Fix cross-network block detection and remove false orphan artifacts

- Change OrphanedAt from time.Time to *time.Time so JSON omitempty
  correctly omits zero values (Go serializes zero time.Time as
  "0001-01-01T00:00:00Z" which JS treats as truthy)
- Rewrite reconcileOnce with 4-pass architecture: enrichment, reorg
  detection via GetBlock verification, false-positive un-orphaning,
  and legacy block stamping
- Use inferOtherChain() to stamp cross-network blocks with the correct
  chain identifier (testnet4 reports as "testnet4", not "test")
- Move tailer startup after aggregator's first refresh so blocks are
  always stamped with the current chain
- Add StampChain store method, debug-blocks admin endpoint, and
  comprehensive reconcile tests for cross-network scenarios

api/cmd/kamado-api/main.go

@@ -112,16 +112,10 @@ func main() {
 			}
 		}
 	}
-	go tailer.Run(ctx)
-	go agg.IngestBlockEvents(ctx, tailer.Events)
-	go agg.IngestAttemptEvents(ctx, tailer.Attempts)
-
-	// Wait briefly for the aggregator's first refresh to complete so
-	// the very first /api/snapshot or /api/health hit doesn't see an
-	// all-zeros snapshot and report bitcoin_ok=false during its own
-	// initialization. Cap the wait so a permanently-down bitcoind
-	// can't block startup forever — /healthz is honest about the
-	// degraded state.
+	// Wait for the aggregator's first refresh before starting the log
+	// tailer. This guarantees currentChain is set before any block
+	// events are processed, so blocks are always stamped with the
+	// correct chain — preventing false orphans on network switches.
 	select {
 	case <-agg.Ready():
 		log.Info("first snapshot ready")
@@ -131,6 +125,10 @@ func main() {
 		return
 	}
 
+	go tailer.Run(ctx)
+	go agg.IngestBlockEvents(ctx, tailer.Events)
+	go agg.IngestAttemptEvents(ctx, tailer.Attempts)
+
 	srv := &http.Server{
 		Addr:              cfg.ListenAddr,
 		Handler:           api.Handler(),

api/internal/httpapi/server.go

@@ -37,6 +37,7 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /api/blocks", s.blocks)
 	mux.HandleFunc("GET /api/snapshot", s.snapshot)
 	mux.HandleFunc("GET /api/ws", s.handleWS)
+	mux.HandleFunc("GET /api/admin/debug-blocks", s.debugBlocks)
 	mux.Handle("/", spaHandler(webui.FS()))
 	return mux
 }
@@ -159,3 +160,51 @@ func (s *Server) clients(w http.ResponseWriter, r *http.Request) {
 func (s *Server) blocks(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, s.Agg.Blocks())
 }
+
+// debugBlocks exposes raw block state from both the in-memory snapshot
+// (what the UI sees) and the DB (ground truth) for troubleshooting.
+func (s *Server) debugBlocks(w http.ResponseWriter, r *http.Request) {
+	type row struct {
+		Height     int64   `json:"height"`
+		Hash       string  `json:"hash"`
+		Chain      string  `json:"chain"`
+		OrphanedAt string  `json:"orphaned_at"`
+		FoundAt    string  `json:"found_at"`
+		RewardBTC  float64 `json:"reward_btc"`
+		Source     string  `json:"source"`
+	}
+	fmtBlock := func(b state.BlockRecord) row {
+		orphaned := ""
+		if b.OrphanedAt != nil {
+			orphaned = b.OrphanedAt.Format("2006-01-02T15:04:05Z")
+		}
+		return row{
+			Height:     b.Height,
+			Hash:       b.Hash,
+			Chain:      b.Chain,
+			OrphanedAt: orphaned,
+			FoundAt:    b.FoundAt.Format("2006-01-02T15:04:05Z"),
+			RewardBTC:  b.RewardBT,
+			Source:     b.Source,
+		}
+	}
+
+	// In-memory blocks (what /api/blocks and /api/snapshot serve)
+	memBlocks := s.Agg.Blocks()
+	mem := make([]row, 0, len(memBlocks))
+	for _, b := range memBlocks {
+		mem = append(mem, fmtBlock(b))
+	}
+
+	// DB blocks (ground truth)
+	dbBlocks := s.Agg.BlocksFromStore()
+	db := make([]row, 0, len(dbBlocks))
+	for _, b := range dbBlocks {
+		db = append(db, fmtBlock(b))
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"memory": mem,
+		"db":     db,
+	})
+}

