feat: auto-generate session titles after first exchange

After the first user→assistant exchange, Hermes now generates a short
descriptive session title via the auxiliary LLM (compression task config).
Title generation runs in a background thread so it never delays the
user-facing response.

Key behaviors:
- Fires only on the first 1-2 exchanges (checks user message count)
- Skips if a title already exists (user-set titles are never overwritten)
- Uses call_llm with compression task config (cheapest/fastest model)
- Truncates long messages to keep the title generation request small
- Cleans up LLM output: strips quotes, 'Title:' prefixes, enforces 80 char max
- Works in both CLI and gateway (Telegram/Discord/etc.)

Also updates /title (no args) to show the session ID alongside the title
in both CLI and gateway.

Implements #1426

tests/agent/test_title_generator.py

@@ -0,0 +1,160 @@
+"""Tests for agent.title_generator — auto-generated session titles."""
+
+import threading
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from agent.title_generator import (
+    generate_title,
+    auto_title_session,
+    maybe_auto_title,
+)
+
+
+class TestGenerateTitle:
+    """Unit tests for generate_title()."""
+
+    def test_returns_title_on_success(self):
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock()]
+        mock_response.choices[0].message.content = "Debugging Python Import Errors"
+
+        with patch("agent.title_generator.call_llm", return_value=mock_response):
+            title = generate_title("help me fix this import", "Sure, let me check...")
+            assert title == "Debugging Python Import Errors"
+
+    def test_strips_quotes(self):
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock()]
+        mock_response.choices[0].message.content = '"Setting Up Docker Environment"'
+
+        with patch("agent.title_generator.call_llm", return_value=mock_response):
+            title = generate_title("how do I set up docker", "First install...")
+            assert title == "Setting Up Docker Environment"
+
+    def test_strips_title_prefix(self):
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock()]
+        mock_response.choices[0].message.content = "Title: Kubernetes Pod Debugging"
+
+        with patch("agent.title_generator.call_llm", return_value=mock_response):
+            title = generate_title("my pod keeps crashing", "Let me look...")
+            assert title == "Kubernetes Pod Debugging"
+
+    def test_truncates_long_titles(self):
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock()]
+        mock_response.choices[0].message.content = "A" * 100
+
+        with patch("agent.title_generator.call_llm", return_value=mock_response):
+            title = generate_title("question", "answer")
+            assert len(title) == 80
+            assert title.endswith("...")
+
+    def test_returns_none_on_empty_response(self):
+        mock_response = MagicMock()
+        mock_response.choices = [MagicMock()]
+        mock_response.choices[0].message.content = ""
+
+        with patch("agent.title_generator.call_llm", return_value=mock_response):
+            assert generate_title("question", "answer") is None
+
+    def test_returns_none_on_exception(self):
+        with patch("agent.title_generator.call_llm", side_effect=RuntimeError("no provider")):
+            assert generate_title("question", "answer") is None
+
+    def test_truncates_long_messages(self):
+        """Long user/assistant messages should be truncated in the LLM request."""
+        captured_kwargs = {}
+
+        def mock_call_llm(**kwargs):
+            captured_kwargs.update(kwargs)
+            resp = MagicMock()
+            resp.choices = [MagicMock()]
+            resp.choices[0].message.content = "Short Title"
+            return resp
+
+        with patch("agent.title_generator.call_llm", side_effect=mock_call_llm):
+            generate_title("x" * 1000, "y" * 1000)
+
+        # The user content in the messages should be truncated
+        user_content = captured_kwargs["messages"][1]["content"]
+        assert len(user_content) < 1100  # 500 + 500 + formatting
+
+
+class TestAutoTitleSession:
+    """Tests for auto_title_session() — the sync worker function."""
+
+    def test_skips_if_no_session_db(self):
+        auto_title_session(None, "sess-1", "hi", "hello")  # should not crash
+
+    def test_skips_if_title_exists(self):
+        db = MagicMock()
+        db.get_session_title.return_value = "Existing Title"
+
+        with patch("agent.title_generator.generate_title") as gen:
+            auto_title_session(db, "sess-1", "hi", "hello")
+            gen.assert_not_called()
+
+    def test_generates_and_sets_title(self):
+        db = MagicMock()
+        db.get_session_title.return_value = None
+
+        with patch("agent.title_generator.generate_title", return_value="New Title"):
+            auto_title_session(db, "sess-1", "hi", "hello")
+            db.set_session_title.assert_called_once_with("sess-1", "New Title")
+
+    def test_skips_if_generation_fails(self):
+        db = MagicMock()
+        db.get_session_title.return_value = None
+
+        with patch("agent.title_generator.generate_title", return_value=None):
+            auto_title_session(db, "sess-1", "hi", "hello")
+            db.set_session_title.assert_not_called()
+
+
+class TestMaybeAutoTitle:
+    """Tests for maybe_auto_title() — the fire-and-forget entry point."""
+
+    def test_skips_if_not_first_exchange(self):
+        """Should not fire for conversations with more than 2 user messages."""
+        db = MagicMock()
+        history = [
+            {"role": "user", "content": "first"},
+            {"role": "assistant", "content": "response 1"},
+            {"role": "user", "content": "second"},
+            {"role": "assistant", "content": "response 2"},
+            {"role": "user", "content": "third"},
+            {"role": "assistant", "content": "response 3"},
+        ]
+
+        with patch("agent.title_generator.auto_title_session") as mock_auto:
+            maybe_auto_title(db, "sess-1", "third", "response 3", history)
+            # Wait briefly for any thread to start
+            import time
+            time.sleep(0.1)
+            mock_auto.assert_not_called()
+
+    def test_fires_on_first_exchange(self):
+        """Should fire a background thread for the first exchange."""
+        db = MagicMock()
+        db.get_session_title.return_value = None
+        history = [
+            {"role": "user", "content": "hello"},
+            {"role": "assistant", "content": "hi there"},
+        ]
+
+        with patch("agent.title_generator.auto_title_session") as mock_auto:
+            maybe_auto_title(db, "sess-1", "hello", "hi there", history)
+            # Wait for the daemon thread to complete
+            import time
+            time.sleep(0.3)
+            mock_auto.assert_called_once_with(db, "sess-1", "hello", "hi there")
+
+    def test_skips_if_no_response(self):
+        db = MagicMock()
+        maybe_auto_title(db, "sess-1", "hello", "", [])  # empty response
+
+    def test_skips_if_no_session_db(self):
+        maybe_auto_title(None, "sess-1", "hello", "response", [])  # no db