fix(voyage): S23 — make /trekplan Phase 9 dedup executable (defect #1)

Phase 9's dedup hand-off was broken on two layers, both surfaced by the S22
dogfood: (a) plan-critic + scope-guardian (Read/Glob/Grep, no Write) were told
to write /tmp/*-out.json the dedup helper reads — they cannot; (b) even with
Write, their Output format emits markdown, not the helper's
{agent,findings:[{file,line,rule_key,text}]} schema. readJsonOrNull then
swallowed the absent files -> a silent empty merge that discarded every finding.

Fix (operator-chosen A'): keep the reviewers read-only; make the hand-off run.
- plan-review-dedup.mjs gains a --stdin mode reading {plan_critic,scope_guardian};
  malformed stdin exits non-zero so a broken hand-off surfaces loudly instead of
  collapsing into a silent empty merge. File mode + its tests are untouched.
- plan-critic.md + scope-guardian.md now emit a trailing machine-readable `json`
  findings block (the inline hand-off; no Write tool needed).
- trekplan.md + planning-orchestrator.md Phase 9 rewritten in lockstep: extract
  both blocks, pipe via heredoc into --stdin. No temp files, portable, no
  pathguard dependency.

TDD: malformed-stdin test failed first (CLI ignored stdin -> exit 0 = the bug),
green after impl. New S23 doc-pin asserts both docs use --stdin (not the dead
/tmp paths) and both agents declare the json block. Suite 724 (722/2/0); live
HEAD baseline was 720, not the stale 705 STATE carried forward.

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

agents/planning-orchestrator.md

@@ -417,16 +417,21 @@ have zero data dependencies; serializing them wastes 30–60 seconds per run.
   missing error handling, scope creep, underspecified steps, AND manifest
   quality (dimension 10: every step has a valid, regex-compilable,
   path-verified manifest). Missing or invalid manifest = **major** finding.
-  Write structured JSON to `/tmp/plan-critic-out.json`.
+  Returns its findings as a trailing machine-readable `json` block (it has no
+  Write tool — the block is the hand-off).
 - `scope-guardian` — verify plan matches the brief's requirements, find scope
   creep (plan does more than the brief specifies) and scope gaps (plan misses
   brief requirements), validate file/function references. Confirm every
   Success Criterion in the brief is covered by the plan's Verification section.
-  Write structured JSON to `/tmp/scope-guardian-out.json`.
+  Returns its findings as a trailing machine-readable `json` block (no Write tool).
 
-After both complete, run an inline dedup pass via
-`node ${CLAUDE_PLUGIN_ROOT}/lib/review/plan-review-dedup.mjs --plan-critic /tmp/plan-critic-out.json --scope-guardian /tmp/scope-guardian-out.json > /tmp/plan-review-merged.json`.
-The merged array attributes each finding to `[plan-critic, scope-guardian]`
+After both complete, extract each reviewer's trailing `json` findings block and
+pipe both into the dedup helper via **stdin** (the reviewers are read-only and
+cannot write temp files; the orchestrator persists by piping their inline blocks):
+`node ${CLAUDE_PLUGIN_ROOT}/lib/review/plan-review-dedup.mjs --stdin` fed
+`{ "plan_critic": <block>, "scope_guardian": <block> }`. The helper exits
+non-zero on malformed stdin, so a broken hand-off cannot hide behind an empty
+merge. The merged array attributes each finding to `[plan-critic, scope-guardian]`
 if both reviewers raised it. Revise the plan once for the merged set, not
 twice for the duplicates. Source: research/05 R1 + R2.