fix(builder): surface proceeding_type id so add-proceeding POST works (t-paliad-345)

The Litigation Builder's "+ Verfahren hinzufügen" silently failed in
prod after t-paliad-343 B2 shipped — clicking a Verfahren chip in the
picker did nothing, no visible error.

Root cause: the wire shape FristenrechnerType (the response of
/api/tools/proceeding-types) carried code+name+nameEN+group but not
id. Builder.ts mountAddProceedingPicker's callback POSTed
`{proceeding_type_id: meta.id}` to
/api/builder/scenarios/{id}/proceedings — meta.id was undefined,
JSON.stringify dropped the key, the server returned 400 ("invalid
input: proceeding_type_id is required"), and fetchJSON swallowed the
error to console. The user saw "nothing happens".

Fix:
- Add `ID int json:"id"` to lp.FristenrechnerType.
- SELECT id in FristenrechnerService.ListProceedings + Scan into the
  new field.
- Defensive guard in builder.ts openAddProceedingPicker — refuse to
  POST without a positive integer id and log a clear error, so a
  future wire-shape regression cannot recreate the silent-fail.
- Regression test in pkg/litigationplanner/types_wire_test.go pins the
  contract (id present in JSON, round-trips as integer).

Side-benefit: fristenrechner-wizard.ts:599-628 documented this exact
gap as a known limitation ("S5/follow-up can extend the wire shape to
include id"). That workaround can now be retired in a follow-up.

Refs m/paliad#153 (Litigation Builder)

frontend/src/client/builder.ts

@@ -855,6 +855,16 @@ function openAddProceedingPicker(anchor: HTMLElement): void {
   if (!state.active) return;
   mountAddProceedingPicker(anchor, state.procTypes, async (meta) => {
     if (!state.active) return;
+    // Guard against a wire-shape regression: if the proceeding-types
+    // endpoint stops returning `id`, `meta.id` is undefined and
+    // JSON.stringify silently drops the field, the server rejects the
+    // POST with a 400, and fetchJSON swallows the error — the user
+    // sees "nothing happens" (t-paliad-345). Fail loud instead.
+    if (typeof meta.id !== "number" || meta.id <= 0) {
+      console.error("builder: missing proceeding_type id in picker meta", meta);
+      setSaveState("error");
+      return;
+    }
     const proc = await addProceeding(state.active.id, {
       proceeding_type_id: meta.id,
     });

internal/services/fristenrechner.go

@@ -145,7 +145,7 @@ func (s *FristenrechnerService) ListProceedings(ctx context.Context, opts Procee
 			  AND pe.event_kind = $%d
 		)`, opts.EventKind)
 	}
-	query := `SELECT code, name, name_en, jurisdiction
+	query := `SELECT id, code, name, name_en, jurisdiction
 		FROM paliad.proceeding_types
 		WHERE ` + strings.Join(where, " AND ") + `
 		ORDER BY sort_order`
@@ -160,7 +160,7 @@ func (s *FristenrechnerService) ListProceedings(ctx context.Context, opts Procee
 	for rows.Next() {
 		var t lp.FristenrechnerType
 		var juris sql.NullString
-		if err := rows.Scan(&t.Code, &t.Name, &t.NameEN, &juris); err != nil {
+		if err := rows.Scan(&t.ID, &t.Code, &t.Name, &t.NameEN, &juris); err != nil {
 			return nil, err
 		}
 		if juris.Valid {

pkg/litigationplanner/types.go

@@ -531,7 +531,17 @@ type RuleCalculationProceeding struct {
 
 // FristenrechnerType mirrors the /api/tools/proceeding-types response
 // metadata.
+//
+// ID is the paliad.proceeding_types primary key. Surfaces so frontend
+// pickers (Litigation Builder add-proceeding, fristenrechner-wizard
+// project prefill) can POST the FK directly without a code→id round
+// trip. Historically code-keyed; the Litigation Builder POSTing
+// proceeding_type_id (int) to /api/builder/scenarios/{id}/proceedings
+// forced surfacing the id (t-paliad-345 — the missing id meant the
+// POST silently sent body={} and the "+ Verfahren hinzufügen" button
+// did nothing).
 type FristenrechnerType struct {
+	ID     int    `json:"id"`
 	Code   string `json:"code"`
 	Name   string `json:"name"`
 	NameEN string `json:"nameEN"`

pkg/litigationplanner/types_wire_test.go

@@ -0,0 +1,50 @@
+package litigationplanner
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+// TestFristenrechnerType_WireShapeIncludesID is the regression test for
+// t-paliad-345: the /api/tools/proceeding-types JSON response must
+// include `id` so frontend pickers (Litigation Builder add-proceeding,
+// fristenrechner-wizard project prefill) can POST proceeding_type_id
+// directly without a code→id round trip. When the id was missing the
+// Litigation Builder "+ Verfahren hinzufügen" button silently dropped
+// the proceeding_type_id from the POST body (JSON.stringify omits
+// undefined keys), the server rejected with 400, and the client
+// swallowed the error — user-visible symptom was "nothing happens".
+func TestFristenrechnerType_WireShapeIncludesID(t *testing.T) {
+	in := FristenrechnerType{
+		ID:     42,
+		Code:   "upc.inf.cfi",
+		Name:   "UPC Verletzungsverfahren",
+		NameEN: "UPC Infringement Action",
+		Group:  "UPC",
+	}
+	b, err := json.Marshal(in)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	got := string(b)
+	if !strings.Contains(got, `"id":42`) {
+		t.Errorf("missing id in wire shape: %s", got)
+	}
+	for _, want := range []string{`"code":"upc.inf.cfi"`, `"nameEN":"UPC Infringement Action"`} {
+		if !strings.Contains(got, want) {
+			t.Errorf("missing %q in wire shape: %s", want, got)
+		}
+	}
+
+	// Round-trip — a client that posts the id back to /api/builder/
+	// scenarios/{id}/proceedings should see it preserved as an integer
+	// (paliad.scenario_proceedings.proceeding_type_id is INT, not UUID).
+	var out FristenrechnerType
+	if err := json.Unmarshal(b, &out); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if out.ID != 42 {
+		t.Errorf("id lost on round-trip: got %d want 42", out.ID)
+	}
+}