fix(ops_run): unique triggering_event_id per cron fire

Cron schedules always passed trigger_key="scheduled", so ops_run
idempotency collapsed every weekday into one key. After the first fire,
create_ops_run was a silent no-op, the claim loop starved, and dual-clock
host timers produced empty FI briefs.

Map scheduled fires to run_id (or scheduled:{iso}) via
emit_triggering_event_id; log duplicate skips; document the contract.

src/activity_core/workflows.py

@@ -30,6 +30,7 @@ with workflow.unsafe.imports_passed_through():
         persist_task_instance,
         resolve_context,
     )
+    from activity_core.ops_run_queue import emit_triggering_event_id
     from activity_core.schedule_manager import SCHEDULED_TRIGGER_KEY
 
 # T32: Custom search attributes for Temporal visibility (must be registered in Temporal first).
@@ -197,12 +198,21 @@ class RunActivityWorkflow:
 
         # ── 6. Emit tasks (may fail independently of run audit) ───────────────
         if task_spec_dicts:
+            # Cron schedules pass trigger_key="scheduled" for *every* fire.
+            # ops_run idempotency is {def}:{source}:{triggering_event_id}, so
+            # a bare "scheduled" key collides after the first day and silently
+            # skips create (claim loop starves; dual-clock timers paper over it).
+            # run_id is uuid5(workflow_id) for schedules and is unique per fire
+            # while stable on Temporal redelivery of the same fire.
+            emit_trigger_id = emit_triggering_event_id(
+                trigger_key, run_id, scheduled_for=scheduled_for
+            )
             await workflow.execute_activity(
                 emit_tasks,
                 {
                     "task_specs": task_spec_dicts,
                     "activity_id": activity_id,
-                    "triggering_event_id": trigger_key,
+                    "triggering_event_id": emit_trigger_id,
                     "run_id": run_id,
                 },
                 start_to_close_timeout=_ACTIVITY_TIMEOUT,