Notes front door: format-agnostic import into the graph pipeline

The same extractor→auditor→merger pipeline now runs over raw personal
notes in arbitrary formats (vision §1, DECIDED 2026-09-13):

- NotesSource records (data/graph/sources.json, deterministic id from
  path hash → idempotent re-imports) play the chatId role in mappings,
  checkpoints, and observation events; usage lands on the source record
  (appendSourceUsage, idempotent per startedAt, kept across upserts).
- mergeFindings is chat-store-free: callers pass MergeSource
  {messages, foldedAt} — sessions pass the chat record, notes pass
  messages:null (no quiz-event rebuild; a deterministic rebuild needs
  structured quiz tool parts).
- Second extractor prompt (NOTES_EXTRACTOR_INSTRUCTIONS) for general-
  purpose extraction; understanding judges the AUTHOR's grasp. Auditor
  wording input-agnostic. extract/audit share one generic runSubmitAgent.
- graphSnapshot.fileSources (srcId→filePath); notes sources render as
  static path entries in the detail card (FileTextIcon, never a link).
- One shared pipeline instance (exported from chat-handler): same
  single-flight registry, live status chips (label = file path), usage
  accounting, and true abort for both front doors.
- Transport: POST /api/graph/import (multipart, 3-wide worker pool) +
  Import notes… button in the graph view; scripts/import-notes.ts for
  batch runs (concurrency 4).
- real-data-extraction/ gitignored (raw import sources never committed).

355/355 tests; typecheck, lint, build green.

tests/usage.test.ts

@@ -10,7 +10,8 @@ import test from "node:test";
 import * as fs from "node:fs";
 
 import { chatStore } from "../src/store/chats.ts";
-import { PATHS } from "../config.ts";
+import { graphStore } from "../src/store/graph.ts";
+import { PATHS, SOURCES_FILE } from "../config.ts";
 import { callCost, contextWindow, jobCost, sessionCost, sumSteps, turnCost } from "../src/core/prices.ts";
 import type { CallUsage, ExtractionRunUsage, JobRecord, TurnUsage } from "../src/core/contracts.ts";
 
@@ -170,3 +171,40 @@ test("appendExtractionUsage: appends, idempotent per startedAt, not in list payl
 
 	fs.unlinkSync(`${PATHS.chats}/${record.id}.json`);
 });
+
+test("appendSourceUsage: appends to the source record, idempotent per startedAt, upsert keeps history", () => {
+	// The real fs graphStore — sources.json backed up and restored around
+	// this test (same discipline as the chat fixture files).
+	fs.mkdirSync(PATHS.graph, { recursive: true });
+	let bak: string | undefined;
+	if (fs.existsSync(SOURCES_FILE)) bak = `${SOURCES_FILE}.w5test.bak`;
+	if (bak) fs.renameSync(SOURCES_FILE, bak);
+	try {
+		const runEntry = (startedAt: number): ExtractionRunUsage => ({
+			startedAt,
+			at: "2026-09-13T00:00:00Z",
+			durationMs: 42_000,
+			stats: { nodes: 1, edges: 2, events: 3 },
+			stages: {
+				extractor: { model: "z-ai/glm-5.3-flash", steps: [call({ inputTokens: 100, outputTokens: 10 })] },
+				auditor: { model: "z-ai/glm-5.3-flash", steps: [call({ inputTokens: 50, outputTokens: 5 })] },
+			},
+		});
+		const id = "src_usagetest01";
+		graphStore.upsertSource({ id, filePath: "/vault/usagetest.md", importedAt: "2026-09-13T00:00:00Z" });
+		graphStore.appendSourceUsage(id, runEntry(1));
+		graphStore.appendSourceUsage(id, runEntry(1)); // same run appended twice → no-op
+		graphStore.appendSourceUsage(id, runEntry(2)); // a retried run is a NEW spend
+		assert.equal(graphStore.readSources().find((s) => s.id === id)?.extractions?.length, 2);
+
+		// An upsert (re-import) KEEPS the usage history.
+		graphStore.upsertSource({ id, filePath: "/vault/usagetest.md", importedAt: "2026-09-14T00:00:00Z" });
+		assert.equal(graphStore.readSources().find((s) => s.id === id)?.extractions?.length, 2);
+
+		// Unknown ids are a silent no-op (nothing to bill against).
+		graphStore.appendSourceUsage("src_nope", runEntry(1));
+	} finally {
+		fs.rmSync(SOURCES_FILE, { force: true });
+		if (bak) fs.renameSync(bak, SOURCES_FILE);
+	}
+});