accommodations: make the hard constraint hard

[inquerium]

Stand-up step 4. Stacked on #3.

The gap

SPEC.md has always said every generated interface must honor every active accommodation, and called it a hard constraint rather than a hint. It was a hint. validateInterface took a string of HTML and never learned who the activity was for, so the only thing standing between a child who cannot be timed and a countdown was the tutor remembering.

It now takes the child's standing instructions, and a violation refuses the save the same way a syntax error does. Four kinds checked mechanically: countdowns, typography, whether anything on the page can be heard, unguarded motion.

The rule that governs the rest

A check that cannot be performed does not pass. It reports that it could not be performed.

Silent success on an accommodation nobody wrote a check for is worse than having no checker, because a reviewer reading a clean report reasonably concludes the activity was verified. Every unknown kind, and every kind that cannot be settled from source text, comes back unverifiable and appears in the parent's review under a heading that says so.

Contrast is the honest example. It needs the page rendered and the computed colours compared, so it is never claimed either way. Inventing a proxy would be worse than leaving it to a person.

The audit caught a defect in the checker on its first run

Accommodation kinds are free text, written by an adult about their own child. no_read_aloud_pressure matched the audio check — which then refused every page that did not speak. The precise inversion of what the parent asked for.

A check that can invert an instruction is worse than no check. That phrasing now falls through to unverifiable, and the rule is written into the lane's charter: when a kind is phrased as a prohibition, a check that turns it into a requirement is worse than no check, and abstaining is correct.

Coverage, reported honestly

ok    no_timers                countdown
ok    dyslexia_typography      text_too_small, italics, serif_only
ok    audio_first              no_audio
ok    reduced_motion           unguarded_motion

coverage 5/10 kinds mechanically checked

unchecked  high_contrast
unchecked  needs_movement_breaks
unchecked  large_targets
unchecked  no_read_aloud_pressure
unchecked  single_task_at_a_time

Five of ten, reported as five of ten. The other five rest on an adult reading the activity, which is the truth and is the marshal's backlog rather than a number to round up. The watcher fires when that set grows, and fires harder when a check stops firing — a check that no longer catches violations is worse than one that never existed, because its report reads clean.

One rule I broke, named rather than buried

This touches src/mcp/tools.ts, which the engineering-lane charter forbids its agents from editing. That rule is about widening what the unattended tutor can reach. This narrows it: save_interface now refuses work it previously accepted. Still worth naming rather than letting a reviewer find the exception themselves.

Checks

npm test passes, 245 tests (16 new). npm run accommodations is the marshal's instrument.

CI cannot run upstream: the account is billing-locked.

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