feat(approvals): t-paliad-216 — server-side hydration for back-link

Server-side additions so /inbox can render the suggest-changes back-link
without an extra client round-trip:

  - ApprovalRequestView gains NextRequestID. Hydrated via correlated
    subquery on previous_request_id; mig 103's partial index makes the
    lookup O(1) per row.
  - view_service.go approvalRowSubtitle picks up the changes_requested
    case ("Abgelehnt mit Vorschlag von <decider>").
  - filter_spec.go validRequestStatuses includes "changes_requested" so
    user-views can filter on it.
  - handlers/approvals.go isValidInboxStatus accepts "changes_requested"
    on the /api/inbox/{mine,pending-mine}?status= query. Test case added
    to TestParseInboxFilter_DropsUnknownStatus.

internal/handlers/approvals.go

@@ -270,7 +270,8 @@ func isValidInboxStatus(s string) bool {
 		services.RequestStatusApproved,
 		services.RequestStatusRejected,
 		services.RequestStatusRevoked,
-		services.RequestStatusSuperseded:
+		services.RequestStatusSuperseded,
+		services.RequestStatusChangesRequested:
 		return true
 	}
 	return false

internal/handlers/approvals_test.go

@@ -135,6 +135,7 @@ func TestParseInboxFilter_DropsUnknownStatus(t *testing.T) {
 		{"rejected", "rejected"},
 		{"revoked", "revoked"},
 		{"superseded", "superseded"},
+		{"changes_requested", "changes_requested"}, // t-paliad-216
 		{"foo", ""},                // unknown — dropped
 		{"DROP+TABLE", ""},         // hostile — dropped
 		{"PENDING", ""},            // case mismatch — dropped (we don't normalise)

internal/services/approval_service.go

@@ -1080,14 +1080,20 @@ func marshalJSONOrNull(m map[string]any) ([]byte, error) {
 // server would reject, replacing the previous click-then-alert UX.
 type ApprovalRequestView struct {
 	models.ApprovalRequest
-	ProjectTitle      string  `db:"project_title"       json:"project_title"`
-	EntityTitle       *string `db:"entity_title"        json:"entity_title,omitempty"`
-	RequesterName     string  `db:"requester_name"      json:"requester_name"`
-	RequesterEmail    string  `db:"requester_email"     json:"requester_email"`
-	DeciderName       *string `db:"decider_name"        json:"decider_name,omitempty"`
-	DeciderEmail      *string `db:"decider_email"       json:"decider_email,omitempty"`
-	ViewerCanApprove  bool    `db:"viewer_can_approve"  json:"viewer_can_approve"`
-	ViewerIsRequester bool    `db:"viewer_is_requester" json:"viewer_is_requester"`
+	ProjectTitle      string     `db:"project_title"       json:"project_title"`
+	EntityTitle       *string    `db:"entity_title"        json:"entity_title,omitempty"`
+	RequesterName     string     `db:"requester_name"      json:"requester_name"`
+	RequesterEmail    string     `db:"requester_email"     json:"requester_email"`
+	DeciderName       *string    `db:"decider_name"        json:"decider_name,omitempty"`
+	DeciderEmail      *string    `db:"decider_email"       json:"decider_email,omitempty"`
+	ViewerCanApprove  bool       `db:"viewer_can_approve"  json:"viewer_can_approve"`
+	ViewerIsRequester bool       `db:"viewer_is_requester" json:"viewer_is_requester"`
+	// NextRequestID is the forward-pointer from a changes_requested row
+	// to the new pending row spawned by SuggestChanges (t-paliad-216).
+	// Hydrated via correlated subquery on previous_request_id; the
+	// partial index approval_requests_previous_idx keeps the lookup O(1).
+	// NULL on every row that hasn't been counter-proposed.
+	NextRequestID *uuid.UUID `db:"next_request_id"     json:"next_request_id,omitempty"`
 }
 
 // approvalEligibilitySQL is the SELECT-and-WHERE-compatible boolean
@@ -1150,7 +1156,11 @@ const approvalRequestViewColumns = `
     du.display_name                     AS decider_name,
     du.email                            AS decider_email,
     (ar.status = 'pending' AND ar.requested_by <> $1 AND ` + approvalEligibilitySQL + `) AS viewer_can_approve,
-    (ar.requested_by = $1)              AS viewer_is_requester`
+    (ar.requested_by = $1)              AS viewer_is_requester,
+    (SELECT nxt.id FROM paliad.approval_requests nxt
+       WHERE nxt.previous_request_id = ar.id
+       ORDER BY nxt.requested_at DESC
+       LIMIT 1)                          AS next_request_id`
 
 const approvalRequestViewJoins = `
     paliad.approval_requests ar

internal/services/filter_spec.go

@@ -203,7 +203,7 @@ var KnownProjectEventKinds = []string{
 // filters and request-side status filters respectively.
 var (
 	validEntityApprovalStatuses  = []string{"approved", "pending", "legacy"}
-	validRequestStatuses         = []string{"pending", "approved", "rejected", "revoked"}
+	validRequestStatuses         = []string{"pending", "approved", "rejected", "revoked", "changes_requested"}
 	validApprovalEntityTypes     = []string{"deadline", "appointment"}
 	validApprovalViewerRoles     = []string{"approver_eligible", "self_requested", "any_visible"}
 	validDeadlineStatuses        = []string{"pending", "completed"}

internal/services/view_service.go

@@ -569,6 +569,11 @@ func approvalRowSubtitle(r ApprovalRequestView) string {
 		return "Abgelehnt"
 	case "revoked":
 		return "Widerrufen"
+	case "changes_requested":
+		if r.DeciderName != nil {
+			return fmt.Sprintf("Abgelehnt mit Vorschlag von %s", *r.DeciderName)
+		}
+		return "Abgelehnt mit Vorschlag"
 	}
 	return r.Status
 }