kernel: agenda coherence — stale private threads outrank the live operator thread

[webdevtodayjason]

Self-reported by Argent (gpt-5.5) and verified against kernel state on 2026-06-10:

• agenda.updatedAt: 2026-05-27 — frozen for two weeks, still carrying 'f(S) Bound Derivation' / 'Silver threshold modulation' while activeWork.updatedAt tracks the live conversation correctly.
• Mixed state in one record: activeWork.threadTitle = the live operator thread (memory-retrieval debugging) but activeWork.nextStep = 'Compute discriminant D >= 0 condition' (the stale math thread).
• Ledger churn: 16,781 artifact-ledger entries / 134,657 decision-ledger lines (vs 41 actual artifact files) at ~/.argentos/agents/argent/agent/kernel/.

Wanted (per Argent's own prioritization, which matches the evidence):

1. Recency/operator-priority takeover — active operator debugging should preempt stale private agenda items.
2. Stop conditions for private loops — 'searched memory, found 0 relevant traces' must not repeat without new input.
3. Surfaceable results — kernel/background completions produce a summary or an explicit 'no useful result', never silent completion.

Related: #425 (task-board assignment→claim/heartbeat bridge — item 4 of the same self-report).