feat(t-paliad-122): GET /api/tools/courts + Fristenrechner court picker

GET /api/tools/courts[?courtType=UPC-LD] returns the deadline-
computation slice of paliad.courts (id, code, names, country, regime,
court_type) — distinct from the rich Gerichtsverzeichnis at
/api/courts. Optional courtType filter narrows to a single tier.

POST /api/tools/fristenrechner and POST /api/tools/fristenrechner/
calculate-rule both accept an optional courtId field. When set, the
calculator resolves the court's (country, regime) and uses that
calendar; when omitted, the proceeding's existing jurisdiction column
seeds a sensible default — preserves today's behaviour for callers
that don't yet send a court.

Frontend: court-picker-row added to step 2 of the Fristenrechner
wizard. Visible only for proceeding types with multiple compatible
courts (today: every UPC-flavoured proceeding — UPC LDs span 12
countries, plus UPC CD seats and the CoA). DE-only proceedings (BPatG
nullity, BGH appeals, DPMA, EPA, EP grant) keep the form unchanged.
Picker re-runs the calc on selection so the user sees the same
deadlines shift to a different calendar without a manual click. i18n
key deadlines.court.label added for both DE and EN.

Default courts wired sensibly: UPC_INF / UPC_REV / UPC_PI etc. → UPC
LD München (HLC's home venue); UPC_APP / UPC_APP_ORDERS /
UPC_COST_APPEAL → UPC CoA Luxembourg; UPC_REV → UPC CD Paris.

frontend/src/client/fristenrechner.ts

@@ -226,6 +226,15 @@ async function calculate() {
   const overrides: Record<string, string> = {};
   for (const [code, date] of anchorOverrides) overrides[code] = date;
 
+  // Court picker — only meaningful when the picker row is visible
+  // (multi-court proceeding types). When hidden, server resolves the
+  // default for the proceeding's jurisdiction.
+  const courtPickerRow = document.getElementById("court-picker-row");
+  const courtPicker = document.getElementById("court-picker") as HTMLSelectElement | null;
+  const courtId = courtPickerRow && courtPickerRow.style.display !== "none" && courtPicker?.value
+    ? courtPicker.value
+    : "";
+
   try {
     const resp = await fetch("/api/tools/fristenrechner", {
       method: "POST",
@@ -236,6 +245,7 @@ async function calculate() {
         priorityDate: priorityDate || undefined,
         flags: flags.length > 0 ? flags : undefined,
         anchorOverrides: Object.keys(overrides).length > 0 ? overrides : undefined,
+        courtId: courtId || undefined,
       }),
     });
 
@@ -721,11 +731,104 @@ function selectProceeding(btn: HTMLButtonElement) {
   if (revCciRow) revCciRow.style.display = selectedType === "UPC_REV" ? "" : "none";
 
   syncInfAmendEnabled();
+  populateCourtPicker(selectedType);
 
