fix(session): clamp output token count to prevent negative values (#9168)

Author: kagura-agent

packages/opencode/src/session/index.ts

@@ -316,14 +316,22 @@ export namespace Session {
     const tokens = {
       total,
       input: adjustedInputTokens,
-      output: safe(outputTokens - reasoningTokens),
+      output: safe(Math.max(0, outputTokens - reasoningTokens)),
       reasoning: reasoningTokens,
       cache: {
         write: cacheWriteInputTokens,
         read: cacheReadInputTokens,
       },
     }
 
+    if (reasoningTokens > outputTokens) {
+      log.warn("reasoningTokens exceeds outputTokens", {
+        model: input.model.id,
+        outputTokens,
+        reasoningTokens,
+      })
+    }
+
     // kilocode_change start - Use provider-reported cost when available for OpenRouter/Kilo
     const reported = KiloSession.providerCost({
       metadata: input.metadata,