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

agent/title_generator.py

@@ -0,0 +1,125 @@
+"""Auto-generate short session titles from the first user/assistant exchange.
+
+Runs asynchronously after the first response is delivered so it never
+adds latency to the user-facing reply.
+"""
+
+import logging
+import threading
+from typing import Optional
+
+from agent.auxiliary_client import call_llm
+
+logger = logging.getLogger(__name__)
+
+_TITLE_PROMPT = (
+    "Generate a short, descriptive title (3-7 words) for a conversation that starts with the "
+    "following exchange. The title should capture the main topic or intent. "
+    "Return ONLY the title text, nothing else. No quotes, no punctuation at the end, no prefixes."
+)
+
+
+def generate_title(user_message: str, assistant_response: str, timeout: float = 15.0) -> Optional[str]:
+    """Generate a session title from the first exchange.
+
+    Uses the auxiliary LLM client (cheapest/fastest available model).
+    Returns the title string or None on failure.
+    """
+    # Truncate long messages to keep the request small
+    user_snippet = user_message[:500] if user_message else ""
+    assistant_snippet = assistant_response[:500] if assistant_response else ""
+
+    messages = [
+        {"role": "system", "content": _TITLE_PROMPT},
+        {"role": "user", "content": f"User: {user_snippet}\n\nAssistant: {assistant_snippet}"},
+    ]
+
+    try:
+        response = call_llm(
+            task="compression",  # reuse compression task config (cheap/fast model)
+            messages=messages,
+            max_tokens=30,
+            temperature=0.3,
+            timeout=timeout,
+        )
+        title = (response.choices[0].message.content or "").strip()
+        # Clean up: remove quotes, trailing punctuation, prefixes like "Title: "
+        title = title.strip('"\'')
+        if title.lower().startswith("title:"):
+            title = title[6:].strip()
+        # Enforce reasonable length
+        if len(title) > 80:
+            title = title[:77] + "..."
+        return title if title else None
+    except Exception as e:
+        logger.debug("Title generation failed: %s", e)
+        return None
+
+
+def auto_title_session(
+    session_db,
+    session_id: str,
+    user_message: str,
+    assistant_response: str,
+) -> None:
+    """Generate and set a session title if one doesn't already exist.
+
+    Called in a background thread after the first exchange completes.
+    Silently skips if:
+    - session_db is None
+    - session already has a title (user-set or previously auto-generated)
+    - title generation fails
+    """
+    if not session_db or not session_id:
+        return
+
+    # Check if title already exists (user may have set one via /title before first response)
+    try:
+        existing = session_db.get_session_title(session_id)
+        if existing:
+            return
+    except Exception:
+        return
+
+    title = generate_title(user_message, assistant_response)
+    if not title:
+        return
+
+    try:
+        session_db.set_session_title(session_id, title)
+        logger.debug("Auto-generated session title: %s", title)
+    except Exception as e:
+        logger.debug("Failed to set auto-generated title: %s", e)
+
+
+def maybe_auto_title(
+    session_db,
+    session_id: str,
+    user_message: str,
+    assistant_response: str,
+    conversation_history: list,
+) -> None:
+    """Fire-and-forget title generation after the first exchange.
+
+    Only generates a title when:
+    - This appears to be the first user→assistant exchange
+    - No title is already set
+    """
+    if not session_db or not session_id or not user_message or not assistant_response:
+        return
+
+    # Count user messages in history to detect first exchange.
+    # conversation_history includes the exchange that just happened,
+    # so for a first exchange we expect exactly 1 user message
+    # (or 2 counting system). Be generous: generate on first 2 exchanges.
+    user_msg_count = sum(1 for m in (conversation_history or []) if m.get("role") == "user")
+    if user_msg_count > 2:
+        return
+
+    thread = threading.Thread(
+        target=auto_title_session,
+        args=(session_db, session_id, user_message, assistant_response),
+        daemon=True,
+        name="auto-title",
+    )
+    thread.start()