feat(agent): cross-cycle volatility gauge for incident dedup + change awareness

[atomicdragonranch]

Closes #77.

Problem

The coordinator is stateless between cycles and never read its own history, so a persistent anomaly (latency stays bad for N cycles) was re-diagnosed and re-escalated every cycle (alert spam), and every sighting was treated as the first.

Fix

A lightweight in-memory cross-cycle memory on the coordinator instance (which lives for the whole run loop). New VolatilityGauge (agent/volatility.py):

• fingerprints each anomaly as anomaly_type:component (idempotent dedup key);
• classifies a detection as NEW / ONGOING / WORSENING against history, and marks other previously-active incidents RESOLVED;
• WORSENING when observed_value rose by >= agent_incident_worsen_pct since last cycle; ONGOING recurrence within agent_incident_ongoing_gap cycles, else NEW;
• should_report: NEW/WORSENING always; ONGOING only until reported once (agent_incident_dedup), then suppressed;
• prior_context() feeds a "since last cycle" summary into the next detection, so an ongoing anomaly is recognized as such (change awareness).

run_cycle now stamps a cycle number, observes each detection, injects prior context into detection, suppresses a reported unchanged ongoing incident before the expensive diagnose/report, marks reported after escalation, and logs resolved incidents on all-clear. Thresholds externalized to config, validated at startup.

State is in-memory (resets on restart), an accepted tradeoff, durable history already lives in the audit log.

Tests

11 gauge unit tests (fingerprint, new/ongoing/worsening/gap, suppression, not-yet-reported-still-reports, resolved, prior_context, all-clear, dedup-off); a run_cycle two-cycle integration test proving a persistent incident reports once and is suppressed the second cycle; config defaults + validation.

Full suite 273 passed; ruff + mypy clean.

Pairs with #67 (parallel diagnosis): together the coordinator now has cross-cycle and cross-hypothesis intelligence.

https://claude.ai/code/session_01R5VygSzbGTggW7mHd3PVwE