diff --git a/scripts/indexer.mjs b/scripts/indexer.mjs
index b3c28c8..cfbbdb2 100644
--- a/scripts/indexer.mjs
+++ b/scripts/indexer.mjs
@@ -1,4 +1,6 @@
 import { CLAUDE_DIR, CODEX_DIR, openDb, rebuildMemoryFts, trunc, truncJson, extractText, extractContentType, extractMessageIsMeta, filePath, isDir, readLines, fs, path } from './db.mjs';
+import { persist } from './persist.ts';
+import { parse as claudeParse } from './providers/claude.ts';
 
 const PROJECTS_DIR = path.join(CLAUDE_DIR, 'projects');
 const HISTORY_PATH = path.join(CLAUDE_DIR, 'history.jsonl');
@@ -782,7 +784,14 @@ function buildIndex({ force = false } = {}) {
       if (f.source === 'codex') {
         indexCodexJsonl(db, f);
       } else {
-        indexJsonl(db, f);
+        // Claude transcripts now go through the pure adapter + shared persist
+        // (docs/adr/0001). needsReindex keeps the "skip unchanged file" fast path;
+        // the cursor's line count drives incremental resume inside parse().
+        const { needed, skip } = needsReindex(db, f.path);
+        if (needed) {
+          const unit = { key: f.path, sessionId: f.sessionId, project: f.project, isSubagent: f.isSubagent, agentId: f.agentId };
+          persist(db, unit, claudeParse(unit, skip > 0 ? `0:${skip}` : null));
+        }
         indexSubagentMeta(db, f);
       }
       db.exec('COMMIT');
diff --git a/tests/incremental-index.test.mjs b/tests/incremental-index.test.mjs
new file mode 100644
index 0000000..1b03591
--- /dev/null
+++ b/tests/incremental-index.test.mjs
@@ -0,0 +1,70 @@
+// Phase 5b-2b: verifies incremental (resume) indexing through the full rewired
+// buildIndex path (needsReindex → cursor → claude.parse → persist). A force
+// --build re-scans everything (skip=0) and never exercises resume, so this
+// appends new lines to an already-indexed session and drives an incremental
+// build. The 30s shouldSkipBuild debounce is cleared between steps (it would
+// otherwise skip a build this soon after the previous one).
+
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { createRequire } from 'node:module';
+import { mkdtempSync, mkdirSync, writeFileSync, appendFileSync, utimesSync, statSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { spawnSync } from 'node:child_process';
+
+const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..');
+const require = createRequire(import.meta.url);
+const { DatabaseSync } = require('node:sqlite');
+
+function runRuntime(args, home) {
+  return spawnSync(process.execPath, ['scripts/runtime.mjs', ...args], {
+    cwd: repoRoot, env: { ...process.env, HOME: home }, encoding: 'utf8',
+  });
+}
+
+function line(uuid, type, ts) {
+  return JSON.stringify({ uuid, type, timestamp: ts, cwd: '/tmp/proj', message: { role: type, content: `${type} ${uuid}` } });
+}
+
+function clearBuildDebounce(home) {
+  const db = new DatabaseSync(join(home, '.obelisk', 'obelisk.sqlite'));
+  db.prepare("DELETE FROM index_state WHERE jsonl_path='__last_build__'").run();
+  db.close();
+}
+
+function counts(home) {
+  writeFileSync(join(home, 'q.mjs'), "return { mc: sql(\"SELECT message_count FROM sessions WHERE id='sess'\")[0]?.message_count ?? null, n: sql('SELECT COUNT(*) c FROM messages')[0].c, lp: sql(\"SELECT lines_processed lp FROM index_state WHERE jsonl_path LIKE '%sess.jsonl'\")[0]?.lp ?? null };");
+  const r = runRuntime(['--query', join(home, 'q.mjs')], home);
+  assert.equal(r.status, 0, r.stderr || r.stdout);
+  return JSON.parse(r.stdout);
+}
+
+test('incremental buildIndex resumes from cursor and accumulates message_count', () => {
+  const home = mkdtempSync(join(tmpdir(), 'obelisk-incr-'));
+  const projDir = join(home, '.claude', 'projects', '-tmp-proj');
+  mkdirSync(projDir, { recursive: true });
+  const jsonl = join(projDir, 'sess.jsonl');
+
+  writeFileSync(jsonl, [line('u1', 'user', '2026-06-10T10:00:00Z'), line('a1', 'assistant', '2026-06-10T10:00:05Z')].join('\n') + '\n');
+  assert.equal(runRuntime(['--build'], home).status, 0);
+
+  const afterBuild = counts(home);
+  assert.equal(afterBuild.mc, 2, 'full build indexed both messages');
+  assert.equal(afterBuild.n, 2);
+  assert.equal(afterBuild.lp, 2, 'cursor recorded 2 lines processed');
+
+  // Append two messages; bump mtime so needsReindex detects the change.
+  appendFileSync(jsonl, [line('u2', 'user', '2026-06-10T10:01:00Z'), line('a2', 'assistant', '2026-06-10T10:01:05Z')].join('\n') + '\n');
+  const t = statSync(jsonl).mtimeMs / 1000 + 10;
+  utimesSync(jsonl, t, t);
+  clearBuildDebounce(home);
+
+  // Incremental build: resume at line 2, add exactly the two new messages.
+  // mc=4 proves resume+accumulate; 6 would mean re-count from stale base, 2 a miss.
+  const afterAppend = counts(home);
+  assert.equal(afterAppend.mc, 4, 'message_count accumulated to 4');
+  assert.equal(afterAppend.n, 4, 'exactly four messages, no duplicates');
+  assert.equal(afterAppend.lp, 4, 'cursor advanced to 4 lines');
+});