diff --git a/src/activity_core/activities.py b/src/activity_core/activities.py
index c85ddba..9de8d41 100644
--- a/src/activity_core/activities.py
+++ b/src/activity_core/activities.py
@@ -12,6 +12,7 @@ activities that need DB access.
 from __future__ import annotations
 
 import uuid
+from datetime import datetime, timezone
 
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
@@ -20,6 +21,7 @@ from temporalio.exceptions import ApplicationError
 
 from activity_core.db import make_engine
 from activity_core.orm import ActivityDefinition as ActivityDefinitionRow
+from activity_core.orm import ActivityRun
 
 
 _session_factory: async_sessionmaker[AsyncSession] | None = None
@@ -116,8 +118,35 @@ async def resolve_context(context_sources: list[dict]) -> dict:
 
 @activity.defn
 async def log_run(run_payload: dict) -> str:
-    """Persist an ActivityRun record and return its run_id.
+    """Persist an ActivityRun record to Postgres and return its run_id.
 
-    Implemented in T17.
+    Expected keys in run_payload:
+        activity_id       (str UUID)
+        scheduled_for     (ISO-8601 str or None)
+        context_snapshot  (dict)
+        tasks_spawned     (int)
+        version_used      (int)
+
+    Returns:
+        run_id as a str UUID.
     """
-    raise NotImplementedError("T17")
+    Session = _get_session_factory()
+
+    scheduled_for: datetime | None = None
+    if run_payload.get("scheduled_for"):
+        scheduled_for = datetime.fromisoformat(run_payload["scheduled_for"])
+
+    row = ActivityRun(
+        activity_id=uuid.UUID(run_payload["activity_id"]),
+        scheduled_for=scheduled_for,
+        fired_at=datetime.now(tz=timezone.utc),
+        context_snapshot=run_payload["context_snapshot"],
+        tasks_spawned=run_payload["tasks_spawned"],
+        version_used=run_payload["version_used"],
+    )
+
+    async with Session() as session:
+        async with session.begin():
+            session.add(row)
+
+    return str(row.run_id)
diff --git a/workplans/custodian-WP-0001-temporal-backbone.md b/workplans/custodian-WP-0001-temporal-backbone.md
index a883dfe..c3ee57f 100644
--- a/workplans/custodian-WP-0001-temporal-backbone.md
+++ b/workplans/custodian-WP-0001-temporal-backbone.md
@@ -72,7 +72,7 @@ tasks:
     state_hub_task_id: b7decbb6-ad2b-4fa5-8efc-05a7eb435d76
   - id: T17
     title: Implement log_run activity
-    status: todo
+    status: done
     state_hub_task_id: e019cb5a-adf0-4a5d-9410-c41810128190
   - id: T18
     title: Implement RunActivityWorkflow