build: the libavr pin advances past the audit sweep, and two gates start meaning something

The pin crosses libavr's phase-6 close and the guideline sweep behind it.
All 37 chips green, 43 tests each, the README size table matching every
built image, and all 13602 flash images byte-identical to the previous pin.

The bump broke one gate and exposed another as ornamental.

`check_unit.cmake` matched the autobaud loader's measured unit by the symbol
`unit_E`; libavr's rule-46 sweep renamed the member to `m_unit`, which the
mangling spells `6m_unitE`. On the RAM-home chips the check went red and said
so. On the GPIOR chips it went green - the branch that asserts the unit is
*not* in RAM passes on an empty match, and an empty match is what a stale
regex returns for every image. Both branches mean something again.

`tools/check.sh` ran the 37-chip loop under `set -e`, so the first red chip
ended the gate and the 36 behind it were never built - a stale size canary on
attiny13 would have been an alibi for every loader after it. It accumulates
now and fails at the end naming every red preset, which is the shape libavr's
own check.sh carries and the reason it carries it.

The port's own sweep, verified by byte identity: the four TSB tiers' 16-byte
info block is `std::to_array` rather than an extent written beside the
sixteen elements the compiler can count, the three-member serial and loader
configs break one member per line, the turn-around loops are braced, and the
test fixture's config pair is a deduced `std::array` (rules 36, 40, 34). Two
comments stop narrating how the code came to be and one stops citing a repro
at a path it left two phases ago (rules 12, 13).

pureboot's identity stamp stays the raw array rule 36 bans, and now says why:
its reads must fold to immediates because the bytes are in program memory and
a formed address is dereferenced as data space. As a `std::array` the read
loop stopped unrolling and emitted exactly that - measured at +8 B and a
wrong answer on the wire.

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

tools/check.sh

@@ -24,18 +24,32 @@ CHIPS=(attiny13 attiny13a attiny25 attiny45 attiny85
 REFLECT_SPOT=(attiny13a attiny85 atmega8 atmega16a atmega32a atmega48pa
               atmega88 atmega168pa atmega328p atmega164a atmega644p atmega1284)
 
+# Every preset runs even after one goes red, and the gate fails at the end
+# naming all of them: stopping at the first failure turns a red - a stale size
+# canary above all - into an alibi for every chip behind it, and a loader can
+# ship on a chip this gate has not compiled since.
+red=()
+run_preset() {
+	echo "==== $1 ===="
+	cmake --workflow --preset "$1" "${@:2}" || red+=("$1")
+}
+
 for chip in "${CHIPS[@]}"; do
-	echo "==== $chip ===="
-	cmake --workflow --preset "$chip-generated" "$@"
+	run_preset "$chip-generated" "$@"
 done
 
 if ((full)); then
 	for chip in "${REFLECT_SPOT[@]}"; do
-		echo "==== $chip reflect ===="
-		cmake --workflow --preset "$chip-reflect" "$@"
+		run_preset "$chip-reflect" "$@"
 	done
 fi
 
+if ((${#red[@]})); then
+	printf '==== red presets ====\n' >&2
+	printf '  %s\n' "${red[@]}" >&2
+	exit 1
+fi
+
 # Every tree is freshly built now - the one moment the README's size table
 # can be held to what the images measure (a per-preset ctest sees only its
 # own chip; the table needs all of them, and ungated it drifts: a