STALE mode + domain-volatility classifier

[tomas-samek]

Summary

STALE mode exists in the enum but is never triggered. It needs a domain-volatility classifier: some domains (weather, prices, news) decay fast; others (math, history) do not.

What to do

• Design a lightweight volatility classifier. Options:
  • Per-layer domain tag carries a volatility hint set at layer_begin.
  • Inferred from concept churn / update frequency.
  • Explicit per-memory volatility field at deposit time.
• Wire into the cascade: memories older than recency_threshold(volatility) → STALE mode.
• Renderer template for STALE surfaces "this may be outdated" language.

Acceptance

• STALE mode fires on an obviously-stale volatile memory.
• Does not fire on stable-domain memories regardless of age.

Links

• docs/design/honest_agent/progress.md Phase D.
• src/mcp/responder.rs (cascade).