feat: extraction coverage — message-granular ledger + token-batched runs (d132373 vision)

THE MESSAGE IS THE UNIT OF COVERAGE (vision-extraction-coverage.md): a
per-chat append-only ledger (coverage.jsonl) records which messages the
pipeline has extracted, by content fingerprint over exactly what the
extraction view sees (one shared line builder — core/coverage.ts); the
uncovered remainder is DERIVED at read time, never dual-tracked. A quiz
answer merging into the asking message re-opens only that message;
plan-block data-part attach never re-opens anything.

- The trigger (turn-service) replaces every-3-quiz-answers with
  uncovered-tokens >= EXTRACTION.chunkTokens (4096) — quiz-less sessions
  extract too, content size is the honest signal.
- runExtraction is now chunked: token-budgeted batches of the oldest
  uncovered consecutive messages (a tool call + result never split), each
  merged batch checkpointing its messages' coverage atomically — an abort
  or error loses at most the in-flight batch; merged batches stay covered.
- Observation refs are batch-tagged (obs:<batchTag>:<sourceId>): re-runs
  of the same batch dedupe; a re-opened message's fresh understanding
  lands as a new event. Fixes the old obs:p1 position-collision.
- New API: GET /api/graph/coverage (exact per-session derived coverage +
  running flags, most-uncovered first) and POST /api/graph/coverage/extract
  (manual run for one session, 409 while in flight).
- Graph view chrome: the coverage button opens a panel with every
  session's covered/uncovered tokens and a per-session Extract button —
  the manual answer to aborted runs, errors, and dormant tails. Renders
  even when the graph is empty: an empty graph with uncovered sessions is
  exactly when it matters. Polls only while open.
- Notes imports keep the whole-file checkpoint path (coverage undefined).
- Tests: pure-core coverage suite (11), chunked-pipeline suite (3:
  multi-batch + no-op, abort-keeps-earlier-batches + remainder re-run,
  re-open alone + data-part invisibility), panel render suite (5);
  pendingQuizAnswers and its tests deleted as dead code. 486/486.

Live-smoked on real GLM: manual extract of "teach me modal realism" ran
one batch, wrote 4 coverage entries, panel flipped to "1.3k covered ·
complete" with the button disabled, graph refetched (nodes 11), usage
persisted with real stats.

app/api/graph/coverage/route.ts

@@ -0,0 +1,40 @@
+/**
+ * GET /api/graph/coverage — the exact extraction coverage of every session
+ * (vision-extraction-coverage.md, settled 2026-09-15): which sessions have
+ * unextracted content, how much (tokens + message counts), and which runs
+ * are in flight. "Uncovered" is DERIVED here per request — fingerprint the
+ * current transcript, diff against the coverage ledger — never tracked as
+ * a second ledger. This is the data behind the graph view's coverage panel
+ * and its per-session "extract what's missing" buttons.
+ */
+import type { UIMessage } from "ai";
+import { chatStore, extractionStatuses, stores } from "@/src/server";
+import { coverageOf } from "@/src/core";
+
+export const dynamic = "force-dynamic";
+
+export async function GET() {
+	const running = new Set(
+		extractionStatuses().filter((run) => run.kind === "chat").map((run) => run.chatId),
+	);
+	const entries = stores.graphStore.readCoverage();
+	const chats = chatStore.listChats().map((summary) => {
+		const record = chatStore.getChat(summary.id);
+		const messages = (record?.messages ?? []) as UIMessage[];
+		const cov = coverageOf(messages, entries, summary.id);
+		return {
+			chatId: summary.id,
+			title: summary.title,
+			updatedAt: summary.updatedAt,
+			totalMessages: cov.slots.length,
+			coveredMessages: cov.coveredCount,
+			uncoveredMessages: cov.uncoveredCount,
+			coveredTokens: cov.coveredTokens,
+			uncoveredTokens: cov.uncoveredTokens,
+			running: running.has(summary.id),
+		};
+	});
+	// Most uncovered first — the actionable sessions lead the panel.
+	chats.sort((a, b) => b.uncoveredTokens - a.uncoveredTokens || (a.updatedAt < b.updatedAt ? 1 : -1));
+	return Response.json({ chats });
+}