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

CHANGELOG.md

@@ -13,8 +13,9 @@ The coordinated release held since the framing work. Supersedes the unreleased i
 Three version-gated layers ship at `brief_version ≥ 2.2`, implementing the `CLAUDE.md` cross-cutting invariant "brief framing must match operator intent":
 
 - **`framing` enum** (`preserve | refine | replace | new-direction`) — required in frontmatter, collected in `/trekbrief` Phase 2.5 *before* any prose is written, non-skippable even in `--quick`. Enum-checked on any version (`BRIEF_INVALID_FRAMING`); missing at ≥ 2.2 → `BRIEF_MISSING_FRAMING`.
-- **Memory-alignment dimension** — new `brief-reviewer` dimension 6 compares brief Intent/Goal + framing against operator memory, flagging *explicit* contradictions only (scores N/A when no memory is supplied); wired to the Phase 4e gate (`memory_alignment.score ≥ 4`).
+- **Memory-alignment dimension** — new `brief-reviewer` dimension 6 compares brief Intent/Goal + framing against operator memory, flagging *explicit* contradictions only (scores N/A when no memory is supplied); wired to the Phase 4e gate (`memory_alignment.score ≥ 4`). Emits a `status` field (`verified | n_a | contradictions`) so a score-5 N/A (no memory available) is distinguishable from a score-5 verified-aligned brief — the gate passes in both cases, and `status` is what tells the operator whether the wrong-premise defense actually ran.
 - **Obligatory `## TL;DR`** — ≤ 5 content lines at the top of every 2.2 brief (soft cap → `BRIEF_TLDR_TOO_LONG`).
+- **Opt-in version floor** — `--min-brief-version <ver>` on `/trekplan` + `/trekresearch` (forwarded to the validator as `--min-version`) raises a `BRIEF_VERSION_BELOW_MINIMUM` *warning* — never a block — when a brief declares a version below the floor. Closes the producer-elective hole where a `2.0`/`2.1` brief silently sidesteps framing enforcement; `docs/HANDOVER-CONTRACTS.md` §Handover 1 now documents pre-2.2 = zero framing enforcement and the two remedies (require `2.2` upstream, or pass the floor flag).
 
 Existing `2.0`/`2.1` briefs stay valid (forward + backward compatible), mirroring the `phase_signals ≥ 2.1` precedent. `trekreview` briefs are exempt.