feat(hook): nudge Claude to start watch --block as background bash on session start

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

node/tests/hook.test.ts

@@ -7,6 +7,7 @@ import {
   applyInstall,
   applyUninstall,
   buildHookCommand,
+  buildSessionAnnounceLines,
   deriveProjectName,
   deriveSessionName,
   formatActivePeerList,
@@ -359,6 +360,50 @@ describe("formatActivePeerList", () => {
   });
 });
 
+describe("buildSessionAnnounceLines", () => {
+  it("includes the identity announcement and tool-call examples", () => {
+    const out = buildSessionAnnounceLines({
+      name: "alice-abc12345",
+      peers: [],
+      windowMinutes: 60,
+      maxPeers: 10,
+    }).join("\n");
+    expect(out).toContain("alice-abc12345");
+    expect(out).toContain("mcp__mailbox__send");
+  });
+
+  it("includes the watcher bootstrap instruction when watcherCommand is set", () => {
+    const out = buildSessionAnnounceLines({
+      name: "alice-abc12345",
+      peers: [],
+      windowMinutes: 60,
+      maxPeers: 10,
+      watcherCommand: "claude-mailbox watch --block --name alice-abc12345",
+    }).join("\n");
+    expect(out).toContain("watch --block --name alice-abc12345");
+    expect(out).toContain("run_in_background=true");
+    expect(out).toMatch(/\[Claude-Mailbox\] Mail from/);
+    // Strong-directive framing: must be a REQUIRED FIRST ACTION, not a soft tip.
+    expect(out).toMatch(/REQUIRED FIRST ACTION/);
+    expect(out).toMatch(/MUST launch/);
+    // Relaunch protocol must cover every exit code Claude will see.
+    expect(out).toMatch(/exit code 3/);
+    expect(out).toMatch(/exit code 2/);
+    expect(out).toMatch(/renamed to/);
+  });
+
+  it("omits the watcher instruction when watcherCommand is unset", () => {
+    const out = buildSessionAnnounceLines({
+      name: "alice-abc12345",
+      peers: [],
+      windowMinutes: 60,
+      maxPeers: 10,
+    }).join("\n");
+    expect(out).not.toContain("watch --block");
+    expect(out).not.toContain("run_in_background");
+  });
+});
+
 describe("readSettings / writeSettings roundtrip", () => {
   it("survives an install → write → read cycle", () => {
     const dir = mkdtempSync(join(tmpdir(), "claude-mailbox-hook-"));