feat(plugin): per-session mailbox identity + mailbox-update command

The hook now derives a unique mailbox name from the session_id supplied
on hook stdin, so two parallel Claude Code sessions in the same project
get distinct mailboxes (e.g. `claude-a8b3c1d2`, `claude-d4e5f6a7`)
instead of colliding on a shared env value. An optional
CLAUDE_MAILBOX_NAME base prefix flavors the names as `<base>-<sid>`.

Adds:
- `claude-mailbox session-announce` subcommand for the new SessionStart
  hook, which prints the current session's mailbox name to context
- `/claude-mailbox:mailbox-update` slash command for `npm update` +
  daemon restart
- stdin parsing helpers (parseHookStdin, deriveSessionName) with unit
  tests; the doctor no longer needs a mandatory name prompt

node/tests/cli-hook.test.ts

@@ -5,14 +5,14 @@ import { resolve } from "node:path";
 
 const cliPath = resolve(__dirname, "..", "dist", "cli.js");
 
-function runCli(args: string[], env: Record<string, string | undefined> = {}): {
-  status: number;
-  stdout: string;
-  stderr: string;
-} {
+function runCli(
+  args: string[],
+  opts: { env?: Record<string, string | undefined>; stdin?: string } = {},
+): { status: number; stdout: string; stderr: string } {
   const r = spawnSync(process.execPath, [cliPath, ...args], {
     encoding: "utf8",
-    env: { ...process.env, ...env },
+    env: { ...process.env, ...(opts.env ?? {}) },
+    input: opts.stdin,
   });
   return {
     status: r.status ?? -1,
@@ -21,6 +21,13 @@ function runCli(args: string[], env: Record<string, string | undefined> = {}): {
   };
 }
 
+const HOOK_STDIN = JSON.stringify({
+  session_id: "abc12345-de67-89f0-1234-567890abcdef",
+  hook_event_name: "UserPromptSubmit",
+  cwd: "/tmp",
+  prompt: "test",
+});
+
 describe("`check --hook` CLI behavior", () => {
   beforeAll(() => {
     if (!existsSync(cliPath)) {
@@ -28,36 +35,87 @@ describe("`check --hook` CLI behavior", () => {
     }
   });
 
-  it("exits 0 silently when no name resolved (no --name, no env)", () => {
-    const r = runCli(["check", "--hook"], { CLAUDE_MAILBOX_NAME: undefined });
+  it("exits 0 silently when no stdin, no --name, no env", () => {
+    const r = runCli(["check", "--hook"], { env: { CLAUDE_MAILBOX_NAME: undefined } });
     expect(r.status).toBe(0);
     expect(r.stdout).toBe("");
     expect(r.stderr).toBe("");
   });
 
-  it("emits daemon-not-reachable hint when name is set but daemon is down", () => {
-    const r = runCli(
-      ["check", "--hook", "--url", "http://127.0.0.1:1"],
-      { CLAUDE_MAILBOX_NAME: "alice" },
-    );
+  it("derives session-id-based name from stdin and emits daemon hint when down", () => {
+    const r = runCli(["check", "--hook", "--url", "http://127.0.0.1:1"], {
+      env: { CLAUDE_MAILBOX_NAME: undefined },
+      stdin: HOOK_STDIN,
+    });
     expect(r.status).toBe(0);
     expect(r.stdout).toContain("[Claude-Mailbox] Daemon not reachable");
-    expect(r.stdout).toContain("http://127.0.0.1:1");
-    expect(r.stdout).toContain("claude-mailbox install-autostart");
   });
 
-  it("`--name` arg wins over CLAUDE_MAILBOX_NAME env (visible via hint URL/contents)", () => {
+  it("uses base prefix from CLAUDE_MAILBOX_NAME when both env and stdin present", () => {
+    // We can't directly assert the name from --hook output (it's only in the unreachable hint URL).
+    // The hint always contains the URL we passed, so this just confirms the path runs without error.
+    const r = runCli(["check", "--hook", "--url", "http://127.0.0.1:1"], {
+      env: { CLAUDE_MAILBOX_NAME: "backend" },
+      stdin: HOOK_STDIN,
+    });
+    expect(r.status).toBe(0);
+    expect(r.stdout).toContain("[Claude-Mailbox] Daemon not reachable");
+  });
+
+  it("explicit --name overrides session-id derivation", () => {
     const r = runCli(
-      ["check", "--hook", "--name", "bob", "--url", "http://127.0.0.1:1"],
-      { CLAUDE_MAILBOX_NAME: "alice" },
+      ["check", "--hook", "--name", "explicit", "--url", "http://127.0.0.1:1"],
+      { env: { CLAUDE_MAILBOX_NAME: "ignored" }, stdin: HOOK_STDIN },
     );
     expect(r.status).toBe(0);
     expect(r.stdout).toContain("[Claude-Mailbox] Daemon not reachable");
   });
 
   it("non-hook mode errors out when no name resolved", () => {
-    const r = runCli(["check"], { CLAUDE_MAILBOX_NAME: undefined });
+    const r = runCli(["check"], { env: { CLAUDE_MAILBOX_NAME: undefined } });
     expect(r.status).not.toBe(0);
     expect(r.stderr).toContain("CLAUDE_MAILBOX_NAME");
   });
 });
+
+describe("`session-announce` CLI behavior", () => {
+  beforeAll(() => {
+    if (!existsSync(cliPath)) {
+      throw new Error(`CLI not built. Run \`npm run build\` first. Missing: ${cliPath}`);
+    }
+  });
+
+  it("prints the derived mailbox name from a SessionStart payload", () => {
+    const r = runCli(["session-announce"], {
+      env: { CLAUDE_MAILBOX_NAME: undefined },
+      stdin: HOOK_STDIN,
+    });
+    expect(r.status).toBe(0);
+    expect(r.stdout).toContain("`claude-abc12345`");
+    expect(r.stdout).toContain("claude-mailbox send");
+  });
+
+  it("uses base prefix when set", () => {
+    const r = runCli(["session-announce"], {
+      env: { CLAUDE_MAILBOX_NAME: "backend" },
+      stdin: HOOK_STDIN,
+    });
+    expect(r.status).toBe(0);
+    expect(r.stdout).toContain("`backend-abc12345`");
+  });
+
+  it("stays silent when no session_id in stdin", () => {
+    const r = runCli(["session-announce"], {
+      env: { CLAUDE_MAILBOX_NAME: undefined },
+      stdin: JSON.stringify({ hook_event_name: "SessionStart" }),
+    });
+    expect(r.status).toBe(0);
+    expect(r.stdout).toBe("");
+  });
+
+  it("stays silent when no stdin at all", () => {
+    const r = runCli(["session-announce"], { env: { CLAUDE_MAILBOX_NAME: undefined } });
+    expect(r.status).toBe(0);
+    expect(r.stdout).toBe("");
+  });
+});