api/internal/state/blocks.go

@@ -16,14 +16,37 @@ import (
 // check finds the recorded hash no longer matches the canonical block
 // at this height (i.e. the network reorged us out).
 type BlockRecord struct {
-	Height     int64     `json:"height"`
-	Hash       string    `json:"hash,omitempty"`
-	RewardBT   float64   `json:"reward_btc,omitempty"`
-	FoundAt    time.Time `json:"found_at"`
-	Source     string    `json:"source"` // "logmon" for now; "zmq" later
-	ShareDiff  float64   `json:"share_diff,omitempty"`
-	OrphanedAt time.Time `json:"orphaned_at,omitempty"`
-	Chain      string    `json:"chain,omitempty"` // "main", "test", "signet"
+	Height     int64      `json:"height"`
+	Hash       string     `json:"hash,omitempty"`
+	RewardBT   float64    `json:"reward_btc,omitempty"`
+	FoundAt    time.Time  `json:"found_at"`
+	Source     string     `json:"source"` // "logmon" for now; "zmq" later
+	ShareDiff  float64    `json:"share_diff,omitempty"`
+	OrphanedAt *time.Time `json:"orphaned_at,omitempty"`
+	Chain      string     `json:"chain,omitempty"` // "main", "test", "signet"
+}
+
+// timePtr returns a pointer to t if non-zero, nil otherwise.
+func timePtr(t time.Time) *time.Time {
+	if t.IsZero() {
+		return nil
+	}
+	return &t
+}
+
+// inferOtherChain returns the most likely chain name for a block that
+// doesn't belong to currentChain. Since the pool only supports mainnet
+// and testnet4, the inference is unambiguous. Note: Bitcoin Core reports
+// testnet4 as "testnet4" (not "test" which is the deprecated testnet3).
+func inferOtherChain(currentChain string) string {
+	switch currentChain {
+	case "main":
+		return "testnet4"
+	case "testnet4":
+		return "main"
+	default:
+		return "other"
+	}
 }
 
 // IngestAttemptEvents counts "Possible/Submitting block solve" log
@@ -171,13 +194,31 @@ func (a *Aggregator) ReconcileBlocks(ctx context.Context) {
 func (a *Aggregator) reconcileOnce(ctx context.Context) {
 	since := time.Now().Add(-reconcileLookback)
 
+	// We need the current chain for both enrichment and reorg detection.
+	// If the first refresh hasn't completed yet, currentChain is "" and
+	// any chain comparison would be meaningless — skip until the next tick.
+	a.mu.RLock()
+	currentChain := ""
+	if a.snap.Chain != nil {
+		currentChain = a.snap.Chain.Chain
+	}
+	a.mu.RUnlock()
+	if currentChain == "" {
+		return
+	}
+
 	// Pass 1: enrichment. Fetch hash + reward for any missing-data rows.
+	// Skip blocks from a different chain — enriching a testnet block
+	// against mainnet RPC would overwrite its hash with the wrong value.
 	missing, err := a.Store.BlocksNeedingEnrichment(since)
 	if err != nil {
 		a.Log.Warn("reconcile: load missing failed", "err", err)
 	}
 	enrichedAny := false
 	for _, b := range missing {
+		if b.Chain != "" && b.Chain != currentChain {
+			continue
+		}
 		lookupCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
 		hash := b.Hash
 		reward := b.RewardBT
@@ -205,29 +246,28 @@ func (a *Aggregator) reconcileOnce(ctx context.Context) {
 		}
 	}
 
