Add section on suppressed tokens for digits

whisper/README.md

@@ -88,6 +88,50 @@ WHISPER_URL=http://minerva.lan:9001
 
 No other change. The Axum server speaks ahmetoner's interface; we mirror it.
 
+## Investigated and rejected
+
+### `suppress_tokens` for digit-sequence preservation (2026-04-28)
+
+Goal: when a dictator says individual digits ("eins null null"), have Whisper
+emit them as words instead of collapsing them to a number ("100"). The
+collapse is irreversible downstream — there is no way for the LLM to
+distinguish "hunderteins" (101 as a number) from "eins null eins" (a 1-0-1
+sequence) once both have become `101` in the transcript.
+
+The standard advice
+([openai/whisper Discussion #1041](https://github.com/openai/whisper/discussions/1041))
+is to set `suppress_tokens` to every numeric token in the vocabulary so the
+decoder is forced onto word tokens. We added a `suppress_numerics` form
+field, threaded it through the Axum server and the experiments sandbox,
+and tested it against a real cardiology dictation.
+
+**Two filter widths, both pathological:**
+
+1. **Jongwook's exact recipe** (`\d+` filter, ~426 tokens, faithful 1:1
+   reproduction with `eot` bound and `removeprefix(" ")` filter):
+   - Massive end-of-audio repetition loop ("Enoxaparin, das heißt
+     Enoxaparin, das heißt Enoxaparin, …" 20+ times). The fixed
+     `compression_ratio_threshold=2.4` did not catch it.
+   - Numbers also disappear: `40 mg Thorazemit` → `Milligramm Thorazemit`
+     (the `40` is dropped, not converted to a word).
+2. **Single-digit only** (`\d` filter, 20 tokens — `0`-`9` with and without
+   leading space):
+   - Repetition loop is gone (small enough list to keep beam search stable).
+   - But dictated sequences disappear entirely: `5mg 100` and `5mg 101`
+     become just `Visoprolol` and `Ramipriel` (no dosing schema in any form).
+   - Collateral damage on natural numbers: `12,5 mg` → `12,25 mg` (the ` 5`
+     token was suppressed; the decoder built the value from multi-digit
+     tokens and duplicated a digit).
+
+There is no usable middle ground between the two widths for our setup
+(`large-v3` + faster-whisper 1.2.1 + medical German dictation). The status
+quo (`100`/`101` in the transcript, doctor corrects manually) stays.
+
+Don't reattempt without changing the underlying ASR (different model,
+different backend, or model-internal training to preserve digit-form
+acoustic information). Memory entry:
+`project_whisper_suppress_tokens_dead_end.md`.
+
 ## Offline mode
 
 ```bash