feat(gateway): live-stream /update output + forward interactive prompts

Adds real-time output streaming and interactive prompt forwarding for
the gateway /update command, so users on Telegram/Discord/etc see the
full update progress and can respond to prompts (stash restore, config
migration) without needing terminal access.

Changes:

hermes_cli/main.py:
- Add --gateway flag to 'hermes update' argparse
- Add _gateway_prompt() file-based IPC function that writes
  .update_prompt.json and polls for .update_response
- Modify _restore_stashed_changes() to accept optional input_fn
  parameter for gateway mode prompt forwarding
- cmd_update() uses _gateway_prompt when --gateway is set, enabling
  interactive stash restore and config migration prompts

gateway/run.py:
- _handle_update_command: spawn with --gateway flag and
  PYTHONUNBUFFERED=1 for real-time output flushing
- Store session_key in .update_pending.json for cross-restart
  session matching
- Add _update_prompt_pending dict to track sessions awaiting
  update prompt responses
- Replace _watch_for_update_completion with _watch_update_progress:
  streams output chunks every ~4s, detects .update_prompt.json and
  forwards prompts to the user, handles completion/failure/timeout
- Add update prompt interception in _handle_message: when a prompt
  is pending, the user's next message is written to .update_response
  instead of being processed normally
- Preserve _send_update_notification as legacy fallback for
  post-restart cases where adapter isn't available yet

File-based IPC protocol:
- .update_prompt.json: written by update process with prompt text,
  default value, and unique ID
- .update_response: written by gateway with user's answer
- .update_output.txt: existing, now streamed in real-time
- .update_exit_code: existing completion marker

Tests: 16 new tests covering _gateway_prompt IPC, output streaming,
prompt detection/forwarding, message interception, and cleanup.

hermes_cli/main.py

@@ -2554,6 +2554,57 @@ def _clear_bytecode_cache(root: Path) -> int:
     return removed
 
 
+def _gateway_prompt(prompt_text: str, default: str = "", timeout: float = 300.0) -> str:
+    """File-based IPC prompt for gateway mode.
+
+    Writes a prompt marker file so the gateway can forward the question to the
+    user, then polls for a response file.  Falls back to *default* on timeout.
+
+    Used by ``hermes update --gateway`` so interactive prompts (stash restore,
+    config migration) are forwarded to the messenger instead of being silently
+    skipped.
+    """
+    import json as _json
+    import uuid as _uuid
+    from hermes_constants import get_hermes_home
+
+    home = get_hermes_home()
+    prompt_path = home / ".update_prompt.json"
+    response_path = home / ".update_response"
+
+    # Clean any stale response file
+    response_path.unlink(missing_ok=True)
+
+    payload = {
+        "prompt": prompt_text,
+        "default": default,
+        "id": str(_uuid.uuid4()),
+    }
+    tmp = prompt_path.with_suffix(".tmp")
+    tmp.write_text(_json.dumps(payload))
+    tmp.replace(prompt_path)
+
+    # Poll for response
+    import time as _time
+    deadline = _time.monotonic() + timeout
+    while _time.monotonic() < deadline:
+        if response_path.exists():
+            try:
+                answer = response_path.read_text().strip()
+                response_path.unlink(missing_ok=True)
+                prompt_path.unlink(missing_ok=True)
+                return answer if answer else default
+            except (OSError, ValueError):
+                pass
+        _time.sleep(0.5)
+
+    # Timeout — clean up and use default
+    prompt_path.unlink(missing_ok=True)
+    response_path.unlink(missing_ok=True)
+    print(f"  (no response after {int(timeout)}s, using default: {default!r})")
+    return default
+
+
 def _update_via_zip(args):
     """Update Hermes Agent by downloading a ZIP archive.
     
