[CameronBrooks11]

Fixes #81, the GET_STATE replies cut short on the gen2 Nano.

The 2026-11-01 bisect (#84) traced the cut-short replies to how often the loop masks interrupts. With main.cpp's masked windows removed, or with the loop slowed by 300 us a pass, the bad-reply rate went from 187 in 300 s to 0. relayControlLogic() opened four masked windows on every pass: three snapshots and the on-time commit.

What changes:

• relayControlLogic() takes its snapshot, runs the PIDs and publishes the on-times only on a new thermocouple reading, or once RLHT_SNAPSHOT_INTERVAL_MS (default 10, a -D override) has passed. In between, actuateRelay() drives from the last snapshot.
• The PIDs still compute once per reading (fix(firmware): compute the heater PIDs once per thermocouple reading #76), since a reading always triggers a snapshot.
• The e-stop, watchdog-trip and fault hold is checked on every pass with no masked window. Each flag is one byte and only the main loop sets them. The relay state fields are written only when they change.
• A command now waits up to the interval to reach a relay: 10 ms, next to a 1000 ms relay period.
• An invalid mode now holds both relays off through drives of 0, where before it returned early from each pass.

I rejected a per-command "changed" flag set by every handler: a handler that missed setting it would leave a stale setpoint or mode. A fixed interval can't miss anything.

Test

test_mask_rate counts noInterrupts() calls through the host stub over 3 s of closed-loop heating:

	Passes that opened a masked window
main's relayControlLogic()	1500 of 1500: the check fails
this branch	302 of 1500, against an allowance of 312 (one per 10 ms plus one per reading)

It also checks that a duty change reaches relay 1 within the interval (10 ms) and that the e-stop drops relay 1 on the next pass.

make -C test/host: 732 ok, 0 failed, across the four envs. That's main's 696 plus test_mask_rate's 36.

pio run, 0 warnings:

env	Flash	RAM	Flash vs main
gen1_nano	23018 B	918 B
gen2_nano	24246 B	934 B	+208 B, +12 B RAM
gen1_nanoevery	24505 B	996 B
gen2_nanoevery	25717 B	1014 B

Bench

gen2 Nano on the backplane, Pi 4 at 50 kHz, replylog.py 19 1 300 with retries off:

Build	Bad replies in 300 s
main a251158 (2026-11-01, two captures)	187 / 2552 and 175 / 2552
this branch (2026-11-02)	1 / 2551

The one bad frame went to 0xFF at the CRC byte and was caught. That's the rate Slice_DCMT's gen2 Nano showed on the same bus on 2026-10-31 (1 / 2555).

Not run on the board: the heaters under closed-loop control on this build. The host tests cover the control paths.