-	// Pass 2: reorg detection. For non-orphaned blocks within the
-	// lookback, confirm the canonical hash at that height still
-	// matches our record. Don't bother with rows that are already
-	// orphaned — we won't un-orphan, since the network already
-	// chose another chain.
-	//
-	// Skip blocks whose recorded chain doesn't match the current
-	// bitcoind network — they were mined on a different node config
-	// (e.g. testnet) and cannot be checked against mainnet's tip.
-	// A mismatch here is a false positive, not a real reorg.
-	a.mu.RLock()
-	currentChain := ""
-	if a.snap.Chain != nil {
-		currentChain = a.snap.Chain.Chain
-	}
-	a.mu.RUnlock()
-
 	recent, err := a.Store.Recent(64)
 	if err != nil {
 		a.Log.Warn("reconcile: load recent failed", "err", err)
 		return
 	}
+
+	// Pass 2: reorg detection + cross-network identification.
+	//
+	// For each non-orphaned block within the lookback that has a hash:
+	//   1. If its Chain field already marks it as a different network, skip.
+	//   2. Compare our hash against the canonical hash at that height.
+	//   3. On mismatch, call GetBlock(our_hash) to check if the block
+	//      exists anywhere on the current chain (even if reorged out).
+	//      - If GetBlock succeeds: it's a genuine reorg → mark orphaned.
+	//      - If GetBlock fails ("Block not found"): the block doesn't
+	//        exist on this network at all → it's from a different chain.
+	//        Stamp it and leave it non-orphaned.
+	//
+	// This handles both stamped blocks (Chain="test") and legacy blocks
+	// (Chain="") that were recorded before the chain-stamp feature.
 	orphanedAny := false
+	stampedAny := false
 	now := time.Now()
 	for _, b := range recent {
 		if b.Hash == "" || !b.OrphanedAt.IsZero() {
@@ -236,36 +276,149 @@ func (a *Aggregator) reconcileOnce(ctx context.Context) {
 		if b.FoundAt.Before(since) {
 			continue
 		}
-		// Both chain values must be known before we can compare them.
-		// Legacy rows (Chain=="") fall through so existing installs keep
-		// their reorg detection — there was no network switch before this
-		// feature landed.
-		if b.Chain != "" && currentChain != "" && b.Chain != currentChain {
-			continue
+		if b.Chain != "" && b.Chain != currentChain {
+			continue // already known to be from a different network
 		}
 		lookupCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
 		canonical, herr := a.RPC.GetBlockHash(lookupCtx, b.Height)
 		cancel()
 		if herr != nil {
-			// Most likely cause: our bitcoind doesn't have this
-			// height yet (index lag). Try again next sweep — don't
-			// orphan on a transient RPC error.
-			continue
+			continue // RPC transient error — retry next sweep
 		}
-		if canonical != b.Hash {
-			if err := a.Store.MarkOrphaned(b.Height, now); err != nil {
-				a.Log.Warn("reconcile: mark orphaned failed", "height", b.Height, "err", err)
+		if canonical == b.Hash {
+			continue // matches the canonical chain — all good
+		}
+		// Hash mismatch. Determine whether it's a real reorg or a
+		// cross-network block by checking if our hash exists on this chain.
+		// After a real reorg, bitcoind still has the stale block in its
+		// store; a cross-network hash won't exist at all.
+		lookupCtx2, cancel2 := context.WithTimeout(ctx, 3*time.Second)
+		_, berr := a.RPC.GetBlock(lookupCtx2, b.Hash)
+		cancel2()
+		if berr != nil {
+			// Block not found on this network → cross-network block.
+			// Stamp its chain so future sweeps skip it immediately.
+			otherChain := b.Chain
+			if otherChain == "" {
+				otherChain = inferOtherChain(currentChain)
+			}
+			if err := a.Store.StampChain(b.Height, otherChain); err != nil {
+				a.Log.Warn("reconcile: stamp cross-network block failed", "height", b.Height, "err", err)
 				continue
 			}
-			a.Log.Warn("reconcile: block orphaned by reorg",
-				"height", b.Height, "ours", b.Hash, "canonical", canonical)
-			orphanedAny = true
+			a.Log.Info("reconcile: block belongs to a different network, not a reorg",
+				"height", b.Height, "hash", b.Hash, "block_chain", otherChain, "current_chain", currentChain)
+			stampedAny = true
+			continue
+		}
+		// Block exists on this network but isn't canonical → genuine reorg.
+		if err := a.Store.MarkOrphaned(b.Height, now); err != nil {
+			a.Log.Warn("reconcile: mark orphaned failed", "height", b.Height, "err", err)
+			continue
+		}
+		a.Log.Warn("reconcile: block orphaned by reorg",
+			"height", b.Height, "ours", b.Hash, "canonical", canonical)
+		orphanedAny = true
+	}
+
+	// Pass 3: un-orphan blocks that were previously false-positived.
+	// This covers two cases:
+	//   a) Blocks with Chain != currentChain that got orphaned before this
+	//      fix was deployed — un-orphan them now.
+	//   b) Same-chain blocks whose hash now matches the canonical chain
+	//      (e.g. the "reorg" reverted before we checked again).
+	fixedAny := false
+	for _, b := range recent {
+		if b.OrphanedAt.IsZero() || b.Hash == "" {
+			continue
+		}
+		if b.FoundAt.Before(since) {
+			continue
+		}
+		if b.Chain != "" && b.Chain != currentChain {
+			// Cross-network orphan from before the fix — un-orphan.
+			if err := a.Store.UnmarkOrphaned(b.Height); err != nil {
+				a.Log.Warn("reconcile: unmark cross-network orphan failed", "height", b.Height, "err", err)
+				continue
+			}
+			a.Log.Info("reconcile: cleared false orphan (different network)",
+				"height", b.Height, "block_chain", b.Chain, "current_chain", currentChain)
+			fixedAny = true
+			continue
+		}
+		// For same-chain or legacy blocks: verify via RPC.
+		lookupCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
+		_, berr := a.RPC.GetBlock(lookupCtx, b.Hash)
+		cancel()
+		if berr != nil {
+			// Block doesn't exist on this chain — cross-network.
+			otherChain := b.Chain
+			if otherChain == "" || otherChain == currentChain {
+				otherChain = inferOtherChain(currentChain)
+			}
+			if err := a.Store.UnmarkOrphanedStampChain(b.Height, otherChain); err != nil {
+				a.Log.Warn("reconcile: unmark+stamp cross-network orphan failed", "height", b.Height, "err", err)
+				continue
+			}
+			a.Log.Info("reconcile: cleared false orphan (block not on this network)",
+				"height", b.Height, "hash", b.Hash, "stamped_chain", otherChain)
+			fixedAny = true
+			continue
+		}
+		// Block exists on this chain — check if it's canonical again.
+		lookupCtx2, cancel2 := context.WithTimeout(ctx, 3*time.Second)
+		canonical, herr := a.RPC.GetBlockHash(lookupCtx2, b.Height)
+		cancel2()
+		if herr != nil {
+			continue
+		}
+		if canonical == b.Hash {
+			if err := a.Store.UnmarkOrphaned(b.Height); err != nil {
+				a.Log.Warn("reconcile: unmark reverted-reorg failed", "height", b.Height, "err", err)
+				continue
+			}
+			a.Log.Info("reconcile: cleared orphan — hash matches canonical again",
+				"height", b.Height, "hash", b.Hash)
+			fixedAny = true
 		}
 	}
 
