feat(gateguard): improve first-touch signal quality and session efficiency

- Ask class-specific first-touch questions (instruction, test, prose,
  config, code); code questions are unchanged.
- Credit a completed Glob/Grep/LS or shell search from the current human
  turn that covered the target; Read and exclusion globs never count.
- Collapse same-class new-file creations in one directory within a turn.
- Add opt-in GATEGUARD_FACT_FORCE_MAX_DENIALS session cap (from #2755).
- Always gate sensitive targets, judged on lexical and real paths.
- Canonicalize checked-path keys.

Closes #2608

Co-authored-by: SulimanAbdulrazzaq <suliman9000a@gmail.com>

tests/lib/transcript-context.test.js

@@ -18,6 +18,8 @@ const {
   DEFAULT_CONTEXT_THRESHOLD_STANDARD,
   DEFAULT_CONTEXT_THRESHOLD_LARGE,
   DEFAULT_CONTEXT_INTERVAL_TOKENS,
+  DEFAULT_TRANSCRIPT_TAIL_BYTES,
+  readFileTail,
   readLatestContextTokens,
   resolveContextWindowTokens,
   resolveContextThreshold,
@@ -323,6 +325,20 @@ test('returns -1 for non-finite token counts', () => {
   assert.strictEqual(computeContextBucket(NaN, 160000, 60000), -1);
 });
 
+// ── readFileTail ──
+console.log('\nreadFileTail:');
+
+test('is exported and returns the trailing bytes with a truncation flag', () => {
+  assert.strictEqual(typeof readFileTail, 'function');
+  assert.strictEqual(DEFAULT_TRANSCRIPT_TAIL_BYTES, 256 * 1024);
+  const file = tracked(writeTranscript(['first-line', 'second', 'third']));
+  const whole = readFileTail(file, 1024);
+  assert.deepStrictEqual(whole, { text: 'first-line\nsecond\nthird\n', truncated: false });
+  const tail = readFileTail(file, 6);
+  assert.deepStrictEqual(tail, { text: 'third\n', truncated: true });
+  assert.strictEqual(readFileTail(path.join(os.tmpdir(), `missing-${process.pid}.jsonl`), 10), null);
+});
+
 // ── formatWindowLabel ──
 console.log('\nformatWindowLabel:');