fix(gc): skip deleted miner actors in StorageGCMark instead of failing

When a miner actor no longer exists on-chain (e.g. removed from config
after deletion), StorageGCMark would fail with 'actor not found' and
enter a permanent retry loop, blocking all storage GC.

Handle the actor-not-found case gracefully in both Stage 1 (sector
liveness check) and Stage 3 (snap sector-key cleanup):

- Stage 1: Skip loading miner state for deleted actors. Their sectors
  remain in the toRemove set since there are no on-chain precommits,
  live, or unproven sectors to subtract.
- Stage 3: Skip finality-tipset actor lookups for deleted miners.
  Snap sector-key cleanup is irrelevant for non-existent miners.

Only the specific 'actor not found' error triggers this path. Transient
RPC errors (timeouts, connection issues) still fail the task as before,
preventing accidental GC of sectors for healthy miners during network
disruptions.

Fixes a scenario where removing a calibration/test miner from config
causes StorageGCMark to fail 100% of runs indefinitely.

Author: Reiers

tasks/gc/storage_gc_mark.go

@@ -3,6 +3,7 @@ package gc
 import (
 	"context"
 	"fmt"
+	"strings"
 	"time"
 
 	cbor "github.com/ipfs/go-ipld-cbor"
@@ -122,6 +123,13 @@ func (s *StorageGCMark) Do(taskID harmonytask.TaskID, stillOwned func() bool) (d
 
 				mact, err := s.api.StateGetActor(ctx, maddr, types.EmptyTSK)
 				if err != nil {
+					if isActorNotFoundErr(err) {
+						// Miner actor no longer exists on-chain. Sector files for this
+						// miner are orphaned — skip loading state so that all its sectors
+						// remain in toRemove (no precommit/live/unproven subtraction).
+						log.Warnw("miner actor not found on-chain, treating sectors as orphaned for GC", "miner", maddr)
+						continue
+					}
 					return false, xerrors.Errorf("get miner actor %s: %w", maddr, err)
 				}
 
@@ -383,6 +391,12 @@ func (s *StorageGCMark) Do(taskID harmonytask.TaskID, stillOwned func() bool) (d
 
 		mact, err := s.api.StateGetActor(ctx, maddr, finalityTipset.Key())
 		if err != nil {
+			if isActorNotFoundErr(err) {
+				// Miner actor no longer exists on-chain at finality height.
+				// Skip — snap sector key cleanup is irrelevant for a deleted miner.
+				log.Warnw("miner actor not found at finality height, skipping snap-key GC", "miner", maddr)
+				continue
+			}
 			return false, xerrors.Errorf("get miner actor %s at finality: %w", maddr, err)
 		}
 
@@ -501,3 +515,15 @@ func (s *StorageGCMark) Adder(taskFunc harmonytask.AddTaskFunc) {
 
 var _ harmonytask.TaskInterface = &StorageGCMark{}
 var _ = harmonytask.Reg(&StorageGCMark{})
+
+// isActorNotFoundErr checks whether the error indicates that a miner actor
+// does not exist on-chain. Because Curio talks to Lotus via JSON-RPC, the
+// typed types.ErrActorNotFound / api.ErrActorNotFound may not survive the
+// round-trip. Fall back to a string check consistent with existing callers
+// in sptool (see cmd/sptool/toolbox_deal_client.go).
+func isActorNotFoundErr(err error) bool {
+	if err == nil {
+		return false
+	}
+	return strings.Contains(err.Error(), "actor not found")
+}