-	if enrichedAny || orphanedAny {
-		// Refresh the in-memory ring so the snapshot picks up the
-		// changes immediately rather than waiting for the next poll.
+	// Pass 4: stamp chain on legacy/mis-stamped blocks that have a hash.
+	// Handles Chain="" (never stamped), "other" (old fallback), and "test"
+	// (wrong identifier — testnet4 reports as "testnet4", not "test").
+	// Uses GetBlock(hash) to determine if the block belongs to the current
+	// network or a different one. No lookback restriction — this is a
+	// one-time migration for pre-existing rows.
+	for _, b := range recent {
+		if (b.Chain != "" && b.Chain != "other" && b.Chain != "test") || b.Hash == "" {
+			continue // already properly stamped or no hash to check
+		}
+		lookupCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
+		_, berr := a.RPC.GetBlock(lookupCtx, b.Hash)
+		cancel()
+		if berr != nil {
+			// Block not found on this network — infer the other chain.
+			inferredChain := inferOtherChain(currentChain)
+			if err := a.Store.StampChain(b.Height, inferredChain); err != nil {
+				a.Log.Warn("reconcile: stamp legacy block failed", "height", b.Height, "err", err)
+				continue
+			}
+			a.Log.Info("reconcile: stamped legacy block as other-network",
+				"height", b.Height, "hash", b.Hash, "inferred_chain", inferredChain)
+			stampedAny = true
+		} else {
+			// Block exists on this network
+			if err := a.Store.StampChain(b.Height, currentChain); err != nil {
+				a.Log.Warn("reconcile: stamp legacy block failed", "height", b.Height, "err", err)
+				continue
+			}
+			a.Log.Info("reconcile: stamped legacy block as current chain",
+				"height", b.Height, "chain", currentChain)
+			stampedAny = true
+		}
+	}
+
+	if enrichedAny || orphanedAny || stampedAny || fixedAny {
 		a.loadPersistedBlocks()
 		a.mu.RLock()
 		snap := a.snap
@@ -320,7 +473,7 @@ func (a *Aggregator) loadPersistedBlocks() {
 			FoundAt:    r.FoundAt,
 			Source:     r.Source,
 			ShareDiff:  r.ShareDiff,
-			OrphanedAt: r.OrphanedAt,
+			OrphanedAt: timePtr(r.OrphanedAt),
 			Chain:      r.Chain,
 		})
 	}
@@ -354,3 +507,31 @@ func (a *Aggregator) Blocks() []BlockRecord {
 	copy(out, a.blocks)
 	return out
 }
+
+// BlocksFromStore reads blocks directly from the DB (bypassing in-memory
+// cache) for debugging discrepancies between memory and store.
+func (a *Aggregator) BlocksFromStore() []BlockRecord {
+	if a.Store == nil {
+		return nil
+	}
+	rows, err := a.Store.Recent(maxBlockHistory)
+	if err != nil {
+		return nil
+	}
+	out := make([]BlockRecord, 0, len(rows))
+	for i := len(rows) - 1; i >= 0; i-- {
+		r := rows[i]
+		out = append(out, BlockRecord{
+			Height:     r.Height,
+			Hash:       r.Hash,
+			RewardBT:   r.RewardBT,
+			FoundAt:    r.FoundAt,
+			Source:     r.Source,
+			ShareDiff:  r.ShareDiff,
+			OrphanedAt: timePtr(r.OrphanedAt),
+			Chain:      r.Chain,
+		})
+	}
+	return out
+}
+

