fix(cli): tolerate pre-existing plan directory on OneDrive

[truffle-dev]

Why

Plan mode crashes with EEXIST: file already exists when a kilocode workspace lives on a OneDrive-synced Windows path (#9755). The .kilo/plans directory is a OneDrive ReparsePoint, and Node's fs.mkdir(path, { recursive: true }) still throws EEXIST against ReparsePoint dirs in some Node versions even though recursive: true is supposed to be idempotent. Every plan turn fails before the plan file is written.

What changed

insertPlanReminders now goes through a small ensurePlanDir helper that pre-checks the directory with Filesystem.isDir and only calls mkdir when the dir doesn't already exist. POSIX behavior is unchanged; on the OneDrive ReparsePoint case the throwing mkdir call is skipped entirely.

How to test

bun test ./test/kilocode/ensure-plan-dir.test.ts from packages/opencode/. The new tests cover the missing-dir, idempotent-existing-dir, and recursive-parents cases.

Closes #9755

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• packages/opencode/src/kilocode/session/prompt.ts
• packages/opencode/test/kilocode/ensure-plan-dir.test.ts

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_{Reviewed by gpt-5.5-2026-04-23 · 102,242 tokens}