fix(charts): validate same-time comparison publications

Prompt-only projection rules allowed historical samples to be appended to the current axis. Enforce typed comparison semantics at presentation and report publication, preserving historical read contracts and returning actionable validation errors.

app/services/operational_tasks.py

@@ -74,6 +74,7 @@ from app.services.content_digest import digest
 from app.services.operational_presentation import resolve_overlay
 from app.services.operational_recovery import accept_completion, track_work_order
 from app.services.operational_scada_coverage import require_complete_scada_evidence
+from app.services.time_comparison_chart import validate_time_comparison_chart
 
 
 LEASE_DURATION = timedelta(seconds=60)
@@ -837,6 +838,11 @@ class OperationalTaskService:
                     "Only a running run accepts Agent artifacts", status=409)
             now = self._now()
             self._require_active_run_lease(active_run, now)
+            if command.report:
+                for item in command.report.ui_blocks:
+                    for element in item.block.spec.elements.values():
+                        if element.type == "Chart":
+                            validate_time_comparison_chart(element.props)
             if command.report and (
                 command.report.stage == "final" or command.report.outcome == "insufficient_data"
             ):
@@ -1095,6 +1101,7 @@ class OperationalTaskService:
             self._require_active_run_lease(run, now)
             payload = _json(command.command)
             if command.command.action == "open_chart":
+                validate_time_comparison_chart(payload["chart"])
                 known = {item["evidence_id"] for item in await self.repo.list_evidence(str(task_id))}
                 self._require_evidence_refs(command.command.evidence_refs, known)
             elif command.command.action == "set_overlay":