diff --git a/CLAUDE.md b/CLAUDE.md
index 37eb44e..8b270d0 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -419,6 +419,22 @@ Same hybrid split as Chunk 2b — a deterministic, byte-stable, unit-tested core
   like `/config-audit optimize`. **No new agent** (web poll runs in the command's own context), **no new
   orchestrated scanner**. suite 1068→1091.
 
+### campaign-ledger — durable machine-wide campaign core (v5.7 Fase 2, Block 3a THIN)
+
+`scanners/lib/campaign-ledger.mjs`: the durable ledger that sits ABOVE individual sessions for a
+machine-wide audit campaign — repo list + per-repo lifecycle (`STATUSES` = pending→audited→planned
+→implemented) + a machine-wide `rollUp` (counts by status + severity aggregated across repos). It
+persists to a single JSON file **outside** the plugin dir (`~/.claude/config-audit/campaign-ledger
+.json`, next to `sessions/`) so it survives uninstall/reinstall/upgrade. Same hybrid split as
+knowledge-refresh: PURE transforms (`createLedger`/`addRepo`/`setRepoStatus`/`rollUp`) with `now`
+**injected** (YYYY-MM-DD, never the clock) + soft `validateLedger` (returns `{valid,errors}`, never
+throws) + a thin IO shell (`defaultLedgerPath`/`loadLedger`→null-on-ENOENT/`saveLedger`). Transforms
+throw on programmer error (invalid status, unknown path); `schemaVersion` stamped from the start so a
+Block 4 migration is cheap. **THIN**: ledger + roll-up + persistence only — NO execution, CLI, or
+command surface (Blocks 3b/3c/4). **Internal plumbing, byte-stable until consumed**: no `export async
+function scan` + lives in `lib/` → scanner count stays 15, no orchestrator wiring, SC-5 unchanged.
+28 tests, suite 1091→1119.
+
 ## Gotchas
 
 - Session directories accumulate — use `/config-audit cleanup` to manage
diff --git a/scanners/lib/campaign-ledger.mjs b/scanners/lib/campaign-ledger.mjs
new file mode 100644
index 0000000..e8a47c9
--- /dev/null
+++ b/scanners/lib/campaign-ledger.mjs
@@ -0,0 +1,222 @@
+/**
+ * campaign-ledger — durable, machine-wide campaign ledger (v5.7 Fase 2, Block 3a THIN).
+ *
+ * The ledger sits ABOVE individual config-audit sessions: it tracks which repos are part
+ * of a machine-wide audit campaign, each repo's lifecycle status (pending → audited →
+ * planned → implemented), and a machine-wide roll-up by status + severity. It is resumable
+ * across sessions because it persists to a single JSON file OUTSIDE the plugin dir
+ * (`~/.claude/config-audit/campaign-ledger.json`, next to `sessions/` and `mcp-cache/`),
+ * so it survives plugin uninstall/reinstall/upgrade.
+ *
+ * Design mirrors the knowledge-refresh precedent: the transformations are PURE and
+ * deterministic (every "now" is injected as a YYYY-MM-DD string, never read from the clock
+ * here), so they are fully unit-testable; a thin IO shell (load/save, explicit path) does
+ * the only filesystem work. `validateLedger` is soft (returns a result, never throws) for
+ * externally-loaded data; the transforms throw on programmer error (invalid status, unknown
+ * path). `schemaVersion` is stamped from the start so a future Block 4 migration is cheap.
+ *
+ * THIN scope (Block 3a): ledger core + roll-up + persistence only — NOT execution,
+ * orchestration, or a command surface (those are Blocks 3b/3c/4). Zero dependencies.
+ * See docs/v5.7-optimization-lens-plan.md §Fase 2.
+ */
+
+import { readFile, writeFile, mkdir } from 'node:fs/promises';
+import { dirname, join, resolve } from 'node:path';
+import { homedir } from 'node:os';
+
+/** Ledger schema version — bump + add a migration (Block 4) on any breaking shape change. */
+export const CAMPAIGN_SCHEMA_VERSION = 1;
+
+/** Per-repo lifecycle, in order. A repo advances through these as the campaign progresses. */
+export const STATUSES = Object.freeze(['pending', 'audited', 'planned', 'implemented']);
+
+/** Severity buckets aggregated by the machine-wide roll-up. */
+const SEVERITIES = Object.freeze(['critical', 'high', 'medium', 'low']);
+
+const DATE_RE = /^\d{4}-\d{2}-\d{2}$/;
+
+/** Validate an injected `now` (required, YYYY-MM-DD). Throws — callers pass today's date. */
+function requireNow(now) {
+  if (typeof now !== 'string' || !DATE_RE.test(now)) {
+    throw new TypeError('now must be a YYYY-MM-DD string');
+  }
+  return now;
+}
+
+/** Canonicalize a repo path so the same repo never appears twice under different spellings. */
+function normalizePath(path) {
+  if (typeof path !== 'string' || path.trim() === '') {
+    throw new TypeError('repo path is required');
+  }
+  return resolve(path);
+}
+
+/**
+ * Build an empty, versioned ledger stamped with `now`.
