Fix output text not working.

docs/Decisions.md

@@ -325,3 +325,34 @@ on both engines. Three independent causes, all length-dependent:
 **Revisit:** when Transformers.js changes the seek-loop condition (currently
 `return_timestamps && !max_new_tokens`, `src/models/whisper/modeling_whisper.js`),
 retest whether the explicit `max_new_tokens` is still needed.
+
+## D-022 — Medium models never default to fp16 in the browser
+**Status:** Accepted (2026-07-15)
+Reported symptom: transcribing `en_aiproblem` in-browser with Whisper Medium
+printed just "the". The medium catalog entries defaulted to fp16 on WebNN
+(whole model) and WebGPU (encoder) — and D-017's "auto" order now tries WebNN
+first, so browsers exposing `navigator.ml` silently moved medium onto fp16.
+Two problems with those fp16 conversions
+(`onnx-community/whisper-medium(.en_timestamped|-ONNX)`):
+1. The fp16 ONNX files crash onnxruntime's graph optimizer at session
+   creation (`SimplifiedLayerNormFusion` fails on their
+   `InsertedPrecisionFreeCast_*` nodes) — reproduced on both onnxruntime-node
+   and onnxruntime-web 1.26.0-dev (wasm EP). EPs whose optimizer pipeline
+   skips that fusion can load the model and hit problem 2 instead.
+2. Whisper medium/large encoder activations are the classic fp16 overflow
+   case — degenerate output with no error raised.
+Meanwhile q4 medium was verified correct end-to-end on the real browser
+runtime (onnxruntime-web wasm EP driven under Bun via the
+`Symbol.for("onnxruntime")` override, `graphOptimizationLevel: "basic"` as in
+D-014, `max_new_tokens: 440` as in D-021; both the `.en` and multilingual
+conversions, auto language detect included). **Fix:** medium's `webgpu` and
+`webnn` defaults are q4 (`ACCEL_Q4` in `src/lib/models.ts`). A backend that
+cannot execute q4 (`MatMulNBits`) throws at pipeline creation and falls down
+the D-017 device chain — strictly better than silently emitting garbage.
+**Scope:** medium only — that's where load-failure evidence exists.
+tiny/base/small keep fp16 on WebNN and small keeps fp16+q4 on WebGPU;
+large-v3-turbo keeps fp16+q4 on WebGPU (the widely-used Transformers.js demo
+configuration). If a one-word/garbage transcript ever shows up on those, suspect
+their fp16 encoders and extend this decision.
+**Revisit:** if the onnx-community medium conversions are re-exported with
+working fp16 files, or once WebNN/WebGPU runs can be exercised in CI.