fix: tolerate null DuckDB message ids in fingerprints

Legacy or manually repaired DuckDB mirrors can contain message rows where id is NULL even though normal pushes write the mirrored local primary key. The new message-id fingerprint should treat that as a mismatch to repair, not as a scan error that aborts incremental push.

Scan message ids as nullable and add regression coverage that corrupts a mirrored id to NULL, then verifies the next incremental push rewrites the session and restores the local id.

Author: cpcloud

internal/duckdb/push_fingerprint.go

@@ -209,7 +209,7 @@ func duckStoredMessageFingerprint(
 	var token strings.Builder
 	for rows.Next() {
 		var ordinal, contentLength, contextTokens, outputTokens int
-		var id int64
+		var id sql.NullInt64
 		var role, content, thinkingText, model, tokenUsage string
 		var claudeMsgID, claudeReqID string
 		var srcType, srcSubtype, srcUUID, srcParentUUID string
@@ -240,7 +240,7 @@ func duckStoredMessageFingerprint(
 		}
 		fp.Count++
 		fp.Sum += int64(contentLength)
-		fmt.Fprintf(&messageIDs, "%d|%d;", ordinal, id)
+		fmt.Fprintf(&messageIDs, "%d|%t|%d;", ordinal, id.Valid, id.Int64)
 		if isSystem {
 			if systemOrdinals.Len() > 0 {
 				systemOrdinals.WriteByte(',')

internal/duckdb/sync_fastpath_test.go

@@ -186,6 +186,38 @@ func TestSyncIncrementalMessageIDChangeFallsBackToRewrite(t *testing.T) {
 	), "curation refresh must point pins at mirrored messages")
 }
 
+func TestSyncIncrementalNullMirrorMessageIDFallsBackToRewrite(t *testing.T) {
+	ctx := context.Background()
+	local := newLocalDB(t)
+	fixture := seedDuckDBSyncFixture(t, local)
+	syncer := newInMemoryTestSync(t, local, SyncOptions{})
+
+	first, err := syncer.Push(ctx, true, nil)
+	require.NoError(t, err)
+	require.Equal(t, 2, first.SessionsPushed)
+	localMessages, err := local.GetAllMessages(ctx, fixture.betaID)
+	require.NoError(t, err)
+	require.Len(t, localMessages, 1)
+	_, err = syncer.DB().ExecContext(ctx,
+		`UPDATE messages SET id = NULL WHERE session_id = ? AND ordinal = ?`,
+		fixture.betaID, 0,
+	)
+	require.NoError(t, err)
+
+	time.Sleep(time.Millisecond)
+	renameSessionOnly(t, local, fixture.betaID, "beta null id repair")
+	second, err := syncer.Push(ctx, false, nil)
+	require.NoError(t, err)
+
+	assert.Equal(t, 1, second.SessionsPushed)
+	assert.Equal(t, 1, second.MessagesPushed)
+	assert.Equal(t,
+		localMessages[0].ID,
+		duckMessageID(t, syncer.DB(), fixture.betaID, 0),
+		"NULL mirrored message ids must force a repair rewrite",
+	)
+}
+
 func TestSyncIncrementalToolResultEventChangeUpdatesMirror(t *testing.T) {
 	ctx := context.Background()
 	local := newLocalDB(t)