feat(gateway): surface session config on /new, /reset, and auto-reset

When a new session starts in the gateway (via /new, /reset, or
auto-reset), send the user a summary of the detected configuration:

  ✨ Session reset! Starting fresh.

  ◆ Model: qwen3.5:27b-q4_K_M
  ◆ Provider: custom
  ◆ Context: 8K tokens (config)
  ◆ Endpoint: http://localhost:11434/v1

This makes misconfigured context length immediately visible — a user
running a local 8K model that falls to the 128K default will see:

  ◆ Context: 128K tokens (default — set model.context_length in config to override)

Instead of silently getting no compression and degrading responses.

- _format_session_info() resolves model, provider, context length,
  and endpoint from config + runtime, matching the hygiene code's
  resolution chain
- Local/custom endpoints shown; cloud endpoints hidden (not useful)
- Context source annotated: config, detected, or default with hint
- Appended to /new and /reset responses, and auto-reset notifications
- 9 tests covering all formatting paths and failure resilience

Addresses the user-facing side of #2708 — instead of trying to fix
every edge case in context detection, surface the values so users
can immediately see when something is wrong.

gateway/run.py

@@ -1982,6 +1982,12 @@ class GatewayRunner:
                             f"Use /resume to browse and restore a previous session.\n"
                             f"Adjust reset timing in config.yaml under session_reset."
                         )
+                        try:
+                            session_info = self._format_session_info()
+                            if session_info:
+                                notice = f"{notice}\n\n{session_info}"
+                        except Exception:
+                            pass
                         await adapter.send(
                             source.chat_id, notice,
                             metadata=getattr(event, 'metadata', None),
@@ -2749,6 +2755,85 @@ class GatewayRunner:
             # Clear session env
             self._clear_session_env()
     
+    def _format_session_info(self) -> str:
+        """Resolve current model config and return a formatted info block.
+
+        Surfaces model, provider, context length, and endpoint so gateway
+        users can immediately see if context detection went wrong (e.g.
+        local models falling to the 128K default).
+        """
+        from agent.model_metadata import get_model_context_length, DEFAULT_FALLBACK_CONTEXT
+
+        model = _resolve_gateway_model()
+        config_context_length = None
+        provider = None
+        base_url = None
+        api_key = None
+
+        try:
+            cfg_path = _hermes_home / "config.yaml"
+            if cfg_path.exists():
+                import yaml as _info_yaml
+                with open(cfg_path, encoding="utf-8") as f:
+                    data = _info_yaml.safe_load(f) or {}
+                model_cfg = data.get("model", {})
+                if isinstance(model_cfg, dict):
+                    raw_ctx = model_cfg.get("context_length")
+                    if raw_ctx is not None:
+                        try:
+                            config_context_length = int(raw_ctx)
+                        except (TypeError, ValueError):
+                            pass
+                    provider = model_cfg.get("provider") or None
+                    base_url = model_cfg.get("base_url") or None
+        except Exception:
+            pass
+
+        # Resolve runtime credentials for probing
+        try:
+            runtime = _resolve_runtime_agent_kwargs()
+            provider = provider or runtime.get("provider")
+            base_url = base_url or runtime.get("base_url")
+            api_key = runtime.get("api_key")
+        except Exception:
+            pass
+
+        context_length = get_model_context_length(
+            model,
+            base_url=base_url or "",
+            api_key=api_key or "",
+            config_context_length=config_context_length,
+            provider=provider or "",
+        )
+
+        # Format context source hint
+        if config_context_length is not None:
+            ctx_source = "config"
+        elif context_length == DEFAULT_FALLBACK_CONTEXT:
+            ctx_source = "default — set model.context_length in config to override"
+        else:
+            ctx_source = "detected"
+
+        # Format context length for display
+        if context_length >= 1_000_000:
+            ctx_display = f"{context_length / 1_000_000:.1f}M"
+        elif context_length >= 1_000:
+            ctx_display = f"{context_length // 1_000}K"
+        else:
+            ctx_display = str(context_length)
+
+        lines = [
+            f"◆ Model: `{model}`",
+            f"◆ Provider: {provider or 'openrouter'}",
+            f"◆ Context: {ctx_display} tokens ({ctx_source})",
+        ]
+
+        # Show endpoint for local/custom setups
+        if base_url and ("localhost" in base_url or "127.0.0.1" in base_url or "0.0.0.0" in base_url):
+            lines.append(f"◆ Endpoint: {base_url}")
+
+        return "\n".join(lines)
+
     async def _handle_reset_command(self, event: MessageEvent) -> str:
         """Handle /new or /reset command."""
         source = event.source
@@ -2789,12 +2874,22 @@ class GatewayRunner:
             "session_key": session_key,
         })
         