+ * @param {{now: string}} opts
+ * @returns {{schemaVersion:number, createdDate:string, updatedDate:string, repos:object[]}}
+ */
+export function createLedger({ now } = {}) {
+  requireNow(now);
+  return { schemaVersion: CAMPAIGN_SCHEMA_VERSION, createdDate: now, updatedDate: now, repos: [] };
+}
+
+/**
+ * Add a repo to the campaign (status `pending`). Idempotent on the normalized path — a repo
+ * already present is left untouched (its progress is NOT reset). Returns a NEW ledger.
+ * @param {object} ledger
+ * @param {{path: string, name?: string}} repo
+ * @param {{now: string}} opts
+ */
+export function addRepo(ledger, { path, name } = {}, { now } = {}) {
+  requireNow(now);
+  const resolved = normalizePath(path);
+  if (ledger.repos.some((r) => r.path === resolved)) {
+    return ledger; // idempotent: already tracked, preserve its status
+  }
+  const repo = {
+    path: resolved,
+    name: typeof name === 'string' && name.trim() !== '' ? name : resolved.split('/').pop(),
+    status: 'pending',
+    sessionId: null,
+    findingsBySeverity: null,
+    updatedDate: now,
+  };
+  return { ...ledger, updatedDate: now, repos: [...ledger.repos, repo] };
+}
+
+/**
+ * Transition a tracked repo to a new status, optionally attaching the audit's
+ * findings-by-severity and the producing sessionId. Returns a NEW ledger.
+ * @param {object} ledger
+ * @param {string} path
+ * @param {string} status - one of STATUSES
+ * @param {{now: string, findingsBySeverity?: object|null, sessionId?: string|null}} opts
+ */
+export function setRepoStatus(ledger, path, status, { now, findingsBySeverity, sessionId } = {}) {
+  requireNow(now);
+  if (!STATUSES.includes(status)) {
+    throw new RangeError(`invalid status "${status}" — must be one of ${STATUSES.join(', ')}`);
+  }
+  const resolved = normalizePath(path);
+  const idx = ledger.repos.findIndex((r) => r.path === resolved);
+  if (idx === -1) {
+    throw new Error(`repo "${resolved}" is not in the ledger — addRepo first`);
+  }
+  const updated = { ...ledger.repos[idx], status, updatedDate: now };
+  if (findingsBySeverity !== undefined) updated.findingsBySeverity = findingsBySeverity;
+  if (sessionId !== undefined) updated.sessionId = sessionId;
+  const repos = ledger.repos.slice();
+  repos[idx] = updated;
+  return { ...ledger, updatedDate: now, repos };
+}
+
+/**
+ * Machine-wide roll-up: repo counts by status, plus a severity total aggregated across every
+ * repo that carries `findingsBySeverity`. Pure derivation — never mutates.
+ * @param {object} ledger
+ * @returns {{totalRepos:number, byStatus:object, bySeverity:object, reposWithFindings:number}}
+ */
+export function rollUp(ledger) {
+  const byStatus = Object.fromEntries(STATUSES.map((s) => [s, 0]));
+  const bySeverity = Object.fromEntries(SEVERITIES.map((s) => [s, 0]));
+  let reposWithFindings = 0;
+
+  for (const repo of ledger.repos) {
+    if (byStatus[repo.status] !== undefined) byStatus[repo.status] += 1;
+    const f = repo.findingsBySeverity;
+    if (f && typeof f === 'object') {
+      reposWithFindings += 1;
+      for (const sev of SEVERITIES) {
+        if (typeof f[sev] === 'number') bySeverity[sev] += f[sev];
+      }
+    }
+  }
+  return { totalRepos: ledger.repos.length, byStatus, bySeverity, reposWithFindings };
+}
+
+/**
+ * Validate a parsed ledger against the schema. Never throws — returns every problem at once
+ * so the caller (and tests) can inspect them. Soft by design (loaded data may be corrupt).
