review: fix review findings (correctness, hardening, doc-accuracy)

First recursive code-review-harness pass over the authored SDK code (sim/,
config-lint, flowgen, drivers/{relays,freshness}, build/, ci.yml). Four parallel
dimension reviewers; all findings at every severity corrected per workspace rule.

Correctness / reliability:
- freshness.c min_budget_ms: use a `seen` flag, not `best==0`, as the empty
  sentinel — a zero-tolerance (max_stale_ms==0) binding was silently widened to a
  looser neighbour's budget. Regression test added; still 66/66 MC/DC.
- config-lint parse_reserved_ranges: match `reg` as a whole property token (ident
  boundary before, `=` after) so `reg-names` / a `region-*` label no longer
  mis-parses into a bogus reserved range.
- config-lint loader check: fail closed — flag any loader with a LOAD_ADDR that is
  not a known-safe boot component, instead of only known MCU names, so a future
  coprocessor ("Rtos"/"Bl32") can't slip past the 0x40000-brick gate.
- build-kernel.sh: sha256 verification is now mandatory (refuse to build if the pin
  is missing) and the mktemp scratch tree is removed on exit (trap), while a
  caller-provided WORK is left intact for CI artifact upload.

Test quality:
- freshness: added the age==max_stale boundary case and a clock-wraparound
  (now < last_ok) fail-safe-to-UNKNOWN test.
- relays: unsetenv(WARDEN_GPIO_ROOT) at main() so the NULL-env arm is hermetic.

Security / CI:
- ci.yml: top-level `permissions: contents: read` (badges overrides to write);
  pin taiki-e/install-action to commit SHA (v2.86.7).

Maintainability / docs:
- drivers/enforce-mcdc.sh: one shared, name-derived gate replaces the two
  copy-pasted per-driver scripts; Makefiles call ../../enforce-mcdc.sh.
- docs/architecture.md: §3/§4/§6/§7 rewritten to match reality — NPU/RGA models,
  config-lint, and the relays+freshness MC/DC harnesses are done; kernel §6 now
  reflects the 5.10->6.18.46 forward-port (ADR-0001), not the superseded plan44/6.6.
- README: status blurb + layout table corrected (kernel/, .github/; stale ci/ and
  patches/ descriptions fixed). hpmcu "8 tests" -> 7 in docs.
- freshness.{c,h}: ADR reference points at flare-edge ADR-0004 (warden-sdk's
  ADR-0004 is the CI runner — number collision).
- normalize rustfmt drift across sim/ + config-lint.

All green: sim 37 tests, config-lint 8 tests, both drivers 100% MC/DC (relays
40/40, freshness 66/66), clippy clean under -D warnings, gitleaks clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017wB8KB3MMQztRDXCMCkPrf

drivers/relays/test/test_relays.c

@@ -211,6 +211,11 @@ static void integration_tests(void)
 
 int main(void)
 {
+    /* Hermeticity: layer 1's fake-io tests exercise gpio_root()'s `r && *r` NULL
+     * arm (unset env). Clear any inherited WARDEN_GPIO_ROOT so that outcome is
+     * deterministic instead of depending on the ambient shell (an exported value
+     * would otherwise drop condition coverage and spuriously fail the gate). */
+    unsetenv("WARDEN_GPIO_ROOT");
     unit_tests();
     integration_tests();
     fprintf(stderr, "%d checks, %d failures\n", g_checks, g_fail);