Two distinct Mac UI Chat failures captured in PR 5312's CI:
1. /api/inference/load 500 with FileNotFoundError on config.json for
unsloth/gemma-3-270m-it-GGUF (a GGUF-only repo). Run 25487410091.
Root cause: detect_gguf_model_remote in
studio/backend/utils/models/model_config.py had a single
hf_model_info call with no retry. On a transient HF Hub flake
it returned None silently, the route at routes/inference.py:592
treated the repo as non-GGUF, and dispatched to the MLX
orchestrator. The orchestrator's _build_model_config re-ran
from_identifier in the subprocess (this time succeeding,
logging "Detected remote GGUF") but then handed an is_gguf=True
ModelConfig to MLXInferenceBackend.load_model, which ignored
is_gguf and called FastMLXModel.from_pretrained →
mlx_lm.utils.load_model → opened a non-existent config.json on
the GGUF-only repo. Fix:
a) detect_gguf_model_remote retries up to 3 times with 1/2/4s
backoff, bypassing retry on RepositoryNotFoundError /
GatedRepoError / RevisionNotFoundError / EntryNotFoundError
(those are permanent).
b) MLXInferenceBackend.load_model now raises a clear
RuntimeError if config.is_gguf=True, instead of letting
mlx_lm surface a cryptic 'config.json does not exist'.
2. Playwright pipeTransport.js 'Unexpected end of JSON input' on
macos-14 free runners. Runs 25489049059 + 25489429306. Chromium
browser process dies mid-test → driver Node process can't parse
the truncated JSON-RPC line and exits. Hits ~50% of runs (well
above acceptable flake). Fix: retry the chat-UI step up to 3
times, FULLY resetting Studio (kill, reset-password, reboot,
/api/health wait, re-export STUDIO_OLD/NEW/NEW2_PW) between
attempts so the change-password flow finds a fresh bootstrap on
each retry. Same retry shape on the extra-UI step. Real
assertion / timeout failures don't match the JSON-input pattern
so they bypass retry and surface immediately. Updated the
install-step comment to drop the now-incorrect '1.55-1.57 ship a
Node 22 driver' claim — all 1.55-1.58 Mac drivers are Node 24,
the racy crash is in pipeTransport itself.
d35bf6ac8e