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.

lib/plugin-gate.md

@@ -0,0 +1,90 @@
+# Plugin gate — shared consumer include (plugin-check, onboard, init-project, ship-feature STEP 0)
+
+Runs in the CONSUMER'S MAIN LOOP. The detection and the reasoning are
+dispatched (BDR-077 tiers); the validation checkpoint, the report
+presentation, and the apply gate live HERE — a dispatched agent can neither
+ask the user nor safely mutate plugin state.
+
+## 1. PROBE (dispatch — sonnet)
+
+```
+Agent(subagent_type="plugin-probe", description="plugin gate — probe",
+      prompt="Run your probes from <PROJECT_ROOT>. Emit the PROBE REPORT.")
+```
+
+## 2. VALIDATION CHECKPOINT (main loop — between probe and reasoner)
+
+Validate the PROBE REPORT before any reasoning:
+- `EXTERNAL` non-empty AND each listed plugin's directory appears under
+  `CHECKPOINT plugin-dirs`.
+- At least one project signal present (MANIFESTS / FRAMEWORK-DEPS /
+  TSX-JSX-COUNT > 0 / DOCKER-COUNT > 0 / EMBEDDED hits). Else print
+  `⚠️ No project signals detected — recommendations will be conservative.`
+  and continue.
+- `CHECKPOINT toggle-script=UNAVAILABLE` → print `⚠️ toggle script
+  unavailable — recommendations will be advisory only, no auto-activation.`
+  and SKIP step 5 (apply) entirely.
+- PROBE REPORT missing/unparsable → retry the probe ONCE fresh; a 2nd
+  failure → STOP and surface (never reason over invented detection).
+
+## 3. REASON (dispatch — opus)
+
+```
+Agent(subagent_type="plugin-advisor", description="plugin gate — reason",
+      prompt="""
+REQUEST: <the user's request / project description, verbatim>
+PROBE REPORT (ground truth — do not re-detect):
+<the full PROBE REPORT from step 1>
+""")
+```
+
+## 4. PRESENT + BLOCKING GATE (main loop)
+
+Show the returned PLUGIN CHECK block.
+- `ACTION REQUIRED? YES` → offer: A) fix plugins B) type "force". STOP until
+  answered.
+- OK → print `✅ Plugin check passed — [active plugins] — complexity: <score>%`.
+
+## 5. APPLY GATE (main loop — only when the flow auto-activates)
+
+If any plugin has ⚡ ENABLE status:
+1. List the changes:
+   ```
+   PROPOSED CHANGES:
+     ⚡ Enable ui-ux-pro-max (frontend detected, complexity 65%)
+     ⚡ Pre-fetch ctx7 docs for next.js, prisma
+   Apply these changes? (yes / no / customize)
+   ```
+2. "yes" → apply via the exact commands the advisor emitted. "customize" →
+   user picks. "no" → proceed with current config.
+
+**Never auto-activate without showing the list and getting confirmation.**
+
+### Rollback on partial failure
+
+Track each toggle; roll back the partial set rather than leave a
+half-applied configuration:
+
+```bash
+applied=()
+for change in "${PROPOSED_CHANGES[@]}"; do
+  if bash "$HOME/.claude/lib/toggle-external.sh" enable "$change"; then
+    applied+=("$change")
+  else
+    echo "❌ failed to enable $change — rolling back ${#applied[@]} prior change(s)"
+    for prior in "${applied[@]}"; do
+      bash "$HOME/.claude/lib/toggle-external.sh" disable "$prior" \
+        || echo "⚠️ rollback of $prior also failed — manual cleanup required: see ~/.claude/plugins/cache"
+    done
+    exit 1
+  fi
+done
+```
+
+Surface: `✅ Applied N change(s).` — or on failure:
+
+```
+⚠️ Toggle failed at change <name>. Rolled back the N prior change(s).
+   To inspect manually: ls ~/.claude/plugins/cache; bash ~/.claude/lib/toggle-external.sh list
+   Re-run /plugin-check after fixing the underlying cause (e.g. permissions).
+```