Update enhancement proposal with typed ExternallyDeleted signal design

Replace the (nil, nil) sentinel pattern with a typed ExternallyDeleted
signal on ReconcileStatus. This is a design improvement over the
original proposal: using a dedicated signal prevents ambiguity with
actuator bugs that might also return nil, and restores the safety guard
for unexpected nil returns from GetOSResourceByID.

Author: eshulman2

enhancements/drift-detection.md

@@ -190,10 +190,11 @@ When a resource with `managementPolicy=managed` is deleted from OpenStack but th
 Currently, `GetOrCreateOSResource` returns a terminal error when fetching a resource by `status.id` results in a 404. To support resource recreation, this logic must be updated to:
 
 1. Check if `managementPolicy == managed` and the resource was not imported (no `importID` or `importFilter`)
-2. If both conditions are met, clear `status.id` and proceed to the creation path instead of returning an error
+2. If both conditions are met, return a typed `ExternallyDeleted` signal via `ReconcileStatus` so the caller can clear `status.id` and trigger recreation on the next reconcile
 3. If the resource was imported or is unmanaged, retain the existing terminal error behavior
+4. If `GetOSResourceByID` returns a nil resource with no error (actuator bug), return an explicit error rather than silently misinterpreting it as external deletion
 
-This ensures that managed resources created by ORC are automatically recreated, while imported or unmanaged resources correctly fail with a terminal error when deleted externally.
+This ensures that managed resources created by ORC are automatically recreated, while imported or unmanaged resources correctly fail with a terminal error when deleted externally. The typed signal avoids ambiguity with nil returns from actuator bugs.
 
 **Behavior when drift detection is disabled** (`resyncPeriod: 0`): Periodic resyncs do not occur, so discovery of external deletion depends on other triggers (spec change, controller restart). When discovered, ORC will still recreate managed resources (not a terminal error). The difference is timing of discovery, not the recreation behavior itself.
 
@@ -294,10 +295,11 @@ The following have been implemented:
 **External Deletion Handling**
 - `IsImported()` method added to `APIObjectAdapter` interface (all resource adapters)
 - `GetOrCreateOSResource` branches on management policy and import status when 404 is received:
-  - Managed, non-imported resources → `(nil, nil)` to trigger recreation
+  - Managed, non-imported resources → typed `ExternallyDeleted` signal via `ReconcileStatus`
   - Unmanaged or imported resources → terminal error
+  - Nil resource with no error (actuator bug) → explicit programming error
 - `status.ClearStatusID` clears `status.id` before recreation (using JSON merge patch with explicit `null`)
-- `reconcileNormal` handles the `(nil, nil)` recreation signal from `GetOrCreateOSResource`
+- `reconcileNormal` checks `IsExternallyDeleted()` on the `ReconcileStatus` to trigger recreation
 
 **E2E Tests**
 - `network-resync-period`: verifies `lastSyncTime` is updated after configured period