Precedent attachment UI in the compose screen

Surface the new POST/GET/DELETE /api/cases/{n}/precedents endpoints
in the compose screen as two insertion points:

1. A new case-level card "פסיקה כללית לדיון" at the top of the
   main column, for precedents that support the discussion intro
   rather than a specific threshold_claim / issue.
2. An inline "פסיקה תומכת" section inside each SubsectionCard,
   below the ChairEditor.

Both insertion points render a `<PrecedentsSection>` which shows a
list of `<PrecedentCard>` (citation + blockquote + optional chair
note + 📄 chip if a PDF was archived) followed by a `<PrecedentAttacher>`
popover trigger.

The Attacher is a Popover with cross-case typeahead: typing 2+
characters into the citation field hits /api/precedents/search and
shows distinct library matches; picking one prefills quote + chair
note but leaves them editable so customizing the quote for this
case doesn't mutate the library. An optional PDF/DOCX/DOC file can
be attached — it uploads first via POST .../upload-pdf and the
returned document_id is passed into the precedent create call.

The parent compose page issues a single useCasePrecedents query
and partitions the result by section_id into a Map so each
SubsectionCard renders its own slice without re-fetching.

shadcn Popover installed as a new primitive. sonner toasts wired
for success/error in both attach and delete flows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-ui/src/lib/api/precedents.ts

@@ -0,0 +1,140 @@
+/**
+ * Attached-precedent hooks — user-supplied case-law quotes that
+ * justify chair positions in the compose screen.
+ *
+ * Backed by POST/GET/DELETE /api/cases/{n}/precedents and the
+ * cross-case library search at GET /api/precedents/search. The
+ * optional PDF archive chains through POST .../upload-pdf before
+ * precedent creation; that's a plain async function, not a mutation
+ * hook, because it has no cache invalidation of its own.
+ */
+
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import { apiRequest, ApiError } from "./client";
+import type { PracticeArea } from "@/lib/practice-area";
+
+export type CasePrecedent = {
+  id: string;
+  case_id: string;
+  section_id: string | null;
+  quote: string;
+  citation: string;
+  chair_note: string;
+  pdf_document_id: string | null;
+  practice_area: PracticeArea | null;
+  created_at: string;
+  updated_at: string;
+};
+
+export type PrecedentCreateInput = {
+  quote: string;
+  citation: string;
+  section_id?: string;
+  chair_note?: string;
+  pdf_document_id?: string;
+};
+
+export type LibraryMatch = {
+  id: string;
+  citation: string;
+  quote: string;
+  chair_note: string;
+  practice_area: PracticeArea | null;
+  created_at: string;
+};
+
+export const precedentKeys = {
+  all: ["precedents"] as const,
+  forCase: (caseNumber: string) =>
+    [...precedentKeys.all, "case", caseNumber] as const,
+  librarySearch: (q: string, area: string) =>
+    [...precedentKeys.all, "library", area, q] as const,
+};
+
+export function useCasePrecedents(caseNumber: string | undefined) {
+  return useQuery({
+    queryKey: precedentKeys.forCase(caseNumber ?? ""),
+    queryFn: ({ signal }) =>
+      apiRequest<CasePrecedent[]>(
+        `/api/cases/${caseNumber}/precedents`,
+        { signal },
+      ),
+    enabled: Boolean(caseNumber),
+    staleTime: 30_000,
+  });
+}
+
+export function useCreatePrecedent(caseNumber: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (input: PrecedentCreateInput) =>
+      apiRequest<CasePrecedent>(`/api/cases/${caseNumber}/precedents`, {
+        method: "POST",
+        body: input,
+      }),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: precedentKeys.forCase(caseNumber) });
+      qc.invalidateQueries({ queryKey: [...precedentKeys.all, "library"] });
+    },
+  });
+}
+
+export function useDeletePrecedent(caseNumber: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (precedentId: string) =>
+      apiRequest<{ deleted: boolean }>(`/api/precedents/${precedentId}`, {
+        method: "DELETE",
+      }),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: precedentKeys.forCase(caseNumber) });
+    },
+  });
+}
+
+export function usePrecedentLibrarySearch(
+  query: string,
+  practiceArea: PracticeArea | null | undefined,
+  enabled: boolean,
+) {
+  return useQuery({
+    queryKey: precedentKeys.librarySearch(query, practiceArea ?? ""),
+    queryFn: ({ signal }) => {
+      const params = new URLSearchParams({ q: query });
+      if (practiceArea) params.set("practice_area", practiceArea);
+      return apiRequest<LibraryMatch[]>(
+        `/api/precedents/search?${params.toString()}`,
+        { signal },
+      );
+    },
+    enabled: enabled && query.trim().length >= 2,
+    staleTime: 10_000,
+    placeholderData: (prev) => prev,
+  });
+}
+
+/**
+ * One-shot PDF archive upload. Returns the new document_id so the
+ * caller can pass it into useCreatePrecedent. No cache invalidation
+ * — we only care about the id as a handle.
+ */
+export async function uploadPrecedentPdf(
+  caseNumber: string,
+  file: File,
+): Promise<{ document_id: string; filename: string }> {
+  const fd = new FormData();
+  fd.append("file", file);
+  const res = await fetch(
+    `/api/cases/${encodeURIComponent(caseNumber)}/precedents/upload-pdf`,
+    { method: "POST", body: fd },
+  );
+  const parsed = await res.json().catch(() => null);
+  if (!res.ok) {
+    throw new ApiError(
+      `Upload failed with ${res.status}`,
+      res.status,
+      parsed,
+    );
+  }
+  return parsed as { document_id: string; filename: string };
+}