Problem

Background review notifications were surfacing old successful tool results from the conversation history as if they had just been performed by the review agent.

For example, after a user created a cron job in an earlier turn, a later unrelated background review would repeat:

💾 Cron job '<reminder name>' created. · User profile updated

...even though the review agent never touched cron — it only updated the profile.

Reported in #14944. Related code path also noted in #9055 and #9696.

Root Cause

_spawn_background_review passes conversation_history=messages_snapshot to the review agent, which populates _session_messages with the full prior history (including old role=tool messages). The post-run scan then iterated over all of _session_messages — treating historical tool results as new review actions.

# Before: scans entire _session_messages including snapshot history
for msg in getattr(review_agent, "_session_messages", []):
    ...

Fix

Record the snapshot length before run_conversation(), then slice to only the messages the review agent actually appended:

snapshot_len = len(messages_snapshot)
all_msgs = getattr(review_agent, "_session_messages", [])
new_msgs = all_msgs[snapshot_len:]  # only messages added by the review agent

for msg in new_msgs:
    ...

This is a minimal, zero-risk change — it only affects which messages are summarised in the notification, not the review agent's behaviour or memory writes.

Tests

Added tests/agent/test_bg_review_stale_tool_results.py with 7 unit tests:

All 7 pass ✅

Closes #14944