fix(power): exempt charge-limit oneshot from start rate limiting

Round 1 of #101's V3 failed on TuringMachine (2026-07-13 18:16): a
SPACED dock/AC event storm — each run finishing before the next event —
never coalesces, so 5 successful sub-second starts inside systemd's
default 10s window tripped start-limit-hit and marked the unit failed
(doctor badge) although every run succeeded. The write is idempotent
and cheap; rate limiting it only manufactures false failures, so the
unit sets StartLimitIntervalSec=0.

checks.battery-charge-limit now asserts the exemption and runs 8
sequential starts expecting a clean, non-failed state; the original
mid-run coalescing phase is unchanged.

Verified: V2 — the check passes under KVM (exit 0). V0 flake check
green. V3 round 2 re-queued in HARDWARE-QUEUE.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

flake.nix

@@ -805,6 +805,29 @@
               )
               assert "start-limit-hit" not in service_log, service_log
               assert "Failed with result" not in service_log, service_log
+
+              # SPACED storm (T14s, 2026-07-13): when each run finishes
+              # before the next AC event arrives nothing coalesces, and 5
+              # successful starts inside systemd's default 10s window mark
+              # the unit failed (start-limit-hit) although every run
+              # succeeded. The unit must stay exempt from start rate
+              # limiting — assert the exemption, then prove repeated
+              # back-to-back starts leave a clean state.
+              machine.succeed(
+                  'test "$(systemctl show -p StartLimitIntervalUSec --value '
+                  'nomarchy-battery-charge-limit.service)" = 0'
+              )
+              machine.succeed(
+                  "for i in $(seq 1 8); do "
+                  "systemctl start nomarchy-battery-charge-limit.service; done"
+              )
+              machine.fail(
+                  "systemctl is-failed --quiet nomarchy-battery-charge-limit.service"
+              )
+              service_log = machine.succeed(
+                  "journalctl -b -u nomarchy-battery-charge-limit.service --no-pager"
+              )
+              assert "start-limit-hit" not in service_log, service_log
             '';
           };