+ * @param {unknown} data
+ * @returns {{valid:boolean, errors:string[]}}
+ */
+export function validateLedger(data) {
+  const errors = [];
+  if (!data || typeof data !== 'object' || Array.isArray(data)) {
+    return { valid: false, errors: ['ledger must be an object'] };
+  }
+  if (data.schemaVersion !== CAMPAIGN_SCHEMA_VERSION) {
+    errors.push(`schemaVersion must be ${CAMPAIGN_SCHEMA_VERSION}`);
+  }
+  for (const field of ['createdDate', 'updatedDate']) {
+    if (typeof data[field] !== 'string' || !DATE_RE.test(data[field])) {
+      errors.push(`${field} must be YYYY-MM-DD`);
+    }
+  }
+  if (!Array.isArray(data.repos)) {
+    errors.push('repos must be an array');
+    return { valid: false, errors };
+  }
+
+  const seen = new Set();
+  data.repos.forEach((r, i) => {
+    const at = `repos[${i}]${r && typeof r === 'object' && r.path ? ` (${r.path})` : ''}`;
+    if (!r || typeof r !== 'object' || Array.isArray(r)) {
+      errors.push(`${at}: must be an object`);
+      return;
+    }
+    if (typeof r.path !== 'string' || r.path.trim() === '') {
+      errors.push(`${at}: path is required`);
+    } else if (seen.has(r.path)) {
+      errors.push(`${at}: duplicate path`);
+    } else {
+      seen.add(r.path);
+    }
+    if (!STATUSES.includes(r.status)) {
+      errors.push(`${at}: status must be one of ${STATUSES.join(', ')}`);
+    }
+  });
+
+  return { valid: errors.length === 0, errors };
+}
+
+// ── Persistence (thin IO shell) ────────────────────────────────────────────────
+
+/**
+ * Default on-disk location: next to `sessions/`, OUTSIDE the plugin dir, so the campaign
+ * survives plugin uninstall/reinstall/upgrade.
+ * @returns {string}
+ */
+export function defaultLedgerPath() {
+  return join(homedir(), '.claude', 'config-audit', 'campaign-ledger.json');
+}
+
+/**
+ * Load + parse a ledger file. Returns `null` if the file does not exist (graceful first run);
+ * other read/parse errors propagate so corruption is not silently swallowed.
+ * @param {string} [path]
+ * @returns {Promise<object|null>}
+ */
+export async function loadLedger(path = defaultLedgerPath()) {
+  let content;
+  try {
+    content = await readFile(path, 'utf8');
+  } catch (err) {
+    if (err && err.code === 'ENOENT') return null;
+    throw err;
+  }
+  return JSON.parse(content);
+}
+
+/**
+ * Persist a ledger as human-readable JSON, creating parent directories as needed.
+ * @param {string} path
+ * @param {object} ledger
+ * @returns {Promise<{path: string}>}
+ */
+export async function saveLedger(path = defaultLedgerPath(), ledger) {
+  await mkdir(dirname(path), { recursive: true });
+  await writeFile(path, `${JSON.stringify(ledger, null, 2)}\n`, 'utf8');
+  return { path };
+}
diff --git a/tests/lib/campaign-ledger.test.mjs b/tests/lib/campaign-ledger.test.mjs
new file mode 100644
index 0000000..c1fe43a
--- /dev/null
+++ b/tests/lib/campaign-ledger.test.mjs
@@ -0,0 +1,230 @@
+import { describe, it, after } from 'node:test';
+import assert from 'node:assert/strict';
+import { join } from 'node:path';
+import { mkdtemp, rm, readFile } from 'node:fs/promises';
+import { tmpdir, homedir } from 'node:os';
+import {
+  CAMPAIGN_SCHEMA_VERSION,
+  STATUSES,
+  createLedger,
+  addRepo,
+  setRepoStatus,
+  rollUp,
+  validateLedger,
+  defaultLedgerPath,
+  loadLedger,
+  saveLedger,
+} from '../../scanners/lib/campaign-ledger.mjs';
+
+const NOW = '2026-06-22';
+const LATER = '2026-06-23';
+
+describe('constants', () => {
+  it('schema version is 1', () => {
+    assert.equal(CAMPAIGN_SCHEMA_VERSION, 1);
+  });
+  it('STATUSES is the frozen four-step lifecycle', () => {
+    assert.deepEqual([...STATUSES], ['pending', 'audited', 'planned', 'implemented']);
+    assert.ok(Object.isFrozen(STATUSES));
+  });
+});
+
+describe('createLedger', () => {
+  it('builds an empty, versioned ledger stamped with `now`', () => {