@@ -2747,6 +2798,7 @@ def _restore_stashed_changes(
     cwd: Path,
     stash_ref: str,
     prompt_user: bool = False,
+    input_fn=None,
 ) -> bool:
     if prompt_user:
         print()
@@ -2754,7 +2806,10 @@ def _restore_stashed_changes(
         print("  Restoring them may reapply local customizations onto the updated codebase.")
         print("  Review the result afterward if Hermes behaves unexpectedly.")
         print("Restore local changes now? [Y/n]")
-        response = input().strip().lower()
+        if input_fn is not None:
+            response = input_fn("Restore local changes now? [Y/n]", "y")
+        else:
+            response = input().strip().lower()
         if response not in ("", "y", "yes"):
             print("Skipped restoring local changes.")
             print("Your changes are still preserved in git stash.")
@@ -3185,6 +3240,10 @@ def cmd_update(args):
     if is_managed():
         managed_error("update Hermes Agent")
         return
+
+    gateway_mode = getattr(args, "gateway", False)
+    # In gateway mode, use file-based IPC for prompts instead of stdin
+    gw_input_fn = (lambda prompt, default="": _gateway_prompt(prompt, default)) if gateway_mode else None
     
     print("⚕ Updating Hermes Agent...")
     print()
@@ -3281,7 +3340,9 @@ def cmd_update(args):
         else:
             auto_stash_ref = _stash_local_changes_if_needed(git_cmd, PROJECT_ROOT)
 
-        prompt_for_restore = auto_stash_ref is not None and sys.stdin.isatty() and sys.stdout.isatty()
+        prompt_for_restore = auto_stash_ref is not None and (
+            gateway_mode or (sys.stdin.isatty() and sys.stdout.isatty())
+        )
 
         # Check if there are updates
         result = subprocess.run(
@@ -3300,6 +3361,7 @@ def cmd_update(args):
                 _restore_stashed_changes(
                     git_cmd, PROJECT_ROOT, auto_stash_ref,
                     prompt_user=prompt_for_restore,
+                    input_fn=gw_input_fn,
                 )
             if current_branch not in ("main", "HEAD"):
                 subprocess.run(
@@ -3351,6 +3413,7 @@ def cmd_update(args):
                         PROJECT_ROOT,
                         auto_stash_ref,
                         prompt_user=prompt_for_restore,
+                        input_fn=gw_input_fn,
                     )
         
         _invalidate_update_cache()
@@ -3490,7 +3553,11 @@ def cmd_update(args):
                 print(f"  ℹ️  {len(missing_config)} new config option(s) available")
             
             print()
-            if not (sys.stdin.isatty() and sys.stdout.isatty()):
+            if gateway_mode:
+                response = _gateway_prompt(
+                    "Would you like to configure new options now? [Y/n]", "n"
+                ).strip().lower()
+            elif not (sys.stdin.isatty() and sys.stdout.isatty()):
                 print("  ℹ Non-interactive session — skipping config migration prompt.")
                 print("    Run 'hermes config migrate' later to apply any new config/env options.")
                 response = "n"
@@ -3502,11 +3569,15 @@ def cmd_update(args):
             
             if response in ('', 'y', 'yes'):
                 print()
-                results = migrate_config(interactive=True, quiet=False)
+                # In gateway mode, run auto-migrations only (no input() prompts
+                # for API keys which would hang the detached process).
+                results = migrate_config(interactive=not gateway_mode, quiet=False)
                 
                 if results["env_added"] or results["config_added"]:
                     print()
                     print("✓ Configuration updated!")
+                if gateway_mode and missing_env:
+                    print("  ℹ API keys require manual entry: hermes config migrate")
             else:
                 print()
                 print("Skipped. Run 'hermes config migrate' later to configure.")
@@ -5247,6 +5318,10 @@ For more help on a command:
         help="Update Hermes Agent to the latest version",
         description="Pull the latest changes from git and reinstall dependencies"
     )
+    update_parser.add_argument(
+        "--gateway", action="store_true", default=False,
+        help="Gateway mode: use file-based IPC for prompts instead of stdin (used internally by /update)"
+    )
     update_parser.set_defaults(func=cmd_update)
     
     # =========================================================================