+        # Resolve session config info to surface to the user
+        try:
+            session_info = self._format_session_info()
+        except Exception:
+            session_info = ""
+
         if new_entry:
-            return "✨ Session reset! I've started fresh with no memory of our previous conversation."
+            header = "✨ Session reset! Starting fresh."
         else:
             # No existing session, just create one
             self.session_store.get_or_create_session(source, force_new=True)
-            return "✨ New session started!"
+            header = "✨ New session started!"
+
+        if session_info:
+            return f"{header}\n\n{session_info}"
+        return header
     
     async def _handle_status_command(self, event: MessageEvent) -> str:
         """Handle /status command."""

tests/gateway/test_session_info.py

@@ -0,0 +1,110 @@
+"""Tests for GatewayRunner._format_session_info — session config surfacing."""
+
+import pytest
+from unittest.mock import patch, MagicMock
+from pathlib import Path
+
+from gateway.run import GatewayRunner
+
+
+@pytest.fixture()
+def runner():
+    """Create a bare GatewayRunner without __init__."""
+    return GatewayRunner.__new__(GatewayRunner)
+
+
+def _patch_info(tmp_path, config_yaml, model, runtime):
+    """Return a context-manager stack that patches _format_session_info deps."""
+    cfg_path = tmp_path / "config.yaml"
+    if config_yaml is not None:
+        cfg_path.write_text(config_yaml)
+    return (
+        patch("gateway.run._hermes_home", tmp_path),
+        patch("gateway.run._resolve_gateway_model", return_value=model),
+        patch("gateway.run._resolve_runtime_agent_kwargs", return_value=runtime),
+    )
+
+
+class TestFormatSessionInfo:
+
+    def test_includes_model_name(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: anthropic/claude-opus-4.6\n  provider: openrouter\n",
+                                  "anthropic/claude-opus-4.6",
+                                  {"provider": "openrouter", "base_url": "https://openrouter.ai/api/v1", "api_key": "k"})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "claude-opus-4.6" in info
+
+    def test_includes_provider(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: test-model\n  provider: openrouter\n",
+                                  "test-model",
+                                  {"provider": "openrouter", "base_url": "", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "openrouter" in info
+
+    def test_config_context_length(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: test-model\n  context_length: 32768\n",
+                                  "test-model",
+                                  {"provider": "custom", "base_url": "", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "32K" in info
+        assert "config" in info
+
+    def test_default_fallback_hint(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: unknown-model-xyz\n",
+                                  "unknown-model-xyz",
+                                  {"provider": "", "base_url": "", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "128K" in info
+        assert "model.context_length" in info
+
+    def test_local_endpoint_shown(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(
+            tmp_path,
+            "model:\n  default: qwen3:8b\n  provider: custom\n  base_url: http://localhost:11434/v1\n  context_length: 8192\n",
+            "qwen3:8b",
+            {"provider": "custom", "base_url": "http://localhost:11434/v1", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "localhost:11434" in info
+        assert "8K" in info
+
+    def test_cloud_endpoint_hidden(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: test-model\n  provider: openrouter\n",
+                                  "test-model",
+                                  {"provider": "openrouter", "base_url": "https://openrouter.ai/api/v1", "api_key": "k"})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "Endpoint" not in info
+
+    def test_million_context_format(self, runner, tmp_path):
+        p1, p2, p3 = _patch_info(tmp_path, "model:\n  default: test-model\n  context_length: 1000000\n",
+                                  "test-model",
+                                  {"provider": "", "base_url": "", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "1.0M" in info
+
+    def test_missing_config(self, runner, tmp_path):
+        """No config.yaml should not crash."""
+        p1, p2, p3 = _patch_info(tmp_path, None,  # don't create config
+                                  "anthropic/claude-sonnet-4.6",
+                                  {"provider": "openrouter", "base_url": "", "api_key": ""})
+        with p1, p2, p3:
+            info = runner._format_session_info()
+        assert "Model" in info
+        assert "Context" in info
+
+    def test_runtime_resolution_failure_doesnt_crash(self, runner, tmp_path):
+        """If runtime resolution raises, should still produce output."""
+        cfg_path = tmp_path / "config.yaml"
+        cfg_path.write_text("model:\n  default: test-model\n  context_length: 4096\n")
+        with patch("gateway.run._hermes_home", tmp_path), \
+             patch("gateway.run._resolve_gateway_model", return_value="test-model"), \
+             patch("gateway.run._resolve_runtime_agent_kwargs", side_effect=RuntimeError("no creds")):
+            info = runner._format_session_info()
+        assert "4K" in info
+        assert "config" in info