+    const l = createLedger({ now: NOW });
+    assert.deepEqual(l, {
+      schemaVersion: 1,
+      createdDate: NOW,
+      updatedDate: NOW,
+      repos: [],
+    });
+  });
+  it('throws on a missing/invalid now', () => {
+    assert.throws(() => createLedger({}), /now/);
+    assert.throws(() => createLedger({ now: 'June 22' }), /now/);
+  });
+});
+
+describe('addRepo', () => {
+  it('adds a pending repo with name, resolved path, and stamps', () => {
+    const l = addRepo(createLedger({ now: NOW }), { path: '/Users/ktg/repos/foo', name: 'foo' }, { now: NOW });
+    assert.equal(l.repos.length, 1);
+    assert.deepEqual(l.repos[0], {
+      path: '/Users/ktg/repos/foo',
+      name: 'foo',
+      status: 'pending',
+      sessionId: null,
+      findingsBySeverity: null,
+      updatedDate: NOW,
+    });
+  });
+
+  it('normalizes the path (trailing slash, .. segments)', () => {
+    const l = addRepo(createLedger({ now: NOW }), { path: '/Users/ktg/repos/foo/../foo/', name: 'foo' }, { now: NOW });
+    assert.equal(l.repos[0].path, '/Users/ktg/repos/foo');
+  });
+
+  it('is idempotent on path — no duplicate, status preserved', () => {
+    let l = addRepo(createLedger({ now: NOW }), { path: '/r/foo', name: 'foo' }, { now: NOW });
+    l = setRepoStatus(l, '/r/foo', 'audited', { now: NOW });
+    l = addRepo(l, { path: '/r/foo', name: 'foo' }, { now: LATER });
+    assert.equal(l.repos.length, 1);
+    assert.equal(l.repos[0].status, 'audited'); // progress not reset
+  });
+
+  it('bumps ledger.updatedDate but not createdDate', () => {
+    const base = createLedger({ now: NOW });
+    const l = addRepo(base, { path: '/r/foo', name: 'foo' }, { now: LATER });
+    assert.equal(l.createdDate, NOW);
+    assert.equal(l.updatedDate, LATER);
+  });
+
+  it('does not mutate the input ledger', () => {
+    const base = createLedger({ now: NOW });
+    addRepo(base, { path: '/r/foo', name: 'foo' }, { now: NOW });
+    assert.equal(base.repos.length, 0);
+  });
+
+  it('throws on a missing path', () => {
+    assert.throws(() => addRepo(createLedger({ now: NOW }), { name: 'foo' }, { now: NOW }), /path/);
+  });
+});
+
+describe('setRepoStatus', () => {
+  const seed = () => addRepo(createLedger({ now: NOW }), { path: '/r/foo', name: 'foo' }, { now: NOW });
+
+  it('updates status and stamps the repo + ledger', () => {
+    const l = setRepoStatus(seed(), '/r/foo', 'audited', { now: LATER });
+    assert.equal(l.repos[0].status, 'audited');
+    assert.equal(l.repos[0].updatedDate, LATER);
+    assert.equal(l.updatedDate, LATER);
+  });
+
+  it('attaches findingsBySeverity and sessionId when provided', () => {
+    const findings = { critical: 0, high: 2, medium: 5, low: 3 };
+    const l = setRepoStatus(seed(), '/r/foo', 'audited', { now: NOW, findingsBySeverity: findings, sessionId: '20260404_162210' });
+    assert.deepEqual(l.repos[0].findingsBySeverity, findings);
+    assert.equal(l.repos[0].sessionId, '20260404_162210');
+  });
+
+  it('resolves the path the same way addRepo does', () => {
+    const l = setRepoStatus(seed(), '/r/foo/', 'planned', { now: NOW });
+    assert.equal(l.repos[0].status, 'planned');
+  });
+
+  it('throws on an invalid status', () => {
+    assert.throws(() => setRepoStatus(seed(), '/r/foo', 'done', { now: NOW }), /status/);
+  });
+
+  it('throws on an unknown path', () => {
+    assert.throws(() => setRepoStatus(seed(), '/r/bar', 'audited', { now: NOW }), /not in the ledger|unknown/i);
+  });
+
+  it('does not mutate the input ledger', () => {
+    const l = seed();
+    setRepoStatus(l, '/r/foo', 'audited', { now: NOW });
+    assert.equal(l.repos[0].status, 'pending');
+  });
+});
+
+describe('rollUp', () => {
+  it('returns all-zero buckets for an empty ledger', () => {
+    const r = rollUp(createLedger({ now: NOW }));
