feat(skills): add 3-way adversarial plan-challenge phase to reflection orchestrators

After a plan/reflection is elaborated and before it executes, three fresh blind
sub-agents (correctness / robustness / simplicity) attack it on the big model;
the main loop RE-THINKS every aspect a BLOCKER lands (a named plan change, or
[deferred]) and re-challenges once if the plan materially changed. Advisory into
each skill's existing human gate — the human stays the decider.

- lib/challenge-plan.md — reusable phase: fail-safe (never fail open),
  severity-driven (any single-lens BLOCKER = must-address), RE-THINK loop
- agents/plan-challenger.md — challenger role (read-only, big-model per BDR-066)
- lib/tests/plan-challenger.test.sh — 41-assertion structure lock
- wired into 11 orchestrators: ship-feature/init-project/feat/bugfix (build-plan),
  onboard/audit-delta/code-clean (proposals), seo/geo/harden/web-validate (fix-bundle)

Hardened by dogfooding: 3 blind challengers reviewed this feature's own v1 plan
and caught 4 BLOCKERs (fail-open, consensus-buries-lone-finding, wrong model
tier vs BDR-066, false on-disk-plan premise) — all fixed here.

lib/challenge-plan.md

@@ -0,0 +1,85 @@
+# Challenge the plan — shared orchestrator include
+
+Runs in the ORCHESTRATOR MAIN LOOP after a plan / reflection is elaborated and
+BEFORE it is executed. Turns a fresh plan into a hardened one by attacking it
+from three independent angles, then RE-THINKING every aspect a challenger lands.
+Loop + synthesis decisions live here, in the main loop (BDR-066: reflection runs
+on the big model; `verify-secure-loop.md`: fresh blind gates, decisions in the
+loop). It never merges, executes, or edits code — it hardens the plan and hands
+it to the orchestrator's existing human gate.
+
+The challenge is ADVISORY into that gate — no new hard block — but a BLOCKER is
+never silently carried past: it is either closed by a NAMED plan change or
+explicitly deferred for the human.
+
+## Inputs the caller must have ready
+
+- `PLAN`: path to the plan ON DISK. If your plan is still inline (a printed
+  checklist / diagnosis / fix plan), FIRST persist it to
+  `.claude/tasks/plans/<date>-<slug>-<HHMM>.md` — the challengers read from disk
+  and judge blind, exactly like the verifier reads the contract.
+- `KIND`: `build-plan` | `proposals` | `fix-bundle` — tunes the lens framing
+  below; the mechanism is identical.
+- `SCOPE`: the files/dirs the plan touches (grounds the critique).
+- `CONSTRAINTS` (optional): the decided trade-offs / rejected alternatives from
+  the design step, so a lens does not re-litigate a settled choice.
+
+Nominal path is cheap for a small, clean plan: three parallel challengers return
+SOLID, synthesis is a no-op. It only costs more when a lens lands a real finding
+— which is the point.
+
+## DISPATCH — three fresh challengers, in parallel, blind
+
+Dispatch THREE fresh `plan-challenger` subagents IN PARALLEL, one per LENS, each
+blind to the others and to this conversation:
+
+```
+Agent(subagent_type="plan-challenger", description="challenge:<lens>", prompt="""
+  PLAN: <the PLAN path>
+  LENS: <correctness | robustness | simplicity>   # one per agent — all three
+  SCOPE: <SCOPE>
+  CONSTRAINTS: <CONSTRAINTS, if any>
+""")
+```
+
+**MODEL (BDR-066):** plan critique is AUDIT JUDGMENT — do NOT pin
+`model: "sonnet"`; the challengers inherit the big session model. (The executor
+gates stay sonnet; the challenger does not.)
+
+**Lens framing by `KIND`** (the agent's three lenses, read against the artifact):
+- `build-plan` — will it WORK / will it BREAK / is it needlessly COMPLEX.
+- `proposals` — are these the RIGHT items & priorities / what did the audit MISS
+  or under-rate as risk / is the backlog over- or under-scoped.
+- `fix-bundle` — will each fix ACHIEVE its goal / could it BREAK or regress the
+  page / is there a simpler fix, or an unnecessary one.
+
+## FAIL-SAFE — never fail open
+
+A challenger that returns a malformed/empty verdict, a missing `PROOF`, or dies →
+retry ONCE with a fresh challenger; a 2nd failure on that lens → STOP and escalate
+to the human, NAMING the lens. Never carry "plan challenged" into the gate on a
+silently dropped lens (`verify-secure-loop.md`: "a mute verifier is NEVER a PASS").
+
+## SYNTHESIZE + RE-THINK (main loop, big model)
+
+Parse each `CHALLENGE — LENS: … — VERDICT:` line and merge the FINDINGS:
+
+- **Severity-driven, not consensus.** Any `[BLOCKER]` from ANY single lens is
+  must-address — the lenses are orthogonal, so a lone security/rollback finding
+  is real, never outvoted by lens-count. Cross-lens agreement only RANKS the MINORs.
+- **RE-THINK the aspect the challenge pointed at.** For each BLOCKER (and each
+  MAJOR you accept): revise the plan on THAT aspect — a NAMED, diffable change to
+  the plan, never a self-authored "addressed" line. A BLOCKER you consciously keep
+  is tagged `[deferred <date>]` for the human to accept at the gate.
+- **Re-challenge once if the plan materially changed** — a fix can open a new
+  flaw. Re-persist the revised `PLAN`, dispatch ONE fresh confirmation challenger,
+  max 1 extra pass, then the gate.
+
+## OUTPUT — into the existing human gate
+
+Feed the orchestrator's gate:
+- the REVISED plan, and
+- a CHALLENGE SUMMARY: each BLOCKER raised → the named change that closed it;
+  anything `[deferred]`; and any lens that failed to return.
+
+The human remains the decider.