guest-power: add the liveness observable it shipped without (v0.109.0)

The v0.107.0 watchdog was silent on a healthy box, so its health could only be inferred
from absence — F-OBS's shape, shipped in the same session F-OBS was fixed. INFO summary
every 10th sweep with what it saw; aborted sweeps are not counted. Red-proofs 7 and 8.

CHANGELOG.md

@@ -1,3 +1,30 @@
+## v0.109.0 — the guest-power watchdog gets the observable it was shipped without (2026-07-28)
+
+**Self-correction to v0.107.0, found by running the very check this session added elsewhere.** The new
+guest-power watchdog logged at startup and when it ACTED, and was otherwise silent — so on a healthy
+box the only evidence the sweep was running was the *absence* of start lines. That is exactly F-OBS's
+shape, and exactly what standing rule 3 forbids: an absent log line is not evidence of correct
+behaviour. It shipped in the same session F-OBS was fixed in `deadapp-check`, which is what makes it
+worth recording rather than quietly patching.
+
+`GuestPowerTick` now emits an INFO summary every **10th** sweep (10 x 60 s = 10 min, matching the
+controller's deadapp heartbeat) carrying `sweeps_since_boot`, `guests_evaluated` and
+`currently_stopped`. It reports **what the sweep saw**, not merely that it ran — "alive, all guests up"
+and "alive, one guest deliberately left down" are different operator facts and a bare liveness ping
+cannot express the second.
+
+Two bounds, both pinned by test in the direction that would break them:
+- **Not a flood.** One line per sweep would be 1440/day, which is the pressure that made silence
+  attractive in the first place. A test fails if the cadence degenerates to per-sweep.
+- **An aborted sweep does not count.** If `Guests()` fails, ownership is unproven and the sweep
+  examines nothing; counting it would have the heartbeat claim liveness for a watchdog doing nothing —
+  a worse lie than silence. The counter increments only after the guest list is in hand.
+
+Red-proofs 7 and 8, both observed failing: removing the call →
+`no liveness observable after 10 sweeps — silence is indistinguishable from a dead watchdog`;
+moving the increment above the error return →
+`an aborted sweep was counted as healthy (sweeps=20)`.
+
 # felhom-agent — Changelog
 
 ## v0.108.0 — F-LEAK: the pool-adoption fix was WRONG; the fix is a path-scoped ACL (2026-07-28)