Pin session decisions, questions, objections, scope constraints, and corrections to a persistent board that survives context compaction. Use PROACTIVELY when: (1) user approves/rejects a recommendation, (2) user asks a clarifying question about a proposal, (3) user states a scope constraint, (4) user corrects a misunderstanding. Also use when user says pin, track this, mark as approved, board, show pins. Auto-invoke without user asking whenever a decision, question, or constraint is detected.