api/internal/state/blocks_test.go

@@ -108,10 +108,15 @@ func TestReconcileOnce_ChainFilter_NoFalseOrphan(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	// Mock RPC returns a DIFFERENT hash for height 100 — mainnet canonical.
+	// Mock RPC: getblockhash returns a different mainnet hash; getblock
+	// for our testnet hash returns "Block not found" — it doesn't exist
+	// on mainnet at all, confirming it's cross-network not a reorg.
 	rpc := mockRPC(t, func(method string) (any, *rpcErrResp) {
-		if method == "getblockhash" {
+		switch method {
+		case "getblockhash":
 			return "mainnet_hash_bbb", nil
+		case "getblock":
+			return nil, &rpcErrResp{Code: -5, Message: "Block not found"}
 		}
 		return nil, nil
 	})
@@ -150,9 +155,17 @@ func TestReconcileOnce_GenuineReorg(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// getblockhash returns a different canonical hash (reorg happened).
+	// getblock for our hash SUCCEEDS — the block still exists in bitcoind's
+	// block store after a reorg, it's just no longer on the active chain.
+	// This distinguishes a real reorg from a cross-network block.
 	rpc := mockRPC(t, func(method string) (any, *rpcErrResp) {
-		if method == "getblockhash" {
-			return "canonical_bbbb", nil // different — reorg happened
+		switch method {
+		case "getblockhash":
+			return "canonical_bbbb", nil
+		case "getblock":
+			// Block exists (reorged but still in store)
+			return map[string]any{"hash": "our_hash_aaaa", "height": 200, "confirmations": -1}, nil
 		}
 		return nil, nil
 	})
@@ -215,7 +228,7 @@ func TestReconcileOnce_RPCError_NoOrphan(t *testing.T) {
 	}
 }
 
-// TestReconcileOnce_LegacyBlock_StillChecked verifies that a legacy block
+// TestReconcileOnce_LegacyBlock_GenuineReorg verifies that a legacy block
 // (Chain == "") is still checked for reorgs on the current chain, preserving
 // backward compatibility for installs that existed before chain was tracked.
 func TestReconcileOnce_LegacyBlock_StillChecked(t *testing.T) {
@@ -230,10 +243,15 @@ func TestReconcileOnce_LegacyBlock_StillChecked(t *testing.T) {
 		Chain:    "", // legacy — no chain recorded
 	})
 
