feat(voyage): S18 — framing-hardening (min-version gate + memory status + pre-2.2 doc + flagship hedge)

Closes devils-advocate audit #4–#6 (MAJOR×MED). Four additive, non-breaking
changes to the v5.5 framing-alignment machinery:

1. --min-brief-version <ver> gate (audit #4). Opt-in version floor on
   /trekplan + /trekresearch, forwarded to brief-validator as --min-version.
   New opts.minBriefVersion warns BRIEF_VERSION_BELOW_MINIMUM (never blocks)
   when a brief declares a version below the floor; trekreview exempt; absent
   opt = no check. CLI shim parses --min-version and skips its value token in
   filePath detection.

2. memory_alignment.status field (audit #5). brief-reviewer now emits
   status: verified | n_a | contradictions so a score-5 N/A (no memory) is
   distinguishable from a score-5 verified-aligned brief — the score≥4 gate
   passes in both, status reveals whether the wrong-premise defense ran.

3. Document pre-2.2 = zero framing enforcement (audit #4). HANDOVER-CONTRACTS
   §Handover 1 now states the producer-elective hole + two remedies. Also
   fixes a stale "current is 2.1" line (current is 2.2).

4. Soften flagship overselling (audit #6). CLAUDE.md Context-Engineering
   principle now hedges that main-context relief is asserted-by-design, not
   measured (T1 PoC found Δ≈0); README carried no false claim to fix.

TDD: 8 new tests written failing-first (5 validator, 1 trekbrief status pin,
2 doc-consistency cross-file pins). Suite 691→699 (697 pass / 2 skip / 0 fail).
No flagship prose-pin added (deliberate, per S19 anti-bloat).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LqBYc8Ltrk7LipyJmGxXiB

tests/lib/doc-consistency.test.mjs

@@ -869,3 +869,30 @@ test('S17: NW2 bake-off verdict is not labeled unqualified POSITIVE (raw data un
     'T2-bakeoff-results.md must disclose the raw per-run data is un-archived / un-reproducible.',
   );
 });
+
+// ── S18: framing-hardening cross-file invariants ───────────────────────────
+
+test('S18: --min-brief-version is documented at the trekplan + trekresearch boundary', () => {
+  // The opt-in version floor must be discoverable wherever flags live: both
+  // consuming commands and the central flag reference.
+  for (const f of ['commands/trekplan.md', 'commands/trekresearch.md', 'docs/command-modes.md']) {
+    assert.ok(
+      read(f).includes('--min-brief-version'),
+      `${f} must document the --min-brief-version flag (S18 framing-hardening)`,
+    );
+  }
+});
+
+test('S18: HANDOVER-CONTRACTS documents the pre-2.2 zero-framing-enforcement hole', () => {
+  // The framing defense is producer-elective: a brief declaring ≤ 2.1 sidesteps
+  // it entirely. Handover 1 (PUBLIC CONTRACT) must disclose this and name the remedy.
+  const h = read('docs/HANDOVER-CONTRACTS.md');
+  assert.ok(
+    /BRIEF_VERSION_BELOW_MINIMUM/.test(h),
+    'HANDOVER-CONTRACTS.md must name the BRIEF_VERSION_BELOW_MINIMUM gate as the pre-2.2 remedy',
+  );
+  assert.ok(
+    /zero framing enforcement|no framing enforcement|sidestep/i.test(h),
+    'HANDOVER-CONTRACTS.md must state that pre-2.2 briefs receive zero framing enforcement',
+  );
+});