fix(inject): eliminate race condition in SSE token counting

[DevanshuNEU]

Summary

handleClaudeEvent was calling countTokens() as fire-and-forget per delta chunk, updating summary.outputTokens asynchronously. The finally block read summary.outputTokens immediately after the stream ended — before any of those .then() callbacks had resolved — resulting in consistently under-counted or zero output tokens in STREAM_COMPLETE.

Fix: accumulate all delta text synchronously into a string buffer during the stream, then make a single parallel BPE round-trip for both input and output tokens in the finally block before posting STREAM_COMPLETE. Intermediate batch flushes keep a chars/4 estimate for real-time UI updates.

Type of Change

• fix — Bug fix

What Was Changed

• entrypoints/inject.ts
  • handleClaudeEvent: removed per-chunk countTokens() call from content_block_delta; message_start now sets a synchronous chars/4 input estimate instead of firing an async count
  • decodeSSEStream: added outputTextBuffer string accumulator; each content_block_delta appends text and updates summary.outputTokens via chars/4; finally block awaits Promise.all([countTokens(promptText), countTokens(outputTextBuffer)]) and overwrites estimates with accurate BPE counts before STREAM_COMPLETE is posted

How to Test

1. bun run compile — should exit clean
2. bun run test — all 26 tests should pass
3. Load the extension on claude.ai, send a message, and confirm the [LCO] [Complete] log line shows non-zero input and output token counts

Checklist

• Tests pass locally (bun run test)
• TypeScript compiles clean (bun run compile)
• Extension builds without errors (bun run build)
• No secrets, hardcoded URLs, or sensitive tokens exposed
• Comments are professional and clear — no emojis, no AI-generated filler
• Commit messages follow conventional commits (feat:, fix:, refactor:, test:, chore:)

Notes for Reviewer

The chars/4 approximation used during streaming is intentionally rough — it keeps the UI responsive without any async overhead. The accurate BPE count replaces it atomically in finally before STREAM_COMPLETE fires, so the final stored value is always the precise count. If countTokens times out (5s fallback), the chars/4 estimate is preserved rather than overwriting with zero.