat session file; chat_* tools will not resolve this session");
+  }
+}
 const RECOMMENDED_TAIL = /\s*\(\s*recommended\s*\)\s*$/i;
 
 function overlongOptionLabel(questions: GateQuestion[]): string | undefined {
@@ -293,6 +309,7 @@ export function createHerdHandlers(deps: HerdDeps) {
         if (!signIn.ok) return signIn;
         handle = signIn.data.handle;
       }
+      recordChatSession(log, session, handle, SHEPHERD_HANDLE);
       const join = await deps.chat["chat:join"]({ room, handle });
       if (!join.ok) return join;
 
@@ -325,6 +342,7 @@ export function createHerdHandlers(deps: HerdDeps) {
         if (!signIn.ok) return signIn;
         handle = signIn.data.handle;
       }
+      recordChatSession(log, session, handle, baseHandleOf(herd.shepherdHandle));
       const join = await deps.chat["chat:join"]({ room: herd.room, handle });
       if (!join.ok) return join;
       store.setShepherd(herdId, { session, handle, pane: p?.callerPane ?? null });
@@ -433,6 +451,7 @@ export function createHerdHandlers(deps: HerdDeps) {
       const signIn = await deps.chat["chat:sign-in"]({ sessionId: rec.sessionId, baseHandle: name, pane: rec.paneId, cwd: worktree, noRoom: true });
       if (!signIn.ok) log.warn({ herd: herdId, job: name, error: signIn.error }, "herd: worker chat sign-in failed; reports will not deliver until it signs in");
       const handle = signIn.ok ? signIn.data.handle : name;
+      if (signIn.ok) recordChatSession(log, rec.sessionId, handle, signIn.data.baseHandle);
       const joined = await deps.chat["chat:join"]({ room: herd.room, handle, pane: rec.paneId, cwd: worktree });
       if (!joined.ok) log.warn({ herd: herdId, job: name, error: joined.error }, "herd: worker room join failed");
       if (handle !== name) store.upsertJob({ herd: herdId, name, worktree, branch, tree, handle, status: "spawning" });