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>

tests/gateway/test_status.py

@@ -26,6 +26,22 @@ class TestGatewayPidState:
         assert status.get_running_pid() is None
         assert not pid_path.exists()
 
+    def test_get_running_pid_accepts_gateway_metadata_when_cmdline_unavailable(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        pid_path = tmp_path / "gateway.pid"
+        pid_path.write_text(json.dumps({
+            "pid": os.getpid(),
+            "kind": "hermes-gateway",
+            "argv": ["python", "-m", "hermes_cli.main", "gateway"],
+            "start_time": 123,
+        }))
+
+        monkeypatch.setattr(status.os, "kill", lambda pid, sig: None)
+        monkeypatch.setattr(status, "_get_process_start_time", lambda pid: 123)
+        monkeypatch.setattr(status, "_read_process_cmdline", lambda pid: None)
+
+        assert status.get_running_pid() == os.getpid()
+
 
 class TestGatewayRuntimeStatus:
     def test_write_runtime_status_records_platform_failure(self, tmp_path, monkeypatch):