diff --git a/backend/internal/store/store_test.go b/backend/internal/store/store_test.go
index 74a01dd..33e1fcd 100644
--- a/backend/internal/store/store_test.go
+++ b/backend/internal/store/store_test.go
@@ -2,7 +2,10 @@ package store
 
 import (
 	"context"
+	"database/sql"
+	"io/fs"
 	"path/filepath"
+	"sort"
 	"strings"
 	"testing"
 )
@@ -291,6 +294,167 @@ func TestForeignKeyEnforcementPostMigration(t *testing.T) {
 	}
 }
 
+// TestRebuildMigrationsPreserveForeignKeyReferences proves the specific
+// property none of the other migration tests cover: every other test opens
+// a fresh DB via store.Open, which runs migrations 0001-0025 in one
+// uninterrupted pass over an empty database, so migrations 0023/0024/0025's
+// table-rebuild (create-new/copy/drop-old/rename-into-place) never has any
+// real pre-existing rows to carry across. A real single-tenant deployment
+// upgrading to this schema version has months of synced activities and
+// kind_assignments rows referencing real workout_kinds rows by foreign key
+// (per this repo's CLAUDE.md: one profile, real Garmin history, a review
+// queue with manual overrides already recorded). This test manually applies
+// migrations up through 0022, inserts rows simulating that pre-existing
+// install, then applies 0023/0024/0025 and verifies the FK-referencing row
+// still resolves correctly -- and that FK enforcement is genuinely back on
+// afterward -- rather than just checking that migrations apply to an empty
+// DB without erroring.
+func TestRebuildMigrationsPreserveForeignKeyReferences(t *testing.T) {
+	ctx := context.Background()
+	path := filepath.Join(t.TempDir(), "geniusrun_rebuild_test.db")
+
+	// Deliberately not store.Open: that always applies every migration in
+	// one uninterrupted pass with no way to stop partway through. The sqlite
+	// driver itself is already registered via db.go's blank import.
+	sqlDB, err := sql.Open("sqlite", path+"?_pragma=foreign_keys(1)")
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	defer sqlDB.Close()
+
+	if _, err := sqlDB.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (
+		filename TEXT PRIMARY KEY,
+		applied_at TEXT NOT NULL DEFAULT (datetime('now'))
+	)`); err != nil {
+		t.Fatalf("create schema_migrations table: %v", err)
+	}
+
+	rebuildMigrations := map[string]bool{
+		"0023_profile_user_scoped.sql":       true,
+		"0024_workout_kinds_user_scoped.sql": true,
+		"0025_sync_state_user_scoped.sql":    true,
+	}
+
+	// Mirrors db.go's migrate() method: FK toggle in autocommit mode around
+	// the transaction, only for the three table-rebuild migrations.
+	applyMigration := func(name string) {
+		t.Helper()
+		content, err := migrationsFS.ReadFile("migrations/" + name)
+		if err != nil {
+			t.Fatalf("read migration %s: %v", name, err)
+		}
+
+		needsFKToggle := rebuildMigrations[name]
+		if needsFKToggle {
+			if _, err := sqlDB.ExecContext(ctx, `PRAGMA foreign_keys = OFF`); err != nil {
+				t.Fatalf("disable foreign keys before migration %s: %v", name, err)
+			}
+		}
+
+		tx, err := sqlDB.BeginTx(ctx, nil)
+		if err != nil {
+			t.Fatalf("begin migration tx for %s: %v", name, err)
+		}
+		if _, err := tx.ExecContext(ctx, string(content)); err != nil {
+			tx.Rollback()
+			t.Fatalf("apply migration %s: %v", name, err)
+		}
+		if _, err := tx.ExecContext(ctx, `INSERT INTO schema_migrations (filename) VALUES (?)`, name); err != nil {
+			tx.Rollback()
+			t.Fatalf("record migration %s: %v", name, err)
+		}
+		if err := tx.Commit(); err != nil {
+			t.Fatalf("commit migration %s: %v", name, err)
+		}
+
+		if needsFKToggle {
+			if _, err := sqlDB.ExecContext(ctx, `PRAGMA foreign_keys = ON`); err != nil {
+				t.Fatalf("enable foreign keys after migration %s: %v", name, err)
+			}
+		}
+	}
+
+	entries, err := fs.Glob(migrationsFS, "migrations/*.sql")
+	if err != nil {
+		t.Fatalf("glob migrations: %v", err)
+	}
+	sort.Strings(entries)
+
+	// Apply every migration up to (but not including) the three rebuilds.
