fix(skill): pre-scan circular/broken symlinks to prevent ENAMETOOLONG crash

[litown]

Issue for this PR

Fixes #27638

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

On Bun runtime, opencode crashes with ENAMETOOLONG during skill scanning when external skill directories (~/.claude/skills/, ~/.agents/skills/) contain circular or broken symlinks. The glob library with follow: true enters infinite recursion on circular symlinks, and Bun's readdir throws ENAMETOOLONG when path strings exceed PATH_MAX. Node.js handles this gracefully, but Bun does not.

This PR adds a pre-scan step (findBrokenSymlinks) that recursively detects circular symlinks (via readlink + path resolution + realpath visited set) and broken symlinks (via stat ENOENT/ELOOP), then passes detected paths as glob ignore patterns. A subdirs option limits the pre-scan to only directories glob would traverse (e.g., only skills/ under ~/.claude/), reducing pre-scan time from ~1.3s to ~19ms.

Related work: PR #18670 addresses the same root cause with a more fundamental approach (replacing glob with a custom cycle-safe walker). However, #18670 targets an older codebase (pre-Effect-TS, zod-based) and likely needs significant rework to merge. This PR is adapted to the current Effect-TS codebase and provides an immediate fix.

Changes:

• packages/core/src/util/glob.ts: Expose ignore option in Glob.Options
• packages/opencode/src/skill/index.ts: Add findBrokenSymlinks() with recursive symlink detection, SCAN_IGNORE_PATTERNS for standard deep directories, and pass results as glob ignore in all scan call sites

How did you verify your code works?

• Verified on ~/.claude/skills/ with 5 broken symlinks and 3 circular symlinks
• Pre-scan with subdirs filter: 19ms (vs 1283ms without filter)
• Glob scan with filtered ignore: 439ms, 1819 files found, no crash
• TypeScript compilation passes (tsc --noEmit)
• Tested with Node.js runtime: glob completes in 73ms without crash
• Tested with Bun runtime: previously crashed with ENAMETOOLONG, now completes successfully

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

🤖 Generated with Claude Code

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found a potentially related PR:

PR #18670: fix(opencode): avoid symlink-loop recursion during skill discovery

This PR appears to address a similar issue - preventing symlink loops/recursion during skill discovery. While it's a historical PR, it's worth reviewing to ensure the current fix (PR #27639) doesn't duplicate or conflict with the approach taken there.

[github-actions]

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