tighten transport failure semantics

tests/fixtures/README.md

@@ -31,6 +31,18 @@ removed before production firmware was built and flashed.
   capture application opened. That is deliberate evidence of the remaining
   distinction: USB endpoint drain is observable, but application receipt
   requires the planned acknowledgement/replay layer.
+- `direct_usb_3c95f3d.trk` — SHA-256
+  `f495486f094a758bb785e145026e3934d60b52dd5083aef7f5d896195d967869`.
+  This is the validated-frame output from the final exact-commit smoke capture:
+  1,680 contiguous samples, sequences 0 through 1,679, with zero packet/sample
+  gaps, resets, CRC failures, reported drops, loop overruns, trailing bytes, or
+  timestamp saturation.
+- `direct_usb_3c95f3d.wire` — SHA-256
+  `3bdaeadff7962c6eac48c4ebeda285c8eb359e439d5e1728104add2009122c03`.
+  This is the byte-for-byte wire side of the same capture. It contains 563 bytes
+  of startup text before the valid frames. That text includes the literal
+  `TRK1`, producing one rejected candidate header as designed. Extracting all
+  valid frames reproduces `direct_usb_3c95f3d.trk` byte-for-byte.
 
 `tests/test_trikke_protocol.py` verifies the hashes, parses the captures in
 fragmented chunks, and asserts these signatures so the hardware evidence remains