fix(storage): make span ingest idempotent for DLQ replay

internal/storage/factory.go

@@ -238,6 +238,15 @@ func AutoMigrateModelsWithOptions(db *gorm.DB, driver string, opts MigrateOption
 		logsPartitioned = true
 	}
 
+	// Dedupe spans BEFORE AutoMigrate adds the composite uniqueIndex
+	// idx_spans_tenant_trace_span on (tenant_id, trace_id, span_id).
+	// Pre-RAN-65 deployments may have duplicates from DLQ replays; the
+	// unique index would fail to create against violating rows. No-op on
+	// fresh databases or when the unique index already exists.
+	if err := dedupeSpansForUniqueIndex(db, driver); err != nil {
+		log.Printf("⚠️  span dedupe before unique index failed: %v", err)
+	}
+
 	migrateModels := []any{&Trace{}, &Span{}, &MetricBucket{}}
 	if !logsPartitioned {
 		migrateModels = append(migrateModels, &Log{})

internal/storage/migrate_spans.go

@@ -0,0 +1,102 @@
+package storage
+
+import (
+	"fmt"
+	"log"
+	"strings"
+
+	"gorm.io/gorm"
+)
+
+// dedupeSpansForUniqueIndex collapses any pre-existing duplicate spans on
+// (tenant_id, trace_id, span_id) before AutoMigrate adds the composite
+// uniqueIndex. Without this, CREATE UNIQUE INDEX would fail on databases
+// that accumulated duplicates from earlier DLQ replays (or any pre-RAN-65
+// non-idempotent ingest path), aborting startup.
+//
+// Strategy across drivers: keep the lowest primary-key row per
+// (tenant_id, trace_id, span_id), delete the rest. Idempotent — a fresh
+// database (or one that never collected duplicates) is a no-op.
+//
+// Must run BEFORE db.AutoMigrate(...) in AutoMigrateModels; once the
+// unique constraint is in place, the dedupe is unnecessary because new
+// inserts collapse via OnConflict.DoNothing.
+func dedupeSpansForUniqueIndex(db *gorm.DB, driver string) error {
+	if db == nil {
+		return nil
+	}
+	driver = strings.ToLower(driver)
+
+	// Skip if the spans table doesn't exist yet — fresh databases have
+	// nothing to dedupe and the upcoming AutoMigrate will create the
+	// table with the uniqueIndex already in place.
+	if !db.Migrator().HasTable("spans") {
+		return nil
+	}
+
+	// Skip if the unique index already exists (idempotent re-runs).
+	if db.Migrator().HasIndex("spans", "idx_spans_tenant_trace_span") {
+		return nil
+	}
+
+	var deleted int64
+	switch driver {
+	case "sqlite", "":
+		// SQLite supports DELETE with subquery on same table.
+		res := db.Exec(`DELETE FROM spans WHERE id NOT IN (
+			SELECT MIN(id) FROM spans GROUP BY tenant_id, trace_id, span_id
+		)`)
+		if res.Error != nil {
+			return fmt.Errorf("dedupe spans (sqlite): %w", res.Error)
+		}
+		deleted = res.RowsAffected
+
+	case "postgres", "postgresql":
+		// USING self-join keeps the lowest id per (tenant, trace, span).
+		res := db.Exec(`DELETE FROM spans a USING spans b
+			WHERE a.id > b.id
+			  AND a.tenant_id = b.tenant_id
+			  AND a.trace_id = b.trace_id
+			  AND a.span_id = b.span_id`)
+		if res.Error != nil {
+			return fmt.Errorf("dedupe spans (postgres): %w", res.Error)
+		}
+		deleted = res.RowsAffected
+
+	case "mysql":
+		// MySQL forbids referencing the target table directly inside a
+		// DELETE subquery; route through a temp table to keep the
+		// "minimum id wins" semantics portable.
+		if err := db.Exec(`CREATE TEMPORARY TABLE _spans_dedupe_keep AS
+			SELECT MIN(id) AS id FROM spans GROUP BY tenant_id, trace_id, span_id`).Error; err != nil {
+			return fmt.Errorf("dedupe spans (mysql temp table): %w", err)
+		}
+		defer db.Exec("DROP TEMPORARY TABLE IF EXISTS _spans_dedupe_keep")
+		res := db.Exec(`DELETE FROM spans
+			WHERE id NOT IN (SELECT id FROM _spans_dedupe_keep)`)
+		if res.Error != nil {
+			return fmt.Errorf("dedupe spans (mysql): %w", res.Error)
+		}
+		deleted = res.RowsAffected
+
+	case "sqlserver", "mssql":
+		// T-SQL: ROW_NUMBER() over the dedupe key, then delete duplicates.
+		res := db.Exec(`WITH dups AS (
+			SELECT id, ROW_NUMBER() OVER (
+				PARTITION BY tenant_id, trace_id, span_id ORDER BY id
+			) AS rn FROM spans
+		) DELETE FROM spans WHERE id IN (SELECT id FROM dups WHERE rn > 1)`)
+		if res.Error != nil {
+			return fmt.Errorf("dedupe spans (mssql): %w", res.Error)
+		}
+		deleted = res.RowsAffected
+
+	default:
+		return nil
+	}
+
+	if deleted > 0 {
+		log.Printf("🧹 Deduplicated %d duplicate span row(s) before adding uniqueIndex idx_spans_tenant_trace_span", deleted)
+	}
+	return nil
+}

internal/storage/models.go

@@ -110,11 +110,19 @@ type Trace struct {
 }
 
 // Span represents a single operation within a trace.
+//
+// Idempotency: the composite uniqueIndex idx_spans_tenant_trace_span on
+// (tenant_id, trace_id, span_id) ensures a span is written at most once
+// per tenant. DLQ replay (or any duplicate ingest) collapses cleanly via
+// OnConflict.DoNothing in BatchCreateAll/BatchCreateSpans rather than
+// double-counting in downstream metrics or GraphRAG. The composite covers
+// the legacy idx_spans_tenant_trace as a left-prefix; the legacy index
+// is retained for query-plan stability across upgrades.
 type Span struct {
 	ID             uint           `gorm:"primaryKey" json:"id"`
-	TenantID       string         `gorm:"size:64;default:'default';not null;index:idx_spans_tenant_trace,priority:1;index:idx_spans_tenant_service_start,priority:1" json:"tenant_id"`
-	TraceID        string         `gorm:"size:32;not null;index:idx_spans_tenant_trace,priority:2" json:"trace_id"`
-	SpanID         string         `gorm:"size:16;not null" json:"span_id"`
+	TenantID       string         `gorm:"size:64;default:'default';not null;index:idx_spans_tenant_trace,priority:1;index:idx_spans_tenant_service_start,priority:1;uniqueIndex:idx_spans_tenant_trace_span,priority:1" json:"tenant_id"`
+	TraceID        string         `gorm:"size:32;not null;index:idx_spans_tenant_trace,priority:2;uniqueIndex:idx_spans_tenant_trace_span,priority:2" json:"trace_id"`
+	SpanID         string         `gorm:"size:16;not null;uniqueIndex:idx_spans_tenant_trace_span,priority:3" json:"span_id"`
 	ParentSpanID   string         `gorm:"size:16" json:"parent_span_id"`
 	OperationName  string         `gorm:"size:255;index" json:"operation_name"`
 	StartTime      time.Time      `gorm:"index:idx_spans_tenant_service_start,priority:3" json:"start_time"`