+	for _, entry := range entries {
+		name := entry[len("migrations/"):]
+		if rebuildMigrations[name] {
+			continue
+		}
+		applyMigration(name)
+	}
+
+	// Simulate a real pre-existing single-tenant install at this point in
+	// schema history: a workout kind, a synced activity, and a
+	// kind_assignment referencing both by foreign key.
+	res, err := sqlDB.ExecContext(ctx, `INSERT INTO workout_kinds (name, rule_json) VALUES ('Pre-Existing Custom Kind', '{}')`)
+	if err != nil {
+		t.Fatalf("insert pre-existing workout_kinds row: %v", err)
+	}
+	kindID, err := res.LastInsertId()
+	if err != nil {
+		t.Fatalf("workout_kinds LastInsertId: %v", err)
+	}
+
+	res, err = sqlDB.ExecContext(ctx, `
+		INSERT INTO activities (garmin_activity_id, start_time_utc, duration_seconds, distance_meters, raw_json)
+		VALUES (123456789, '2026-01-01 06:00:00', 1800, 5000, '{}')`)
+	if err != nil {
+		t.Fatalf("insert pre-existing activities row: %v", err)
+	}
+	activityID, err := res.LastInsertId()
+	if err != nil {
+		t.Fatalf("activities LastInsertId: %v", err)
+	}
+
+	res, err = sqlDB.ExecContext(ctx, `
+		INSERT INTO kind_assignments (activity_id, workout_kind_id, assignment_source, status)
+		VALUES (?, ?, 'rule_engine', 'assigned')`, activityID, kindID)
+	if err != nil {
+		t.Fatalf("insert pre-existing kind_assignments row: %v", err)
+	}
+	assignmentID, err := res.LastInsertId()
+	if err != nil {
+		t.Fatalf("kind_assignments LastInsertId: %v", err)
+	}
+
+	// Now apply the three rebuild migrations that drop/recreate profile,
+	// workout_kinds, and sync_state.
+	for _, name := range []string{
+		"0023_profile_user_scoped.sql",
+		"0024_workout_kinds_user_scoped.sql",
+		"0025_sync_state_user_scoped.sql",
+	} {
+		applyMigration(name)
+	}
+
+	// The pre-existing kind_assignment row must still resolve to the same
+	// workout_kind, by the same name, across the drop/recreate/rename.
+	var resolvedName string
+	if err := sqlDB.QueryRowContext(ctx, `
+		SELECT wk.name FROM kind_assignments ka
+		JOIN workout_kinds wk ON wk.id = ka.workout_kind_id
+		WHERE ka.id = ?`, assignmentID).Scan(&resolvedName); err != nil {
+		t.Fatalf("join kind_assignments -> workout_kinds after rebuild: %v", err)
+	}
+	if resolvedName != "Pre-Existing Custom Kind" {
+		t.Fatalf("expected pre-existing kind_assignment to still resolve to 'Pre-Existing Custom Kind' after rebuild, got %q", resolvedName)
+	}
+
+	// FK enforcement must be genuinely active again post-migration: a bogus
+	// workout_kind_id must be rejected, not silently accepted.
+	if _, err := sqlDB.ExecContext(ctx, `
+		INSERT INTO kind_assignments (activity_id, workout_kind_id, assignment_source, status)
+		VALUES (?, 999999, 'rule_engine', 'assigned')`, activityID); err == nil {
+		t.Fatal("expected FK constraint violation for nonexistent workout_kind_id after rebuild, but insert succeeded")
+	}
+}
+
 func contains(s string, substrs ...string) bool {
 	lower := strings.ToLower(s)
 	for _, substr := range substrs {