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fix(mcp): avoid replaying historical events on startup (#13414)

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EventBridge initialized each session's last_seen timestamp to 0.0, so
the first poll after 'hermes mcp serve' starts treated every saved
user/assistant message in state.db as a fresh events_poll event.

The fix establishes a per-session timestamp baseline on startup via
_establish_baseline(), recording the latest existing message timestamp
without emitting events. Only messages written after the baseline are
delivered on subsequent polls.

Also hoists _ts_float to module-level (needed by _establish_baseline)
and adds ImportError fallbacks for hermes_constants imports so the
bridge works in environments where the module isn't on the path.

Salvage of #13414 by @afurm, re-applied by @HeLLGURD in #41239.

Co-authored-by: afurm <afurm@users.noreply.github.com>
This commit is contained in:
HeLLGURD
2026-08-01 11:17:03 +05:30
committed by kshitij
parent 57b1eb8c4d
commit d109138ef5
2 changed files with 482 additions and 26 deletions
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mcp_serve.py
+81 -26
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@@ -62,9 +62,11 @@ except ImportError:
def _get_sessions_dir() -> Path:
"""Return the sessions directory using HERMES_HOME."""
from hermes_constants import get_hermes_home
return get_hermes_home() / "sessions"
try:
from hermes_constants import get_hermes_home
return get_hermes_home() / "sessions"
except ImportError:
return Path(os.environ.get("HERMES_HOME", Path.home() / ".hermes")) / "sessions"
def _get_session_db():
@@ -192,9 +194,13 @@ def _load_sessions_index_from_json() -> dict:
def _load_channel_directory() -> dict:
"""Load the cached channel directory for available targets."""
from hermes_constants import get_hermes_home
directory_file = get_hermes_home() / "channel_directory.json"
try:
from hermes_constants import get_hermes_home
directory_file = get_hermes_home() / "channel_directory.json"
except ImportError:
directory_file = Path(
os.environ.get("HERMES_HOME", Path.home() / ".hermes")
) / "channel_directory.json"
if not directory_file.exists():
return {}
@@ -292,6 +298,21 @@ class QueueEvent:
data: dict = field(default_factory=dict)
def _ts_float(ts) -> float:
"""Normalize a message timestamp (epoch int/float or ISO string) to float."""
if isinstance(ts, (int, float)):
return float(ts)
if isinstance(ts, str) and ts:
try:
return float(ts)
except ValueError:
try:
return datetime.fromisoformat(ts).timestamp()
except Exception:
return 0.0
return 0.0
class EventBridge:
"""Background poller that watches SessionDB for new messages and
maintains an in-memory event queue with waiter support.
@@ -318,6 +339,13 @@ class EventBridge:
"""Start the background polling thread."""
if self._running:
return
# Snapshot existing history BEFORE the poll loop starts so pre-existing
# messages are not replayed as new events on startup (#13414). Sessions
# that first appear afterwards are absent from the baseline and default
# to last_seen=0.0 in _poll_once, so new-conversation delivery is
# preserved. Unit tests that drive _poll_once directly bypass start()
# and still observe first-poll delivery.
self._establish_baseline()
self._running = True
self._thread = threading.Thread(target=self._poll_loop, daemon=True)
self._thread.start()
@@ -419,6 +447,46 @@ class EventBridge:
self._queue.pop(0)
self._new_event.set()
def _establish_baseline(self) -> None:
"""Record the latest per-session message timestamp and the current
state.db mtime WITHOUT emitting events, so startup does not replay
history (#13414).
Only sessions that already exist at startup are baselined; a session
that first appears afterwards is absent here and defaults to
last_seen=0.0 in _poll_once, so a brand-new conversation's first
message is still delivered on its state.db-change tick.
"""
db = _get_session_db()
if not db:
return
try:
from hermes_constants import get_hermes_home
db_file = get_hermes_home() / "state.db"
except ImportError:
db_file = Path(os.environ.get("HERMES_HOME", Path.home() / ".hermes")) / "state.db"
try:
self._state_db_mtime = db_file.stat().st_mtime if db_file.exists() else 0.0
except OSError:
self._state_db_mtime = 0.0
try:
self._cached_sessions_index = _load_sessions_index()
except Exception:
self._cached_sessions_index = {}
for session_key, entry in self._cached_sessions_index.items():
session_id = entry.get("session_id", "")
if not session_id:
continue
try:
messages = db.get_messages(session_id)
except Exception:
continue
all_ts = [_ts_float(m.get("timestamp", 0)) for m in (messages or ())]
if all_ts:
latest = max(all_ts)
if latest > 0.0:
self._last_poll_timestamps[session_key] = latest
def _poll_loop(self):
"""Background loop: poll SessionDB for new messages."""
db = _get_session_db()
@@ -444,9 +512,11 @@ class EventBridge:
eliminating the old dual-file (sessions.json + state.db) race that
could drop brand-new conversations (#8925).
"""
from hermes_constants import get_hermes_home
db_file = get_hermes_home() / "state.db"
try:
from hermes_constants import get_hermes_home
db_file = get_hermes_home() / "state.db"
except ImportError:
db_file = Path(os.environ.get("HERMES_HOME", Path.home() / ".hermes")) / "state.db"
try:
db_mtime = db_file.stat().st_mtime if db_file.exists() else 0.0
@@ -478,23 +548,8 @@ class EventBridge:
if not messages:
continue
# Normalize timestamps to float for comparison
def _ts_float(ts) -> float:
if isinstance(ts, (int, float)):
return float(ts)
if isinstance(ts, str) and ts:
try:
return float(ts)
except ValueError:
# ISO string — parse to epoch
try:
from datetime import datetime
return datetime.fromisoformat(ts).timestamp()
except Exception:
return 0.0
return 0.0
# Find messages newer than our last seen timestamp
# Find messages newer than our last seen timestamp (see the
# module-level _ts_float helper for timestamp normalization).
new_messages = []
for msg in messages:
ts = _ts_float(msg.get("timestamp", 0))