fix: prevent Playwright MCP error flood from crashing OpenCode

[vmlinuzx]

Summary

Fixes the infinite JSON parse error loop that makes OpenCode unrecoverable when using the /playwright skill.

Problem

When Playwright MCP outputs non-JSON-RPC data to stdout (npm download progress, browser console logs, debug output), the MCP SDK's JSON parser throws repeatedly in a while(true) loop, flooding the system with thousands of errors per second and causing OpenCode to freeze.

Root Cause

The MCP SDK's stdio transport (@modelcontextprotocol/sdk) has a processReadBuffer() method with this pattern:

while (true) {
  try {
    const message = this._readBuffer.readMessage();
    if (message === null) break;
    this.onmessage?.(message);
  } catch (error) {
    this.onerror?.(error);  // Error is caught but loop CONTINUES
  }
}

When garbage hits stdout, each line throws, the error is reported, and the loop continues - creating a denial-of-service on the error handler.

Solution

1. Suppress npm output (quick fix)

Added --yes --quiet flags to npx in the playwright skill config to prevent npm from outputting download progress.

2. Error rate limiting (defensive fix)

Added error rate limiting to SkillMcpManager:

• Tracks errors per client with sliding 1-second window
• If >50 errors occur within 1 second, automatically kills the MCP client
• Subsequent operations on killed clients throw a descriptive error explaining what happened

Changes

File	Changes
src/features/builtin-skills/skills.ts	Added --yes --quiet to npx args
src/features/skill-mcp-manager/manager.ts	Added ErrorRateTracker, error rate limiting logic
src/features/skill-mcp-manager/manager.test.ts	Added 2 tests for error rate limiting
docs/issues/playwright-mcp-infinite-loop.md	Full root cause analysis and documentation

Test Results

bun test src/features/skill-mcp-manager/manager.test.ts
30 pass, 0 fail

Notes

The pre-existing type errors in session-manager/tools.test.ts, skill-mcp/tools.test.ts, and skill/tools.test.ts are unrelated to this change (missing metadata and ask properties in ToolContext).

---

Summary by cubic

Prevents the Playwright MCP from flooding errors and freezing OpenCode by suppressing noisy stdout and terminating runaway clients when error rates spike.

• Bug Fixes
  • Added --yes --quiet to npx in the Playwright skill to suppress npm/npx output.
  • Implemented error rate limiting in SkillMcpManager; kill client if >50 errors occur within 1 second and return a clear error.
  • Added unit tests for the limiting behavior and documented the root cause.

^{Written for commit d05e11a. Summary will update on new commits.}

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Install rate limiter before client.connect

The error‑rate wrapper is installed only after client.connect(transport) completes; any non‑JSON stdout that appears during the initial handshake (e.g., npx download progress or early Playwright logs) will still hit the SDK’s unbounded onerror loop before this handler is attached. That means the original freeze can still happen during startup, which is the most likely time for npm noise. Consider wiring the transport.onerror wrapper before calling client.connect so startup errors are also rate‑limited.

Useful? React with 👍 / 👎.

[cubic-dev-ai]

No issues found across 4 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.