diff --git a/hindsight-api-slim/hindsight_api/engine/consolidation/consolidator.py b/hindsight-api-slim/hindsight_api/engine/consolidation/consolidator.py
index 4f331149e1..2dcce2ab39 100644
--- a/hindsight-api-slim/hindsight_api/engine/consolidation/consolidator.py
+++ b/hindsight-api-slim/hindsight_api/engine/consolidation/consolidator.py
@@ -28,6 +28,7 @@
 from itertools import combinations
 from typing import TYPE_CHECKING, Any, Literal
 
+import asyncpg
 from pydantic import BaseModel, field_validator
 
 from ...config import get_config
@@ -1775,15 +1776,22 @@ async def _append_observation_history(
     history from growing without bound.
     """
     obs_uuid = uuid.UUID(observation_id)
-    await conn.execute(
-        f"""
+    try:
+        await conn.execute(
+            f"""
         INSERT INTO {fq_table("observation_history")} (observation_id, bank_id, content, changed_at)
         VALUES ($1, $2, $3::jsonb, now())
         """,
-        obs_uuid,
-        bank_id,
-        json.dumps(asdict(snapshot)),
-    )
+            obs_uuid,
+            bank_id,
+            json.dumps(asdict(snapshot)),
+        )
+    except asyncpg.exceptions.ForeignKeyViolationError:
+        logger.warning(
+            f"FK violation writing observation_history for {observation_id}: "
+            "observation was removed before history could be written (race with parallel consolidation). Skipping."
+        )
+        return
     if max_entries and max_entries > 0:
         await conn.execute(
             f"""
diff --git a/hindsight-api-slim/tests/test_observation_history_fk_race.py b/hindsight-api-slim/tests/test_observation_history_fk_race.py
new file mode 100644
index 0000000000..00dcde2731
--- /dev/null
+++ b/hindsight-api-slim/tests/test_observation_history_fk_race.py
@@ -0,0 +1,48 @@
+"""Regression: observation_history write for a since-deleted observation is skipped.
+
+Under parallel (or same-batch delete-then-update) consolidation, one write path
+can remove an observation from ``memory_units`` before another writes its
+``observation_history`` snapshot. The INSERT then trips
+``observation_history_observation_id_fkey``. Because consolidation runs in
+autocommit (no enclosing transaction), catching the FK violation and skipping
+the best-effort history row is safe — the connection stays usable and the
+current observation state remains the source of truth.
+
+Regression for #2597 / #2506: before the fix this raised
+``asyncpg.ForeignKeyViolationError`` and failed the whole consolidation task.
+"""
+
+import uuid
+
+import pytest
+
+from hindsight_api.engine.consolidation.consolidator import (
+    _append_observation_history,
+    _ObservationHistorySnapshot,
+)
+from hindsight_api.engine.db_utils import acquire_with_retry
+
+
+@pytest.mark.asyncio
+async def test_append_history_for_missing_observation_is_skipped(memory, request_context):
+    """A history write targeting an absent observation is skipped, not fatal."""
+    bank_id = f"test-obs-history-fk-{uuid.uuid4().hex[:8]}"
+    await memory.get_bank_profile(bank_id, request_context=request_context)
+
+    snapshot = _ObservationHistorySnapshot(
+        previous_text="old",
+        previous_tags=[],
+        previous_occurred_start=None,
+        previous_occurred_end=None,
+        previous_mentioned_at=None,
+        new_source_memory_ids=[],
+    )
+    # Never inserted into memory_units, so the FK target is absent.
+    missing_observation_id = str(uuid.uuid4())
+
+    pool = await memory._get_pool()
+    async with acquire_with_retry(pool) as conn:
+        # Pre-fix this raised asyncpg.ForeignKeyViolationError; the fix skips it.
+        await _append_observation_history(conn, bank_id, missing_observation_id, snapshot, max_entries=10)
+        # Autocommit: the failed INSERT did not poison the connection.
+        assert await conn.fetchval("SELECT 1") == 1