M19: deriveStackName cross-references deployed stacks (fix DB-container misattribution)

deriveStackName pure-suffix-stripped on '-' (postgres/db/mariadb/.../cache), so a
stack whose slug ENDS in a role token (e.g. 'my-cache') was misattributed (stripped
to 'my') — filing its DB dump under the wrong/nonexistent stack. Now threads the set
of deployed stack names (m.knownStackNames() <- ListDeployedStacks) into
DiscoverDatabases and cross-references: candidate suffix-strip if known, else the
container name if it IS a known stack, else longest known stack that is a prefix
(handles <stack>_postgres / <stack>-1), else legacy strip. nil/empty known = legacy
behaviour (appexport passes nil). Table test incl. the my-cache case (fails pre-fix).

controller/internal/backup/backup.go

@@ -122,6 +122,20 @@ func (m *Manager) AppNamespaceRoot(stackName string) string {
 	return m.namespaceRoot(drivePath)
 }
 
+// knownStackNames returns the names of all deployed stacks, for M19 DB-container→stack attribution.
+// Empty when no provider is wired (DiscoverDatabases then falls back to legacy suffix-strip).
+func (m *Manager) knownStackNames() []string {
+	if m.stackProvider == nil {
+		return nil
+	}
+	stacks := m.stackProvider.ListDeployedStacks()
+	names := make([]string, 0, len(stacks))
+	for _, s := range stacks {
+		names = append(names, s.Name)
+	}
+	return names
+}
+
 // groupStacksByDrive groups deployed stacks by their home drive path.
 func (m *Manager) groupStacksByDrive() map[string][]StackSummary {
 	if m.stackProvider == nil {
@@ -158,7 +172,7 @@ func (m *Manager) runDBDumpsInternal(ctx context.Context) error {
 	start := time.Now()
 	m.logger.Printf("[INFO] [backup] Starting database dump run")
 
-	dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug())
+	dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug(), m.knownStackNames())
 	if err != nil {
 		m.logger.Printf("[ERROR] [backup] Database discovery failed: %v", err)
 		return err
@@ -415,7 +429,7 @@ func (m *Manager) GetStackHDDMounts(name string) []string {
 // DumpStackDB runs a database dump for containers belonging to a specific stack.
 // Dumps to the stack's home drive: <drive>/backups/primary/<stack>/db-dumps/.
 func (m *Manager) DumpStackDB(ctx context.Context, stackName string) error {
-	dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug())
+	dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug(), m.knownStackNames())
 	if err != nil {
 		return fmt.Errorf("database discovery failed: %w", err)
 	}
@@ -492,7 +506,7 @@ func (m *Manager) RefreshCache(nextDBDump time.Time) {
 
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
-	if dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug()); err == nil {
+	if dbs, err := DiscoverDatabases(ctx, m.logger, m.isDebug(), m.knownStackNames()); err == nil {
 		status.DiscoveredDBs = dbs
 	}