The playbook covered why a run is SLOW. It did not cover the more expensive
failure: a run that COMPLETES, reports plausible numbers, and is wrong about
itself. Seven of those turned up on the Gemma-4 ERP/RP tune between 08-24 and
08-26 and not one raised an error.
New §4, seven landmines plus a pre-launch checklist:
4.1 a cache key must cover the MEANING of the cached thing. The encode
cache missed the impersonation mask; run 2 would have reused run 1's
unmasked encodings and written impersonation_mask_sha256 into its own
manifest while doing it. No error, no count change, normal loss curve.
4.2 validating a VALUE is not validating the PARAMETER. warmup_ratio was
in range and deleted from transformers 5. Build kwargs as data and
diff the NAMES against the installed signature -- you cannot check the
argument list of a call you have already made.
4.3 record what the run RESOLVED to, never what it requested. Run 1
recorded no attention backend, so an MFU panel profiled the serving
seat under sdpa and recommended adopting flex_attention for a run that
was already using it.
4.4 never train from a dirty tree; harness_commit will name a commit that
does not describe the run. Annotate afterwards, never edit the shipped
artifact -- and state what is NOT wrong, or the note casts doubt on
every field it omits.
4.5 a watchdog whose pgrep pattern appears in its own argv can only ever
return "alive". The inert-gate shape in a liveness check.
4.6 an instrument nobody runs is not an instrument. Mutation-check any
test guarding a property that fails silently.
4.7 fix a stale measurement at the source. "~4.3 HOURS to rebuild the
encode cache" (really 145.5 s) was copied into a new launcher by the
same person who had just measured the real number.
4.8 the pre-launch honesty checklist, ten minutes.
Also:
- Header and framing widened. The file is now a training playbook with a
throughput half and an integrity half; the filename stays for inbound links.
- Sections 4-7 renumbered to 5-8. External refs are all to §1.1 and §3.4 and
are unaffected.
- Four rows added to the superseded-claims table, including the kernel table /
68% quadratic / 8.6% MFU set, which describe the serving seat rather than
the training run.
- gemma4-erp-tune-sizing.md §6 carries a correction banner with the explicit
falls/survives split, because that is the doc someone actually reads before
a run.
vh
dae6ede8e2