fix(honcho): isolate session routing for multi-user gateway (#1500)

Salvaged from PR #1470 by adavyas.

Core fix: Honcho tool calls in a multi-session gateway could route to
the wrong session because honcho_tools.py relied on process-global
state. Now threads session context through the call chain:
  AIAgent._invoke_tool() → handle_function_call() → registry.dispatch()
  → handler **kw → _resolve_session_context()

Changes:
- Add _resolve_session_context() to prefer per-call context over globals
- Plumb honcho_manager + honcho_session_key through handle_function_call
- Add sync_honcho=False to run_conversation() for synthetic flush turns
- Pass honcho_session_key through gateway memory flush lifecycle
- Harden gateway PID detection when /proc cmdline is unreadable
- Make interrupt test scripts import-safe for pytest-xdist
- Wrap BibTeX examples in Jekyll raw blocks for docs build
- Fix thread-order-dependent assertion in client lifecycle test
- Expand Honcho docs: session isolation, lifecycle, routing internals

Dropped from original PR:
- Indentation change in _create_request_openai_client that would move
  client creation inside the lock (causes unnecessary contention)

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

website/docs/user-guide/features/honcho.md

@@ -247,6 +247,25 @@ Dialectic queries scale reasoning effort with message complexity:
 
 The gateway creates short-lived `AIAgent` instances per request. Honcho managers are owned at the gateway session layer (`_honcho_managers` dict) so they persist across requests within the same session and flush at real session boundaries (reset, resume, expiry, server stop).
 
+#### Session Isolation
+
+Each gateway session (e.g., a Telegram chat, a Discord channel) gets its own Honcho session context. The session key — derived from the platform and chat ID — is threaded through the entire tool dispatch chain so that Honcho tool calls always execute against the correct session, even when multiple users are messaging concurrently.
+
+This means:
+- **`honcho_profile`**, **`honcho_search`**, **`honcho_context`**, and **`honcho_conclude`** all resolve the correct session at call time, not at startup
+- Background memory flushes (triggered by `/reset`, `/resume`, or session expiry) preserve the original session key so they write to the correct Honcho session
+- Synthetic flush turns (where the agent saves memories before context is lost) skip Honcho sync to avoid polluting conversation history with internal bookkeeping
+
+#### Session Lifecycle
+
+| Event | What happens to Honcho |
+|-------|------------------------|
+| New message arrives | Agent inherits the gateway's Honcho manager + session key |
+| `/reset` | Memory flush fires with the old session key, then Honcho manager shuts down |
+| `/resume` | Current session is flushed, then the resumed session's Honcho context loads |
+| Session expiry | Automatic flush + shutdown after the configured idle timeout |
+| Gateway stop | All active Honcho managers are flushed and shut down gracefully |
+
 ## Tools
 
 When Honcho is active, four tools become available. Availability is gated dynamically — they are invisible when Honcho is disabled.