fix: clamp output token count to prevent negative values

When a provider reports reasoningTokens > outputTokens (observed

with kimi-k2.5 thinking variant via Kilo gateway), the subtraction

in getUsage produces a negative output token count. This propagates

into the TUI, extension UI, session exports, and lifetime stats.

Clamp the result to zero to prevent negative display values.

Fixes #9168

Made-with: Cursor

Author: singhvishalkr

packages/opencode/src/session/index.ts

@@ -316,7 +316,7 @@ export namespace Session {
     const tokens = {
       total,
       input: adjustedInputTokens,
-      output: safe(outputTokens - reasoningTokens),
+      output: Math.max(0, safe(outputTokens - reasoningTokens)),
       reasoning: reasoningTokens,
       cache: {
         write: cacheWriteInputTokens,