fix(overseer): decouple meta-thread health from isolated act() errors (#4080)

[rysweet]

Problem (#4080)

The primary overseer meta-thread reported erroring at its last tick even though it was still intervening normally. Root cause: the daemon derived the meta-thread's last_success from !report.panicked && report.errors == 0, so a single transient per-intervention act() failure — explicitly documented as "isolated, never fatal" — pinned the thread in "erroring", and a later healthy tick never cleared it.

Fix (additive / non-breaking)

• Add cycle_failed: bool to OverseerTickReport, set only when the tick's OODA cycle itself fails (run_cycle() returns Err, or the tick panics — which also sets panicked).
• Daemon now derives meta-thread health from !panicked && !cycle_failed. Isolated act() errors are still counted in errors (feed/totals visibility) but no longer drive health.
• Health is recomputed fresh each tick, so the first clean tick flips erroring → ok automatically — no latched-flag reset needed.
• #[serde(default)] covers the new field: legacy feed records deserialize with cycle_failed = false; no SCHEMA_VERSION bump.
• cycle_failed added to structured tracing + the daemon log line for observability.

Tests

Regression coverage in src/overseer/wiring.rs and src/overseer/activity.rs:

• isolated act() error → cycle_failed = false → meta-thread stays ok (the erroring→ok recovery path)
• run_cycle() Err → cycle_failed = true → erroring
• panic → panicked + cycle_failed → erroring
• legacy JSON without the field deserializes to false

Verification

• cargo test --lib overseer — 489 passed
• pre-commit: cargo fmt --check, cargo clippy --release -D warnings — pass
• pre-push: full test suite + cargo clippy --all-targets --all-features -D warnings — pass

Additive / non-breaking; PRD preserved; no Bridge naming; structured tracing + OpenTelemetry only, no stray print!/println!.

Closes #4080

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[github-actions]

📊 Coverage Summary

Generated by cargo llvm-cov --workspace --summary-only (nightly, excluding test files)

Module	Lines	Covered	Coverage
Total	182882	152630	83.5%

_{Coverage data from CI run. Test files matching tests?/ are excluded from line counts.}