Every checker is Rust now

Six ported, 17 scripts down to 11, 119 tests up to 161. guards, counts, doccheck, compat, protocol and protocol --selftest are obscene-tool subcommands, and the verify.sh stages and CI step point at them.

compat and protocol ported without behavioural change, and both were proved by differential rejection rather than by agreement. compat renders a table compared byte-for-byte against the committed document, so both versions producing "current" means both produced identical markdown. protocol was run against its own thirteen mutations - an unknown verb answered, a sequence going backwards, a capability never announced, a bytes run one nibble too long - and both caught all thirteen. Agreement on clean input proves nothing; that is exactly how the Python guard passed for months while skipping eight rows.

Three things worth keeping from the port itself:

• I guessed three of the protocol's fixed lists rather than reading them, and invented a part verb, a refused reason and a too-long reason while dropping blob, run and gpu. The Python sitting beside it is what made that visible within a minute. Ported lists are transcribed now, not remembered.
• The first protocol tests raced. They shared one temp path under the parallel runner and one test deleted another's file mid-check. A fault in the test rather than the checker, but a flaky gate is a gate people learn to re-run rather than read.
• The first test fixtures did not look like the real transcripts - no ack, no terminal done - so they tripped the dangling-ack rule and tested the wrong thing. Same mistake as the guard fixture earlier in the day: a fixture that does not resemble the thing under test proves nothing about it.

Remaining Python is four analysis scripts and seven generators. Five of the generators are gated in verify.sh, so those are next.