fix(openai-adapters): Remove token count validation in finish event handler

Removed the check that required tokens > 0 before emitting usage from
finish event. The finish event should always emit usage if part.usage
exists, even if tokens are legitimately 0.

The fallback to stream.usage Promise now only triggers if:
- No finish event is emitted, OR
- Finish event exists but part.usage is undefined

This fixes cases where finish event has valid 0 token counts.

Co-authored-by: nate <[email protected]>
Generated with [Continue](https://continue.dev)

Author: continue[bot]

packages/openai-adapters/src/vercelStreamConverter.ts

@@ -121,7 +121,7 @@ export function convertVercelStreamPart(
       });
 
     case "finish":
-      // Emit usage chunk at the end if usage data is present and valid
+      // Emit usage chunk at the end if usage data is present
       if (part.usage) {
         const promptTokens =
           typeof part.usage.promptTokens === "number"
@@ -136,34 +136,31 @@ export function convertVercelStreamPart(
             ? part.usage.totalTokens
             : promptTokens + completionTokens;
 
-        // Only emit usage chunk if we have meaningful token counts
-        if (promptTokens > 0 || completionTokens > 0) {
-          // Check for Anthropic-specific cache token details
-          const promptTokensDetails =
-            (part.usage as any).promptTokensDetails?.cachedTokens !== undefined
-              ? {
-                  cached_tokens:
-                    (part.usage as any).promptTokensDetails.cachedTokens ?? 0,
-                  cache_read_tokens:
-                    (part.usage as any).promptTokensDetails.cachedTokens ?? 0,
-                  cache_write_tokens: 0,
-                }
-              : undefined;
+        // Check for Anthropic-specific cache token details
+        const promptTokensDetails =
+          (part.usage as any).promptTokensDetails?.cachedTokens !== undefined
+            ? {
+                cached_tokens:
+                  (part.usage as any).promptTokensDetails.cachedTokens ?? 0,
+                cache_read_tokens:
+                  (part.usage as any).promptTokensDetails.cachedTokens ?? 0,
+                cache_write_tokens: 0,
+              }
+            : undefined;
 
-          return usageChatChunk({
-            model,
-            usage: {
-              prompt_tokens: promptTokens,
-              completion_tokens: completionTokens,
-              total_tokens: totalTokens,
-              ...(promptTokensDetails
-                ? { prompt_tokens_details: promptTokensDetails as any }
-                : {}),
-            },
-          });
-        }
+        return usageChatChunk({
+          model,
+          usage: {
+            prompt_tokens: promptTokens,
+            completion_tokens: completionTokens,
+            total_tokens: totalTokens,
+            ...(promptTokensDetails
+              ? { prompt_tokens_details: promptTokensDetails as any }
+              : {}),
+          },
+        });
       }
-      // If no valid usage data, don't emit a usage chunk
+      // If no usage data in finish event, return null
       return null;
 
     case "error":