   showStep(2);
   scheduleProcCalc(0);
 }
 
+// Court picker — t-paliad-122. Visible only for proceeding types that can
+// land in multiple courts with different holiday calendars (today: every
+// UPC-flavoured proceeding type, since UPC LDs span DE/FR/IT/NL/BE/FI/PT/
+// AT/SI/DK + Stockholm RD + 3 CD seats). For DE-only proceedings (DE_NULL,
+// DE_NULL_BGH, DE_INF_BGH, DPMA_*, EPA_*, EP_GRANT) the court is fixed by
+// the proceeding type — no picker, server resolves the default.
+//
+// The picker calls /api/tools/courts?courtType=UPC-LD on first need and
+// caches the response per-type. Defaulting to upc-ld-muenchen matches HLC's
+// most common venue and keeps current behaviour for users who don't choose.
+interface CourtRow {
+  id: string;
+  code: string;
+  nameDE: string;
+  nameEN: string;
+  country: string;
+  regime?: string;
+  courtType: string;
+}
+
+const courtCache = new Map<string, CourtRow[]>();
+
+function courtTypesFor(proceedingType: string): string[] {
+  // Map proceeding code to compatible court types. UPC proceedings → UPC-LD
+  // (most common); appeals → UPC-CoA; central-division revocations → UPC-CD.
+  if (proceedingType === "UPC_APP" || proceedingType === "UPC_APP_ORDERS" || proceedingType === "UPC_COST_APPEAL") {
+    return ["UPC-CoA"];
+  }
+  if (proceedingType === "UPC_REV") {
+    return ["UPC-CD", "UPC-LD"]; // CD is the default revocation forum, LD when joined with infringement
+  }
+  if (proceedingType.startsWith("UPC_")) {
+    return ["UPC-LD"];
+  }
+  return [];
+}
+
+function defaultCourtFor(proceedingType: string): string {
+  if (proceedingType === "UPC_APP" || proceedingType === "UPC_APP_ORDERS" || proceedingType === "UPC_COST_APPEAL") {
+    return "upc-coa-luxembourg";
+  }
+  if (proceedingType === "UPC_REV") {
+    return "upc-cd-paris";
+  }
+  return "upc-ld-muenchen";
+}
+
+async function fetchCourts(courtType: string): Promise<CourtRow[]> {
+  if (courtCache.has(courtType)) return courtCache.get(courtType)!;
+  try {
+    const resp = await fetch(`/api/tools/courts?courtType=${encodeURIComponent(courtType)}`);
+    if (!resp.ok) return [];
+    const rows = (await resp.json()) as CourtRow[];
+    courtCache.set(courtType, rows);
+    return rows;
+  } catch {
+    return [];
+  }
+}
+
+async function populateCourtPicker(proceedingType: string): Promise<void> {
+  const row = document.getElementById("court-picker-row");
+  const select = document.getElementById("court-picker") as HTMLSelectElement | null;
+  if (!row || !select) return;
+
+  const types = courtTypesFor(proceedingType);
+  if (types.length === 0) {
+    row.style.display = "none";
+    select.innerHTML = "";
+    return;
+  }
+
+  // Load all compatible court types and concatenate (CD before LD for REV).
+  const lists = await Promise.all(types.map(t => fetchCourts(t)));
+  const courts = lists.flat();
+  if (courts.length <= 1) {
+    // Single compatible court — no point asking the user. Server's
+    // jurisdiction default lands the same place.
+    row.style.display = "none";
+    select.innerHTML = "";
+    return;
+  }
+
+  const lang = getLang();
+  const defaultID = defaultCourtFor(proceedingType);
+  select.innerHTML = courts.map(c => {
+    const name = lang === "en" ? c.nameEN : c.nameDE;
+    return `<option value="${escAttr(c.id)}"${c.id === defaultID ? " selected" : ""}>${escHtml(name)}</option>`;
+  }).join("");
+  row.style.display = "";
+}
+
 // inf-amend-flag is only meaningful when ccr-flag is on (R.30 application
 // is filed within the Defence to CCR). When ccr-flag flips off, also
 // untick inf-amend-flag so the calc payload stays coherent.
@@ -807,6 +910,8 @@ document.addEventListener("DOMContentLoaded", () => {
   if (revAmendFlag) revAmendFlag.addEventListener("change", () => scheduleProcCalc(0));
   const revCciFlag = document.getElementById("rev-cci-flag") as HTMLInputElement | null;
   if (revCciFlag) revCciFlag.addEventListener("change", () => scheduleProcCalc(0));
+  const courtPicker = document.getElementById("court-picker") as HTMLSelectElement | null;
+  if (courtPicker) courtPicker.addEventListener("change", () => scheduleProcCalc(0));
 
   // Click-to-edit on timeline / column dates: open an inline date input
   // and persist the user's choice as an anchor override so downstream

frontend/src/client/i18n.ts

@@ -211,6 +211,7 @@ const translations: Record<Lang, Record<string, string>> = {
     "deadlines.trigger.date": "Datum:",
     "deadlines.trigger.label": "Ausgangsdatum",
     "deadlines.priority.date": "Priorit\u00e4tstag (optional):",
+    "deadlines.court.label": "Gericht:",
     "deadlines.flag.ccr": "Mit Widerklage auf Nichtigkeit",
     "deadlines.flag.inf_amend": "Mit Antrag auf Patentänderung (R.30)",
     "deadlines.flag.rev_amend": "Mit Antrag auf Patentänderung (R.49.2.a)",
@@ -1806,6 +1807,7 @@ const translations: Record<Lang, Record<string, string>> = {
     "deadlines.trigger.date": "Date:",
     "deadlines.trigger.label": "Trigger date",
     "deadlines.priority.date": "Priority date (optional):",
+    "deadlines.court.label": "Court:",
     "deadlines.flag.ccr": "Counterclaim for revocation filed",
     "deadlines.flag.inf_amend": "Application to amend the patent filed (R.30)",
     "deadlines.flag.rev_amend": "Application to amend the patent filed (R.49.2.a)",

frontend/src/fristenrechner.tsx

@@ -282,6 +282,10 @@ export function renderFristenrechner(): string {
                       <label htmlFor="trigger-date" className="date-label" data-i18n="deadlines.trigger.date">Datum:</label>
                       <input type="date" id="trigger-date" className="date-input" value={today} />
                     </div>
+                    <div className="date-field-row" id="court-picker-row" style="display:none">
+                      <label htmlFor="court-picker" className="date-label" data-i18n="deadlines.court.label">Gericht:</label>
+                      <select id="court-picker" className="date-input"></select>
+                    </div>
                     <div className="date-field-row" id="priority-date-row" style="display:none">
                       <label htmlFor="priority-date" className="date-label" data-i18n="deadlines.priority.date">Priorit&auml;tstag (optional):</label>
                       <input type="date" id="priority-date" className="date-input" />

