fix(plan): every exploration agent runs; the brief is reviewed again only when it changed

voyage-lekerepo trial (2026-10-06) point 14, operator decision 2026-10-08
(«alle agenter, ny briefsjekk bare ved endring»):

- trekplan: the "Adaptive" hard rule (a 10-file project does not need 7
  agents) contradicted Phase 5 ("All agents run for all codebase sizes");
  it is gone, in line with quality before cost.
- brief-review-stamp.mjs: /trekbrief stamps the brief body when its
  brief-reviewer gate passes; /trekplan Phase 4b skips its own review only
  while the stamp is current. Stale (edited) or absent (another producer,
  or a gate that did not pass) reviews as before. Additive optional
  frontmatter fields, documented in Handover 1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

commands/trekbrief.md

@@ -715,7 +715,13 @@ stumble.)
 1. Move `brief.md.draft` → `brief.md` (atomic rename).
 2. Delete the draft file if rename is not possible on the OS; write
    `brief.md` fresh.
-3. Break the loop and proceed to Step 4g.
+3. Stamp the reviewed body, so `/trekplan` does not run the same review on
+   the same text again (operator decision 2026-10-08):
+   `node ${CLAUDE_PLUGIN_ROOT}/lib/validators/brief-review-stamp.mjs --stamp "{PROJECT_DIR}/brief.md"`.
+   Any later edit to the body makes the stamp stale and `/trekplan` reviews
+   again. Exit 1 (not stamped) is said in one line; it only means the review
+   runs twice. Only a passed gate is stamped.
+4. Break the loop and proceed to Step 4g.
 
 **If gate fails AND iteration count < the class cap:**
 1. Identify the weakest dimension (lowest score; tie broken by priority:

commands/trekplan.md

@@ -429,6 +429,19 @@ Codebase: {N} source files ({scale}). Deploying exploration agents.
 
 ## Phase 4b — Brief review
 
+First check whether `/trekbrief` already reviewed exactly this text:
+
+```bash
+node ${CLAUDE_PLUGIN_ROOT}/lib/validators/brief-review-stamp.mjs --check "{brief_path}"
+```
+
+Exit 0 (`current`): the body is unchanged since `/trekbrief`'s brief-reviewer
+gate passed. Skip the review, say so in one line ("Brief review: skipped —
+unchanged since /trekbrief's review"), and continue to Phase 5. Exit 1
+(`stale`: edited after that review; `absent`: no stamp — a gate that did not
+pass, or a brief from another producer) or 2 (could not run): review it as
+below (operator decision 2026-10-08).
+
 Launch the **brief-reviewer** agent:
 Prompt: "Review this task brief for quality: {brief_path}. Check completeness,
 consistency, testability, scope clarity, and research-plan validity."
@@ -1264,7 +1277,5 @@ Standard and low effort: do NOT emit the section at all.
 - **Honesty**: If exploration reveals the task is trivial (single file, obvious
   change), say so. Do not inflate the plan to justify the process. Suggest
   the user just implements it directly.
-- **Adaptive**: Never spawn more agents than the codebase warrants. A 10-file
-  project does not need 7 exploration agents. Scale down.
 - **Research transparency**: Always distinguish codebase-derived decisions from
   research-derived decisions in the plan.