Implement CE-WP-0005 T01-T08: demo app — sessions, uploads, ZIP archive

Turn the MVP into a self-contained demo. Users now:
  1. Land on an empty-state and create a named session.
  2. Drag-drop or pick arbitrary PDFs into that session.
  3. Annotate, build evidence, link to form fields — all session-scoped.
  4. Export the whole session as a single .zip archive (manifest +
     per-document PDFs).
  5. Import a .zip back — into a new session, or merged into an
     existing one (documents deduped by SHA-256 fingerprint;
     annotations/evidence/links added additively).

Architecture:
- New shared types: SessionId, Session, SessionArchiveManifest +
  parseSessionArchiveManifest with schema-version validation.
- SessionService (engine/services/sessions.ts) handles lifecycle
  (create/rename/delete/setActive) + emits 4 new events through its
  own bus; SharedContracts.md §4 lists the additions.
- SessionProvider (work/SessionContext.tsx) owns the cross-session
  state: service, per-session PdfByteStore registry, per-session
  version counter that drives EngineProvider remounts after imports.
- EngineProvider becomes session-aware (sessionId prop drives per-
  session localStorage keys). Bumping engineRevision after
  restoreFromStorage forces consumers to re-render so restored repos
  show up immediately.
- PdfByteStore (source/pdf/byte-store.ts) holds Uint8Array bytes per
  document and mints blob URLs; ingestPdfFromFile is the upload
  entry-point that wraps the existing ingestPdf pipeline.
- ADR-0008 locks the ZIP layout (manifest.json + documents/<id>.pdf),
  the manifest schema (schemaVersion 1), and the merge-on-collision
  policy. JSZip is the only new dependency.
- App.tsx restructured: SessionProvider at the root, EngineProvider
  keyed by ${sessionId}:${version}, hash routing #/s/<id>[/forms/demo],
  SessionMenu top-bar, CreateFirstSession empty state.
- New DocumentRemoved event for per-document delete cleanup in
  CollectionList; engine.documents.remove() is the new service method.

Tests:
- Unit: 16 SessionService lifecycle + persistence tests;
  per-session snapshot round-trip; PdfByteStore + ingestPdfFromFile;
  SessionArchive parser; exportSessionZip + importSessionZip with
  create + merge + corrupt-archive paths.
- DOM: UploadDropzone, session-scoped CollectionList delete,
  SessionMenu create/switch/rename, routing parser.
- E2E: tests/integration/session-export-reimport.dom.test.tsx walks
  the full create → annotate → export → reimport flow and asserts
  the additive merge (deduped doc + doubled evidence rows).
- Legacy E2Es updated to use a seed-session helper instead of the
  removed fixture-button flow.

Known limitation (documented in ADR-0008): re-importing your own
freshly-exported ZIP creates duplicate annotations. Forward pointer
left for an importBundleId follow-up.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/sessions/SampleSessions.tsx

@@ -0,0 +1,125 @@
+/**
+ * SampleSessions — optional fixture-driven quick-start.
+ *
+ * The MVP collection list (pre-CE-WP-0005) ingested fixture PDFs over
+ * `fetch`. After the session refactor that workflow is no longer the
+ * default; it survives here as an optional way to seed the active
+ * session with a sample document for demo and testing.
+ *
+ * Mounted by `SessionMenu` (T04) under a "Sample sessions ▸" entry
+ * and by the integration tests under CE-WP-0002-T09 / -T05 that need
+ * a known-good document.
+ */
+
+import { useCallback, useState } from "react";
+
+import { ingestPdf } from "@source/index";
+import type { DocumentId } from "@shared/ids";
+import {
+  useActiveDocumentId,
+  useEngine,
+  usePdfByteStore,
+} from "@work/index";
+
+import manifest from "../../../fixtures/pdfs/manifest.json";
+
+interface Fixture {
+  id: string;
+  filename: string;
+  description: string;
+  page_count: number;
+}
+
+const FIXTURES: readonly Fixture[] = (manifest as { fixtures: Fixture[] }).fixtures;
+
+export function SampleSessions() {
+  const engine = useEngine();
+  const byteStore = usePdfByteStore();
+  const { id: activeId, setId } = useActiveDocumentId();
+  const [loadingFixtureId, setLoadingFixtureId] = useState<string | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const [byFixture, setByFixture] = useState<Record<string, DocumentId>>({});
+
+  const handleLoad = useCallback(
+    async (fixture: Fixture) => {
+      setError(null);
+      const existing = byFixture[fixture.id];
+      if (existing) {
+        setId(existing);
+        return;
+      }
+      setLoadingFixtureId(fixture.id);
+      try {
+        const url = `/fixtures/pdfs/${encodeURIComponent(fixture.filename)}`;
+        const response = await fetch(url);
+        if (!response.ok) {
+          throw new Error(`fetch ${url} → ${response.status}`);
+        }
+        const buffer = await response.arrayBuffer();
+        const bytes = new Uint8Array(buffer);
+        const { document, representation } = await ingestPdf(bytes, {
+          filename: fixture.filename,
+        });
+        // Push the bytes into the byte store so the viewer can mount them via
+        // the same blob URL machinery used by the upload path. The document
+        // record carries the blob URL on `uri` for the viewer adapter.
+        const record = byteStore.put(document.id, bytes);
+        engine.documents.register({
+          document: { ...document, uri: record.blobUrl },
+          representation,
+        });
+        setByFixture((prev) => ({ ...prev, [fixture.id]: document.id }));
+        setId(document.id);
+      } catch (err) {
+        setError(err instanceof Error ? err.message : String(err));
+      } finally {
+        setLoadingFixtureId(null);
+      }
+    },
+    [byFixture, byteStore, engine, setId],
+  );
+
+  return (
+    <div data-testid="sample-sessions">
+      <p style={{ fontSize: 12, color: "#555", margin: "0 0 6px" }}>
+        Load a fixture PDF as a sample document for the active session.
+      </p>
+      {error && (
+        <p style={{ fontSize: 12, color: "#b00020", background: "#fff4f4", padding: 6 }}>
+          {error}
+        </p>
+      )}
+      <ul style={{ listStyle: "none", padding: 0, margin: 0 }}>
+        {FIXTURES.map((f) => {
+          const isLoading = loadingFixtureId === f.id;
+          const documentId = byFixture[f.id];
+          const isActive = documentId !== undefined && documentId === activeId;
+          return (
+            <li key={f.id} style={{ marginBottom: 6 }}>
+              <button
+                onClick={() => void handleLoad(f)}
+                disabled={isLoading}
+                style={{
+                  display: "block",
+                  width: "100%",
+                  textAlign: "left",
+                  background: isActive ? "#e8f0ff" : "white",
+                  border: "1px solid #ccc",
+                  padding: 6,
+                  cursor: isLoading ? "wait" : "pointer",
+                  fontSize: 12,
+                }}
+              >
+                <div style={{ fontWeight: 600 }}>{f.id}</div>
+                <div style={{ color: "#666", fontSize: 11 }}>
+                  {f.page_count} page{f.page_count === 1 ? "" : "s"}
+                  {isLoading ? " · loading…" : isActive ? " · open" : ""}
+                </div>
+              </button>
+            </li>
+          );
+        })}
+      </ul>
+    </div>
+  );
+}