feat(pdf): extract standalone PDF ingest package (ESRC-WP-0001)

Bootstrap evidence-source from the citation-evidence src/source PDF slice.

- Headless core (src/pdf): ingest/extract/fingerprint, importing domain
  contracts from @citation-evidence/engine/shared (no local copies)
- Browser upload helpers isolated under src/browser behind a ./browser
  entry point, with an eslint boundary keeping the core browser-free
- pnpm/TS/vitest/eslint scaffold; 52 tests (contract + determinism)
- Fixtures resolved from the sibling citation-evidence checkout, not
  duplicated (real PII) — see docs/ADR-0002; suites skip when absent
- Boundary + fixture decisions recorded as docs/ADR-0001 / ADR-0002
- README/SCOPE rewritten; capability.infotech.pdf-evidence-ingest
  registered, NO_CAPABILITIES removed
- Follow-on workplans ESRC-WP-0002..0004 queued; ESRC-WP-0001 finished

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/browser/byte-store.ts

@@ -0,0 +1,115 @@
+/**
+ * `PdfByteStore` — in-memory store for uploaded PDF bytes, keyed by
+ * `DocumentId`.
+ *
+ * BROWSER SURFACE — not part of the headless ingest core. This mints and
+ * revokes `blob:` URLs and is meant to back an interactive upload/viewer
+ * session. Headless callers should use `src/pdf/` directly and never import
+ * this module.
+ *
+ * Uploaded PDFs are stored in memory only. Bytes survive within a tab
+ * session; reloading the page loses them unless the session was exported.
+ *
+ * One store instance per active session. The session-management layer is
+ * responsible for swapping the active store when the user switches sessions.
+ * The store also owns a small registry of issued `blob:` URLs so it can
+ * revoke them on delete/clear — no cross-cutting cleanup at the app layer.
+ */
+
+import type { DocumentId } from "@citation-evidence/engine/shared";
+
+export interface PdfByteRecord {
+  readonly bytes: Uint8Array;
+  /** A `blob:` URL the viewer can consume directly. */
+  readonly blobUrl: string;
+}
+
+export interface PdfByteStore {
+  put(documentId: DocumentId, bytes: Uint8Array): PdfByteRecord;
+  get(documentId: DocumentId): PdfByteRecord | null;
+  has(documentId: DocumentId): boolean;
+  delete(documentId: DocumentId): boolean;
+  list(): readonly DocumentId[];
+  /** Revoke every blob URL and clear the store. */
+  clear(): void;
+  /** Total bytes currently held — useful for UI dashboards. */
+  size(): number;
+}
+
+export interface CreatePdfByteStoreOptions {
+  /**
+   * Mint a URL for the given bytes. Defaults to `URL.createObjectURL` in
+   * environments that have it; tests can inject a deterministic stub.
+   */
+  readonly createObjectURL?: (blob: Blob) => string;
+  /** Revoke a URL previously minted by `createObjectURL`. */
+  readonly revokeObjectURL?: (url: string) => void;
+}
+
+export function createPdfByteStore(
+  options: CreatePdfByteStoreOptions = {},
+): PdfByteStore {
+  const createUrl =
+    options.createObjectURL ??
+    ((blob: Blob) => {
+      if (typeof URL === "undefined" || typeof URL.createObjectURL !== "function") {
+        throw new Error(
+          "createPdfByteStore: URL.createObjectURL not available — inject a stub via options",
+        );
+      }
+      return URL.createObjectURL(blob);
+    });
+  const revokeUrl =
+    options.revokeObjectURL ??
+    ((url: string) => {
+      if (typeof URL !== "undefined" && typeof URL.revokeObjectURL === "function") {
+        URL.revokeObjectURL(url);
+      }
+    });
+
+  const records = new Map<DocumentId, PdfByteRecord>();
+
+  return {
+    put(documentId, bytes) {
+      // Replace previous record (revoking the prior URL) if any.
+      const prior = records.get(documentId);
+      if (prior) revokeUrl(prior.blobUrl);
+      // Cast: Blob() does accept Uint8Array at runtime, but TS narrows the
+      // buffer type to ArrayBufferLike (could be SharedArrayBuffer) and
+      // refuses without help. The bytes here always come from a fresh
+      // arrayBuffer() call, so a regular ArrayBuffer is guaranteed.
+      const blob = new Blob([bytes as unknown as ArrayBuffer], {
+        type: "application/pdf",
+      });
+      const blobUrl = createUrl(blob);
+      const record: PdfByteRecord = { bytes, blobUrl };
+      records.set(documentId, record);
+      return record;
+    },
+    get(documentId) {
+      return records.get(documentId) ?? null;
+    },
+    has(documentId) {
+      return records.has(documentId);
+    },
+    delete(documentId) {
+      const record = records.get(documentId);
+      if (!record) return false;
+      revokeUrl(record.blobUrl);
+      records.delete(documentId);
+      return true;
+    },
+    list() {
+      return [...records.keys()];
+    },
+    clear() {
+      for (const record of records.values()) revokeUrl(record.blobUrl);
+      records.clear();
+    },
+    size() {
+      let total = 0;
+      for (const r of records.values()) total += r.bytes.byteLength;
+      return total;
+    },
+  };
+}