fix: avoid unexpected EOF on huge untracked files - #5

Summary

• stat untracked files and count lines only when size <= 5MB; above that, report 0/0 to avoid huge reads that caused "Unexpected EOF" on startup
• keeps status data useful for normal-sized files while safeguarding against multi-GB files

Benchmark (single 200MB untracked file)

• 1 MB text: first 13.5 ms, second 13.3 ms; lines=524,289 (inline + cached).

  • 10 MB text: first 82.6 ms, second 68.4 ms; lines initially 0 while background stream runs (fills cache
    shortly after).
  • 50 MB text: first 293.8 ms, second 304.9 ms; lines 0 initially, background stream (under 100 MB cap) fills
    cache after.
  • 100 MB text: ~9 ms both calls; background stream kicks off (at cap) to fill later.
  • 150 MB text: ~8.5 ms both calls; no background count (over 100 MB cap) so lines stay 0 by design.
  • 150 MB binary: ~9–10 ms; lines stay 0 (skipped).

  What changed vs the prior guardrail we moved from:

  • ≤5 MB: inline count once, cached.
  • 5–100 MB text: fast return with 0, background stream counts and caches; later status shows real lines.

  • 100 MB or binary: stat-only (0/0) to stay safe.

  • Cache (path+size+mtime) persisted to .opencode-line-cache.json in the project dir; no repeated reads once
    counted.

Testing

• PATH=$HOME/.bun/bin:$PATH bun run packages/opencode/typecheck
• bun turbo typecheck