feat(gateway): opt-in runtime-metadata footer on final replies (#17026)

Append a compact 'model · 68% · ~/projects/hermes' footer to the FINAL
message of each turn, disabled by default (display.runtime_footer.enabled).
Answers the Telegram-side parity ask: runtime context that the CLI status
bar already shows is now available in messaging replies when enabled.

Wiring:
- gateway/runtime_footer.py: resolve_footer_config + format_runtime_footer +
  build_footer_line. Pure-function renderer; per-platform overrides under
  display.platforms.<platform>.runtime_footer.
- gateway/run.py: appends footer to response right after reasoning prepend
  so it lands only on the final message (never tool progress or streaming
  chunks). When streaming already delivered the body (already_sent), the
  footer is sent as a small trailing message instead.
- agent_result now exposes context_length alongside last_prompt_tokens so
  the footer can compute the pct; both gateway return paths updated.
- /footer [on|off|status] slash command, wired in CLI (cli.py) and gateway
  (gateway/run.py both running-agent bypass and main dispatch). Global
  toggle only; per-platform overrides via config.yaml.

Graceful degradation:
- Missing context_length (unknown model) → pct field silently dropped
  (no '?%' artifact).
- Empty final_response → no footer appended.
- Unknown field names in config → silently ignored.

Tests: 25-case unit suite (tests/gateway/test_runtime_footer.py) plus E2E
harness covering streaming vs non-streaming branches, per-platform override,
and the exact argument contract gateway/run.py uses.

Co-authored-by: teknium1 <teknium@users.noreply.github.com>

cli.py

@@ -6232,6 +6232,8 @@ class HermesCLI:
             self._console_print(f"  Status bar {state}")
         elif canonical == "verbose":
             self._toggle_verbose()
+        elif canonical == "footer":
+            self._handle_footer_command(cmd_original)
         elif canonical == "yolo":
             self._toggle_yolo()
         elif canonical == "reasoning":
@@ -6859,6 +6861,58 @@ class HermesCLI:
         if self._apply_tui_skin_style():
             print("  Prompt + TUI colors updated.")
 
+    def _handle_footer_command(self, cmd_original: str) -> None:
+        """Toggle or inspect ``display.runtime_footer.enabled`` from the CLI.
+
+        Usage:
+            /footer           → toggle
+            /footer on|off    → explicit
+            /footer status    → show current state
+        """
+        from hermes_cli.config import load_config
+        from hermes_cli.colors import Colors as _Colors
+
+        # Parse arg
+        arg = ""
+        try:
+            parts = (cmd_original or "").strip().split(None, 1)
+            if len(parts) > 1:
+                arg = parts[1].strip().lower()
+        except Exception:
+            arg = ""
+
+        cfg = load_config() or {}
+        footer_cfg = ((cfg.get("display") or {}).get("runtime_footer") or {})
+        current = bool(footer_cfg.get("enabled", False))
+        fields = footer_cfg.get("fields") or ["model", "context_pct", "cwd"]
+
+        if arg in ("status", "?"):
+            state = "ON" if current else "OFF"
+            _cprint(
+                f"  {_Colors.BOLD}Runtime footer:{_Colors.RESET} {state}\n"
+                f"  Fields: {', '.join(fields)}"
+            )
+            return
+
+        if arg in ("on", "enable", "true", "1"):
+            new_state = True
+        elif arg in ("off", "disable", "false", "0"):
+            new_state = False
+        elif arg == "":
+            new_state = not current
+        else:
+            _cprint("  Usage: /footer [on|off|status]")
+            return
+
+        if save_config_value("display.runtime_footer.enabled", new_state):
+            state = (
+                f"{_Colors.GREEN}ON{_Colors.RESET}" if new_state
+                else f"{_Colors.DIM}OFF{_Colors.RESET}"
+            )
+            _cprint(f"  Runtime footer: {state}")
+        else:
+            _cprint("  Failed to save runtime_footer setting to config.yaml")
+
     def _toggle_verbose(self):
         """Cycle tool progress mode: off → new → all → verbose → off."""
         cycle = ["off", "new", "all", "verbose"]