fix: clarify unavailable legacy blocker resolution

central/app/control_api.py

@@ -6,7 +6,7 @@ from fastapi import APIRouter, Depends, HTTPException, Request
 from sqlalchemy import select
 
 from .audit import record_audit
-from .blocker_resolution import resolve_blocker_with_context
+from .blocker_resolution import BlockerResolutionUnavailable, resolve_blocker_with_context
 from .control_plane import dashboard_summary, installation_view, list_blockers, list_installations, list_jobs, list_panel_events
 from .human_auth import require_csrf, require_human
 from .models import Agent, AgentSnapshot, BlockedProduct, Installation, Job, Tenant
@@ -119,6 +119,8 @@ def router(session_factory):
             entry_payload = {key: payload.get(key) for key in ("scope", "scope_key", "key", "value", "reason")}
             try:
                 return resolve_blocker_with_context(session, blocker_id, admin, entry_payload, request_ip=request.client.host if request.client else None)
+            except BlockerResolutionUnavailable as error:
+                raise HTTPException(409, str(error)) from error
             except LookupError as error:
                 raise HTTPException(404, str(error)) from error
             except ValueError as error: