diff --git a/plugins/ai-psychosis/hooks/scripts/lib.mjs b/plugins/ai-psychosis/hooks/scripts/lib.mjs
index 4610ff3..a123590 100644
--- a/plugins/ai-psychosis/hooks/scripts/lib.mjs
+++ b/plugins/ai-psychosis/hooks/scripts/lib.mjs
@@ -195,6 +195,37 @@ export function sessionsToday() {
   }
 }
 
+// Tail-first scan: return the N most recent end records (records with
+// duration_min defined) in chronological order. Cost is bounded by N, not
+// by total file size — a 50K-record sessions.jsonl is read once but only
+// the last few hundred lines are JSON-parsed before N is satisfied.
+export function readRecentEndRecords(n) {
+  if (!Number.isFinite(n) || n <= 0) return [];
+  if (!existsSync(SESSIONS_LOG)) return [];
+
+  let lines;
+  try {
+    lines = readFileSync(SESSIONS_LOG, 'utf8').split('\n');
+  } catch {
+    return [];
+  }
+
+  const collected = [];
+  for (let i = lines.length - 1; i >= 0 && collected.length < n; i--) {
+    const line = lines[i];
+    if (!line) continue;
+    try {
+      const rec = JSON.parse(line);
+      if (rec.duration_min !== undefined) {
+        collected.push(rec);
+      }
+    } catch { /* skip malformed */ }
+  }
+
+  // Reverse so caller receives oldest-first (chronological order).
+  return collected.reverse();
+}
+
 // --- State file management ---
 
 export function sessionStateFile(sid) {
diff --git a/plugins/ai-psychosis/tests/lib.test.mjs b/plugins/ai-psychosis/tests/lib.test.mjs
index 0e59fb6..d6843bc 100644
--- a/plugins/ai-psychosis/tests/lib.test.mjs
+++ b/plugins/ai-psychosis/tests/lib.test.mjs
@@ -3,10 +3,19 @@
 // with the expected shape. Detector-level behaviour is covered in
 // per-detector test files (user-info, validation-seeking, stakes-matrix).
 
-import { test, describe } from 'node:test';
+import { test, describe, before, after } from 'node:test';
 import assert from 'node:assert/strict';
+import { mkdtempSync, rmSync, writeFileSync } from 'fs';
+import { join } from 'path';
+import { tmpdir } from 'os';
 
-import {
+// Allocate a fresh data dir before importing lib.mjs, so SESSIONS_LOG points
+// at a sandbox path. The lib.mjs module captures CLAUDE_PLUGIN_DATA at import
+// time, so the env var must be set first.
+const TEST_DATA_DIR = mkdtempSync(join(tmpdir(), 'ia-lib-test-'));
+process.env.CLAUDE_PLUGIN_DATA = TEST_DATA_DIR;
+
+const {
   TIER1_TURN_THRESHOLD,
   TIER2_SESSION_THRESHOLD,
   THRESHOLD_VALSEEK_FLAGS,
@@ -14,7 +23,13 @@ import {
   HIGH_SYCOPHANCY_DOMAINS,
   HIGH_STAKES_DOMAINS,
   INFO_DOMAINS,
-} from '../hooks/scripts/lib.mjs';
+  SESSIONS_LOG,
+  readRecentEndRecords,
+} = await import('../hooks/scripts/lib.mjs');
+
+after(() => {
+  rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
 
 describe('v1.2 thresholds', () => {
   test('tier-1 turn threshold is 15', () => {
@@ -76,3 +91,62 @@ describe('domain classification arrays', () => {
     assert.equal(Object.isFrozen(INFO_DOMAINS), true);
   });
 });
+
+describe('readRecentEndRecords', () => {
+  function writeFixture(records) {
+    const lines = records.map(r => JSON.stringify(r)).join('\n') + '\n';
+    writeFileSync(SESSIONS_LOG, lines);
+  }
+
+  test('returns N most recent end records in chronological order', () => {
+    writeFixture([
+      { session_id: 'a', start: '2026-05-01T10:00:00Z' }, // start record (no duration)
+      { session_id: 'a', start: '2026-05-01T10:00:00Z', end: '2026-05-01T10:30:00Z', duration_min: 30 },
+      { session_id: 'b', start: '2026-05-01T11:00:00Z' },
+      { session_id: 'b', start: '2026-05-01T11:00:00Z', end: '2026-05-01T11:45:00Z', duration_min: 45 },
+      { session_id: 'c', start: '2026-05-01T12:00:00Z', end: '2026-05-01T12:20:00Z', duration_min: 20 },
+      { session_id: 'd', start: '2026-05-01T13:00:00Z', end: '2026-05-01T13:50:00Z', duration_min: 50 },
+    ]);
+
+    const recent = readRecentEndRecords(3);
+    assert.equal(recent.length, 3);
+    assert.equal(recent[0].session_id, 'b');
+    assert.equal(recent[1].session_id, 'c');
+    assert.equal(recent[2].session_id, 'd');
+  });
+
+  test('returns fewer than N when not enough end records exist', () => {
+    writeFixture([
+      { session_id: 'a', start: '2026-05-01T10:00:00Z', end: '2026-05-01T10:30:00Z', duration_min: 30 },
+    ]);
+    const recent = readRecentEndRecords(5);
+    assert.equal(recent.length, 1);
+    assert.equal(recent[0].session_id, 'a');
+  });
+
+  test('skips malformed JSON lines', () => {
+    const goodA = JSON.stringify({ session_id: 'a', duration_min: 1 });
+    const goodB = JSON.stringify({ session_id: 'b', duration_min: 2 });
+    writeFileSync(SESSIONS_LOG, `${goodA}\nnot json\n${goodB}\n`);
+    const recent = readRecentEndRecords(5);
+    assert.equal(recent.length, 2);
+    assert.equal(recent[0].session_id, 'a');
+    assert.equal(recent[1].session_id, 'b');
+  });
+
+  test('empty file returns []', () => {
+    writeFileSync(SESSIONS_LOG, '');
+    assert.deepEqual(readRecentEndRecords(3), []);
+  });
+
+  test('missing file returns []', () => {
+    rmSync(SESSIONS_LOG, { force: true });
+    assert.deepEqual(readRecentEndRecords(3), []);
+  });
+
+  test('non-positive N returns []', () => {
+    writeFixture([{ session_id: 'a', duration_min: 1 }]);
+    assert.deepEqual(readRecentEndRecords(0), []);
+    assert.deepEqual(readRecentEndRecords(-1), []);
+  });
+});