frontend/src/i18n-keys.ts

@@ -569,6 +569,7 @@ export type I18nKey =
   | "deadlines.col.status"
   | "deadlines.col.title"
   | "deadlines.complete.action"
+  | "deadlines.court.label"
   | "deadlines.court.set"
   | "deadlines.date.edit.hint"
   | "deadlines.de"

internal/handlers/fristenrechner.go

@@ -31,6 +31,7 @@ func handleFristenrechnerAPI(w http.ResponseWriter, r *http.Request) {
 		PriorityDate    string            `json:"priorityDate,omitempty"`
 		Flags           []string          `json:"flags,omitempty"`
 		AnchorOverrides map[string]string `json:"anchorOverrides,omitempty"`
+		CourtID         string            `json:"courtId,omitempty"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "Ungültige Anfrage"})
@@ -45,6 +46,7 @@ func handleFristenrechnerAPI(w http.ResponseWriter, r *http.Request) {
 		PriorityDateStr: req.PriorityDate,
 		Flags:           req.Flags,
 		AnchorOverrides: req.AnchorOverrides,
+		CourtID:         req.CourtID,
 	})
 	if err != nil {
 		if errors.Is(err, services.ErrUnknownProceedingType) {
@@ -81,6 +83,7 @@ func handleFristenrechnerCalculateRule(w http.ResponseWriter, r *http.Request) {
 		RuleLocalCode  string   `json:"ruleLocalCode"`
 		TriggerDate    string   `json:"triggerDate"`
 		Flags          []string `json:"flags,omitempty"`
+		CourtID        string   `json:"courtId,omitempty"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "Ungültige Anfrage"})
@@ -103,6 +106,7 @@ func handleFristenrechnerCalculateRule(w http.ResponseWriter, r *http.Request) {
 		RuleLocalCode:  req.RuleLocalCode,
 		TriggerDate:    req.TriggerDate,
 		Flags:          req.Flags,
+		CourtID:        req.CourtID,
 	})
 	if err != nil {
 		switch {
@@ -187,3 +191,33 @@ func handleEventDeadlinesCalculate(w http.ResponseWriter, r *http.Request) {
 	}
 	writeJSON(w, http.StatusOK, resp)
 }
+
+// GET /api/tools/courts — list active courts for the Fristenrechner court
+// picker. Optional ?courtType=UPC-LD filter narrows to a single tier so the
+// UI can render only the courts compatible with the selected proceeding.
+// Returns the deadline-computation slice (id, code, names, country, regime,
+// court_type, sort_order) — NOT the full Gerichtsverzeichnis catalog. The
+// rich addresses / phone / languages payload still lives at /api/courts.
+func handleCourtsList(w http.ResponseWriter, r *http.Request) {
+	if dbSvc == nil || dbSvc.courts == nil {
+		writeJSON(w, http.StatusServiceUnavailable, map[string]string{
+			"error": "Gerichte vorübergehend nicht verfügbar (keine Datenbank).",
+		})
+		return
+	}
+	courtType := r.URL.Query().Get("courtType")
+	var (
+		courts []services.Court
+		err    error
+	)
+	if courtType != "" {
+		courts, err = dbSvc.courts.ByCourtType(courtType)
+	} else {
+		courts, err = dbSvc.courts.All()
+	}
+	if err != nil {
+		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "konnte Gerichte nicht laden"})
+		return
+	}
+	writeJSON(w, http.StatusOK, courts)
+}

internal/handlers/handlers.go

@@ -140,6 +140,7 @@ func Register(mux *http.ServeMux, client *auth.Client, giteaAPIToken string, svc
 	protected.HandleFunc("GET /api/tools/proceeding-types", handleProceedingTypes)
 	protected.HandleFunc("GET /api/tools/trigger-events", handleTriggerEventsList)
 	protected.HandleFunc("POST /api/tools/event-deadlines", handleEventDeadlinesCalculate)
+	protected.HandleFunc("GET /api/tools/courts", handleCourtsList)
 	protected.HandleFunc("GET /api/tools/fristenrechner/search", handleFristenrechnerSearch)
 	protected.HandleFunc("GET /api/tools/fristenrechner/event-categories", handleFristenrechnerEventCategories)
 	protected.HandleFunc("GET /downloads", handleDownloadsPage)