+    assert.equal(r.totalRepos, 0);
+    assert.deepEqual(r.byStatus, { pending: 0, audited: 0, planned: 0, implemented: 0 });
+    assert.deepEqual(r.bySeverity, { critical: 0, high: 0, medium: 0, low: 0 });
+    assert.equal(r.reposWithFindings, 0);
+  });
+
+  it('counts statuses and aggregates severity machine-wide', () => {
+    let l = createLedger({ now: NOW });
+    l = addRepo(l, { path: '/r/a', name: 'a' }, { now: NOW });
+    l = addRepo(l, { path: '/r/b', name: 'b' }, { now: NOW });
+    l = addRepo(l, { path: '/r/c', name: 'c' }, { now: NOW });
+    l = setRepoStatus(l, '/r/a', 'audited', { now: NOW, findingsBySeverity: { critical: 1, high: 2, medium: 0, low: 4 } });
+    l = setRepoStatus(l, '/r/b', 'implemented', { now: NOW, findingsBySeverity: { critical: 0, high: 1, medium: 3, low: 0 } });
+    // c stays pending, no findings
+
+    const r = rollUp(l);
+    assert.equal(r.totalRepos, 3);
+    assert.deepEqual(r.byStatus, { pending: 1, audited: 1, planned: 0, implemented: 1 });
+    assert.deepEqual(r.bySeverity, { critical: 1, high: 3, medium: 3, low: 4 });
+    assert.equal(r.reposWithFindings, 2);
+  });
+});
+
+describe('validateLedger', () => {
+  const good = () => setRepoStatus(
+    addRepo(createLedger({ now: NOW }), { path: '/r/foo', name: 'foo' }, { now: NOW }),
+    '/r/foo', 'audited', { now: NOW, findingsBySeverity: { critical: 0, high: 0, medium: 1, low: 0 } },
+  );
+
+  it('accepts a well-formed ledger', () => {
+    const res = validateLedger(good());
+    assert.equal(res.valid, true, res.errors.join('; '));
+    assert.deepEqual(res.errors, []);
+  });
+
+  it('rejects a non-object', () => {
+    assert.equal(validateLedger(null).valid, false);
+    assert.equal(validateLedger([]).valid, false);
+  });
+
+  it('rejects a bad schemaVersion', () => {
+    const l = { ...good(), schemaVersion: '1' };
+    assert.equal(validateLedger(l).valid, false);
+  });
+
+  it('rejects repos that is not an array', () => {
+    const l = { ...good(), repos: {} };
+    assert.equal(validateLedger(l).valid, false);
+  });
+
+  it('rejects a repo missing a path', () => {
+    const l = good();
+    l.repos = [{ ...l.repos[0], path: undefined }];
+    assert.equal(validateLedger(l).valid, false);
+  });
+
+  it('rejects a repo with an out-of-enum status', () => {
+    const l = good();
+    l.repos = [{ ...l.repos[0], status: 'done' }];
+    assert.equal(validateLedger(l).valid, false);
+  });
+
+  it('rejects duplicate repo paths', () => {
+    const l = good();
+    l.repos = [l.repos[0], { ...l.repos[0] }];
+    assert.equal(validateLedger(l).valid, false);
+  });
+});
+
+describe('persistence (IO)', () => {
+  it('defaultLedgerPath lives under ~/.claude/config-audit (survives uninstall)', () => {
+    const p = defaultLedgerPath();
+    assert.equal(p, join(homedir(), '.claude', 'config-audit', 'campaign-ledger.json'));
+  });
+
+  it('round-trips through save/load and creates parent dirs', async () => {
+    const dir = await mkdtemp(join(tmpdir(), 'ca-ledger-'));
+    after(() => rm(dir, { recursive: true, force: true }));
+    const file = join(dir, 'nested', 'campaign-ledger.json');
+    const l = good();
+    function good() {
+      return addRepo(createLedger({ now: NOW }), { path: '/r/foo', name: 'foo' }, { now: NOW });
+    }
+    await saveLedger(file, l);
+    const loaded = await loadLedger(file);
+    assert.deepEqual(loaded, l);
+    // human-readable JSON on disk
+    const raw = await readFile(file, 'utf8');
+    assert.match(raw, /\n/);
+  });
+
+  it('loadLedger returns null for a missing file (graceful first run)', async () => {
+    const dir = await mkdtemp(join(tmpdir(), 'ca-ledger-'));
+    after(() => rm(dir, { recursive: true, force: true }));
+    const loaded = await loadLedger(join(dir, 'nope.json'));
+    assert.equal(loaded, null);
+  });
+});