gateway: instrument the audio per-request helper (speech still bills $0)

Speech billed $0.000000 across three deploys while transcription billed
$0.010000 exactly, so the patch works for one audio call type and not the other.
Three hypotheses have now been retired (hidden-params early return; missing
character price; lookup miss) — the remaining question is WHERE the speech cost
is lost, and guessing is more expensive than measuring.

The helper now prints, for TTS/STT models only, whether it ran at all, what it
could see (custom_pricing keys, shared cost-map hits) and what it resolved, into
the app log. If those lines never appear for a speech call, the request never
reaches the model cost calculator and the loss is upstream of this patch.

Also fixes a real defect in the previous revision: the addition was wrapped in a
bare except, so a TypeError from a None base cost would have been swallowed
silently — which is exactly the sort of silence that made this take three
deploys. It now coerces a None base to 0.0 and reports any failure.

patch_audio_request_cost.py

@@ -56,18 +56,26 @@ HELPER = '''def _coop_per_request_cost(
     logging layer builds from our config.yaml model_info, then the shared cost
     map, then the call metadata. Inert unless a model declares the field.
     """
+    def _is_audio(name: Any) -> bool:
+        text = str(name or "").lower()
+        return "tts" in text or "whisper" in text
+
+    cost_map = {}
+    try:
+        import litellm as _litellm  # local import: not every caller binds it globally
+        cost_map = getattr(_litellm, "model_cost", {}) or {}
+    except Exception:
+        cost_map = {}
+
     candidates = []
     if isinstance(custom_pricing, dict):
         candidates.append(custom_pricing)
-    try:
-        import litellm as _litellm  # local import: not every caller binds it globally
-        cost_map = _litellm.model_cost
+    map_hits = []
     for key in (litellm_model_name, model):
         entry = cost_map.get(key) if key else None
         if isinstance(entry, dict):
             candidates.append(entry)
-    except Exception:
-        pass
+            map_hits.append((key, entry.get("input_cost_per_request")))
     try:
         details = getattr(litellm_logging_obj, "model_call_details", None) or {}
         info = (details.get("metadata") or {}).get("model_info")
@@ -75,6 +83,22 @@ HELPER = '''def _coop_per_request_cost(
             candidates.append(info)
     except Exception:
         pass
+
+    # Diagnostic (audio models only): did this run at all, and what could it see?
+    # If this line never appears for a speech call, the request never reaches the
+    # model cost calculator and the loss is upstream of this patch.
+    if _is_audio(model) or _is_audio(litellm_model_name):
+        try:
+            print(
+                "[coop-audio] probe"
+                f" model={model!r} litellm={litellm_model_name!r}"
+                f" custom_pricing={sorted(custom_pricing) if isinstance(custom_pricing, dict) else type(custom_pricing).__name__}"
+                f" map_hits={map_hits!r} candidates={len(candidates)}",
+                flush=True,
+            )
+        except Exception:
+            pass
+
     for candidate in candidates:
         try:
             value = candidate.get("input_cost_per_request")
@@ -82,9 +106,20 @@ HELPER = '''def _coop_per_request_cost(
             continue
         if value:
             try:
-                return float(value)
+                resolved = float(value)
             except (TypeError, ValueError):
                 continue
+            if _is_audio(model) or _is_audio(litellm_model_name):
+                try:
+                    print(f"[coop-audio] resolved per_request={resolved}", flush=True)
+                except Exception:
+                    pass
+            return resolved
+    if _is_audio(model) or _is_audio(litellm_model_name):
+        try:
+            print("[coop-audio] resolved per_request=0.0 (nothing declared)", flush=True)
+        except Exception:
+            pass
     return 0.0
 
 
@@ -107,14 +142,21 @@ PATCHED_RETURN = """                region_name=region_name,
         # declares nothing; the early "provider reported the cost" return above
         # is unaffected.
         try:
-            response_cost = response_cost + _coop_per_request_cost(
+            _coop_pr = _coop_per_request_cost(
                 model=model,
                 litellm_model_name=litellm_model_name,
                 custom_pricing=custom_pricing,
                 litellm_logging_obj=litellm_logging_obj,
             )
-        except Exception:
-            pass
+            response_cost = (response_cost or 0.0) + _coop_pr
+            _coop_name = str(model or "") + str(litellm_model_name or "")
+            if "tts" in _coop_name.lower() or "whisper" in _coop_name.lower():
+                print(
+                    f"[coop-audio] add per_request={_coop_pr!r} -> response_cost={response_cost!r}",
+                    flush=True,
+                )
+        except Exception as _coop_exc:
+            print(f"[coop-audio] add failed: {type(_coop_exc).__name__}: {_coop_exc}", flush=True)
 
         return response_cost
     except Exception as e: