feat(node): add Claude Code UserPromptSubmit hook for auto inbox-check

Adds `install-hook` / `uninstall-hook` subcommands that idempotently patch
~/.claude/settings.json (or .claude/settings.json with --project), plus a
`--hook` flag on `check` that emits human-readable output and stays silent
on empty inbox or unreachable daemon.

node/src/cli.ts

@@ -1,11 +1,22 @@
 #!/usr/bin/env node
 import { Command } from "commander";
-import { readFileSync } from "node:fs";
+import { existsSync, readFileSync } from "node:fs";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 import { resolveConfig, baseUrl, DEFAULT_PORT } from "./config.js";
 import { startServer } from "./server.js";
 import { autostartManager } from "./autostart/index.js";
+import {
+  applyInstall,
+  applyUninstall,
+  buildHookCommand,
+  formatMessagesForHook,
+  readSettings,
+  settingsPathFor,
+  writeSettings,
+  type HookMessage,
+  type HookScope,
+} from "./hook.js";
 
 function readVersion(): string {
   try {
@@ -119,15 +130,26 @@ program
   .description("Pull pending messages and mark delivered.")
   .requiredOption("--name <name>", "Mailbox name (also sent as X-Mailbox)")
   .option("--url <url>", "Daemon base URL", DEFAULT_URL)
-  .action(async (opts: { name: string; url: string }) => {
+  .option(
+    "--hook",
+    "Hook mode: human-readable output, silent on empty inbox or unreachable daemon (exit 0)",
+  )
+  .action(async (opts: { name: string; url: string; hook?: boolean }) => {
     try {
       const out = await callJson(
         "POST",
         `${opts.url}/v1/check-inbox?name=${encodeURIComponent(opts.name)}`,
         { headers: { "X-Mailbox": opts.name } },
       );
+      if (opts.hook) {
+        const messages = (Array.isArray(out) ? out : []) as HookMessage[];
+        const text = formatMessagesForHook(opts.name, messages);
+        if (text) process.stdout.write(text);
+        return;
+      }
       console.log(JSON.stringify(out, null, 2));
     } catch (err) {
+      if (opts.hook) return;
       reportClientError(err, opts.url);
     }
   });
@@ -145,6 +167,60 @@ program
     }
   });
 
+program
+  .command("install-hook")
+  .description(
+    "Install a Claude Code UserPromptSubmit hook that checks the mailbox on every prompt. Idempotent.",
+  )
+  .requiredOption("--name <name>", "Mailbox name to check")
+  .option("--user", "Patch ~/.claude/settings.json (default)")
+  .option("--project", "Patch <cwd>/.claude/settings.json")
+  .option("--url <url>", "Daemon base URL to embed in the hook command")
+  .action(async (opts: { name: string; user?: boolean; project?: boolean; url?: string }) => {
+    if (opts.user && opts.project) {
+      console.error("Pick either --user or --project, not both.");
+      process.exit(1);
+    }
+    const scope: HookScope = opts.project ? "project" : "user";
+    const path = settingsPathFor(scope);
+    const settings = readSettings(path);
+    const command = buildHookCommand(opts.name, opts.url);
+    const result = applyInstall(settings, command);
+    if (result.changed) {
+      writeSettings(path, settings);
+      console.log(`Hook installed in ${path}`);
+      console.log(`Command: ${command}`);
+    } else {
+      console.log(`Hook already present in ${path}; nothing to do.`);
+    }
+  });
+
+program
+  .command("uninstall-hook")
+  .description("Remove the claude-mailbox UserPromptSubmit hook from Claude Code settings.")
+  .option("--user", "Patch ~/.claude/settings.json (default)")
+  .option("--project", "Patch <cwd>/.claude/settings.json")
+  .action(async (opts: { user?: boolean; project?: boolean }) => {
+    if (opts.user && opts.project) {
+      console.error("Pick either --user or --project, not both.");
+      process.exit(1);
+    }
+    const scope: HookScope = opts.project ? "project" : "user";
+    const path = settingsPathFor(scope);
+    if (!existsSync(path)) {
+      console.log(`No settings file at ${path}; nothing to remove.`);
+      return;
+    }
+    const settings = readSettings(path);
+    const result = applyUninstall(settings);
+    if (result.changed) {
+      writeSettings(path, settings);
+      console.log(`Hook removed from ${path}`);
+    } else {
+      console.log(`No claude-mailbox hook found in ${path}; nothing to remove.`);
+    }
+  });
+
 program
   .command("install-autostart")
   .description(