fix(opencode): atomic storage writes with retry/backoff + quarantine on Windows; tolerant reads

[KakashiTech]

What

• Atomic write on Windows: temp → fsync(file) → rename → fsync(dir) with retry/backoff on open/rename.

• Tolerant reads: retries on transient FS errors; if JSON is corrupt or retries exhaust, move to quarantine instead of crashing.

• Quarantine: preserve data when rename/open is blocked (AV/sharing) and when JSON is malformed.

• Tests: invalid JSON → quarantine; rename failure (target path is a directory) → quarantine.

Why (Windows)

• Corporate AV often causes transient sharing violations leading to UV_UNKNOWN on open/rename (e.g. ...storage\part\msg_\prt_.json). This made storage unusable for some users (Error: UV_UNKNOWN: unknown error #8792).
• This change keeps storage responsive by retrying transient errors and safely isolating bad/locked files.

Details

• Retries: 6 attempts, exponential backoff (≈50ms → 1.6s).
• Temp file name: .oc-<basename>.<pid>.<ts>.tmp in the same directory.
• Directory/file fsync used where supported; failures are tolerated safely.
• Quarantine path: storage/quarantine/<timestamp>/<relative-original-path>.json.

Verification

• bun install and bun test: 789 passing, 0 failing.
• Manual: on Windows with Defender enabled, confirm no hard crash, and that corrupt/locked files end up in quarantine when needed.

Trade-offs

• Slight I/O overhead from fsync and retries, bounded and only on contention.
• Creates a quarantine folder for recovery workflows.

Links

• Fixes Error: UV_UNKNOWN: unknown error #8792

[github-actions]

Hey! Your PR title feat(storage, windows): atomic write + retry/backoff, quarantine; tolerant reads; tests doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

No duplicate PRs found

[Musti94AI]

I have tested this and your solution seems to work @KakashiTech
I am running OpenCode locally and no issues until now.

[Musti94AI]

I tried the fix the last couple of days and I had no problems at all! Works perfectly :)
@rekram1-node Thanks in advance for the review! Looking forward to getting this merged. And thank you @KakashiTech !

[jnargi]

Confirm this solution works, hope this gets merged into main soon