feat(agents): W2/S1 plugin split — probe (sonnet) + advisor reasoner (opus) + plugin-gate include (BDR-077)

plugin-advisor keeps its name, becomes the opus REASONER: PHASE 1 bash
extracted to new plugin-probe (sonnet, facts-only PROBE REPORT), PHASE 4
apply + checkpoint hoisted to new lib/plugin-gate.md (main-loop include,
doc-commit.md x6 pattern). Fail-closed: advisor ERRORs on missing report.
4 consumers rewired (plugin-check, onboard, init-project, ship-feature).
In-wave planted-input smoke PASSED: probe report complete w/ fallbacks;
advisor consumed every planted field (monorepo per-package note, fast-libs
ctx7 reco) with zero re-detection; ERROR verdict on absent report.
Census §13 (81 pass). Note: new subagent_type registers next session —
resolution re-check before wave merge.

skills/onboard/SKILL.md

@@ -21,7 +21,7 @@ $ARGUMENTS
 
 ## STEP 0 — PLUGIN CHECK + AUTO-ACTIVATE
 
-Load `$HOME/.claude/agents/plugin-advisor.md` with hint "onboarding existing project + $ARGUMENTS".
+Run `$HOME/.claude/lib/plugin-gate.md` with hint "onboarding existing project + $ARGUMENTS" (dispatch plugin-probe → checkpoint → dispatch plugin-advisor → gates in this loop, BDR-077).
 
 - ACTION REQUIRED → show RECOMMENDATIONS block, offer: A) apply recos B) type "force". STOP.
 - PROPOSED CHANGES exist → show list, ask "Apply? (yes / no / customize)". Apply on confirm.