free-recall explain tool: the quizzing-mechanic switch (owner 2026-09-27)

Sycophancy mitigation as a structural commitment: the model writes its
full correctAnswer (plus explanation, in that order) BEFORE the learner
sees the question; the commitment rides the persisted call args, is
revealed on submit, and grades his free text in the model's next reply —
the client never grades free recall.

- tools.explain setting (segmented 'Quizzing — Multiple choice | Free
  recall' in Agent settings' Tools group): free arms explain and drops
  quiz for BOTH agents (prober variant carries no nodeId, same pattern
  as the probe quiz); mechanics keys never pass filterEnabledTools —
  quiz stays unwritable (the 2026-09-19 wedge ruling stands)
- doctrine lives pi-natively in the tool descriptions (owner ruling —
  no conditional system-prompt chunks): explain carries the commitment
  rule; the MC option-building craft moved out of the prompt into the
  quiz description; shared/20-question-tools.md slims to the
  quiz-agnostic core
- display seams: parseExplainInput (LaTeX-debris restoration included),
  dock text-mode with an 'I don't know' row (kbd row 0), AnsweredCard
  reveal (The answer / Why, no verdict chips), [Explain answer] format
- phases/plan seams recognize both quizzing tools' nodeId tags; explain
  answers deliberately feed no ledger evidence (no client grading to
  key on — a future ruling can parse the model's grade)

1049/1049 tests, typecheck/lint/build green.

src/agent/teacher-agent.ts

@@ -203,7 +203,8 @@ function baseAgentOptions(kind: AgentKind, opts: AgentBuildOptions, tools: Agent
 }
 
 /**
- * The PROBER (agent A): quiz (no nodeId) + ask + probe_done, lean on
+ * The PROBER (agent A): the quizzing tool (quiz, or explain under free
+ * recall — no nodeId either way) + ask + probe_done, lean on
  * probing doctrine. Its whole job is bracketing the learner's edge and
  * concluding with the assessment (probe_done) — which also queues the
  * handoff wake (see tools/probe.ts) and is the transcript seam the