Three left over from earlier fixes in this work:

- the frame tests asserted 93 was a valid TRAINING length. SimpleTuner's rule
  is 8n+1, not generation's 4n+1, and it rounds down silently — which is why
  frame_problems() rejects 93 and says a good clip can still be a bad sample.
  Reversed: the valid cases are 8n+1 now, and 93 has its own case asserting
  the message explains itself.
- the trainer stopped dumping "Last output" when it started picking the error
  lines out of a bounded tail; the test still looked for the old wording.
- the vendoring test counted the __pycache__ the container writes into the
  bind-mounted copy as "vendored non-source files". Generated, not vendored.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0185zEBiy3KWB37xNGSrxL7w