-	// Mainnet canonical hash differs: should orphan even though Chain is empty.
+	// Canonical hash differs AND getblock succeeds (block exists on this
+	// chain but was reorged out). Should still orphan legacy blocks.
 	rpc := mockRPC(t, func(method string) (any, *rpcErrResp) {
-		if method == "getblockhash" {
+		switch method {
+		case "getblockhash":
 			return "different_canonical", nil
+		case "getblock":
+			// Block exists in this chain's store — genuine reorg
+			return map[string]any{"hash": "legacy_hash", "height": 400, "confirmations": -1}, nil
 		}
 		return nil, nil
 	})
@@ -251,6 +269,51 @@ func TestReconcileOnce_LegacyBlock_StillChecked(t *testing.T) {
 	}
 }
 
+// TestReconcileOnce_LegacyBlock_CrossNetwork verifies that a legacy block
+// (Chain == "") whose hash doesn't exist on the current chain is identified
+// as cross-network and stamped rather than orphaned.
+func TestReconcileOnce_LegacyBlock_CrossNetwork(t *testing.T) {
+	st := openTempStore(t)
+
+	st.InsertBlock(store.Block{
+		Height:   401,
+		Hash:     "other_network_hash",
+		RewardBT: 50,
+		FoundAt:  time.Now(),
+		Source:   "test",
+		Chain:    "", // legacy — no chain recorded
+	})
+
+	// Canonical hash differs AND getblock fails (block doesn't exist on
+	// this network at all). Should NOT orphan — should stamp as "other".
+	rpc := mockRPC(t, func(method string) (any, *rpcErrResp) {
+		switch method {
+		case "getblockhash":
+			return "mainnet_canonical", nil
+		case "getblock":
+			return nil, &rpcErrResp{Code: -5, Message: "Block not found"}
+		}
+		return nil, nil
+	})
+
+	agg := newAgg(st, rpc)
+	setChain(agg, "main")
+
+	agg.reconcileOnce(context.Background())
+
+	blocks, _ := st.Recent(10)
+	for _, b := range blocks {
+		if b.Height == 401 {
+			if !b.OrphanedAt.IsZero() {
+				t.Error("cross-network legacy block was falsely orphaned")
+			}
+			if b.Chain != "testnet4" {
+				t.Errorf("expected chain stamped as 'testnet4' (inferred from current=main), got %q", b.Chain)
+			}
+		}
+	}
+}
+
 // ---- IngestBlockEvents tests ----
 
 // TestIngestBlockEvents_NewBlock verifies that a fresh block event is

api/internal/store/blocks.go

@@ -287,3 +287,41 @@ func (s *BlockStore) MarkOrphaned(height int64, at time.Time) error {
 	)
 	return err
 }
+
+// UnmarkOrphaned clears the orphaned_at stamp set by MarkOrphaned.
+// Used to correct false positives caused by a network switch: a block
+// found on testnet is not "orphaned" when the node switches to mainnet —
+// it simply belongs to a different chain and must not be compared against
+// mainnet's canonical history.
+func (s *BlockStore) UnmarkOrphaned(height int64) error {
+	_, err := s.db.Exec(
+		`UPDATE blocks SET orphaned_at = 0 WHERE height = ?`,
+		height,
+	)
+	return err
+}
+
+// UnmarkOrphanedStampChain clears orphaned_at and simultaneously sets the
+// chain field. Used for legacy rows (chain == "") that were falsely orphaned
+// during a network switch: by stamping a non-mainnet chain value we prevent
+// the reconcile reorg-detection pass from re-checking the block against the
+// current chain's canonical hashes.
+func (s *BlockStore) UnmarkOrphanedStampChain(height int64, chain string) error {
+	_, err := s.db.Exec(
+		`UPDATE blocks SET orphaned_at = 0, chain = ? WHERE height = ?`,
+		chain, height,
+	)
+	return err
+}
+
+// StampChain sets the chain field on a block without touching orphaned_at.
+// Used when the reconcile loop determines a block belongs to a different
+// network — the block is not orphaned (a reorg), it just doesn't belong
+// to the current chain.
+func (s *BlockStore) StampChain(height int64, chain string) error {
+	_, err := s.db.Exec(
+		`UPDATE blocks SET chain = ? WHERE height = ?`,
+		chain, height,
+	)
+	return err
+}