fix: normalize filepath in FileTime to prevent Windows path mismatch

[JosXa]

Issue for this PR

Closes #20354

Type of change

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

What does this PR do?

On Windows, the Read tool normalizes file paths (forward slashes to backslashes, canonical casing via realpathSync.native) before calling FileTime.read(), which stores the normalized path as a Map key. But Write and Edit tools pass the raw path (often with forward slashes from LLM output) to FileTime.assert(), which looks up the un-normalized key and fails with a false "must read file before editing/writing" error.

The fix adds Filesystem.normalizePath() at the entry of all four FileTime Effect functions (read, get, assert, getLock). This is the single choke point where all file-time operations converge, so normalizing here guarantees consistent Map keys regardless of how callers format the path. On non-Windows platforms, normalizePath is a no-op, so there's no behavioral change.

How did you verify your code works?

1. Typecheck passes
2. All 19 FileTime tests pass (15 existing + 4 new path normalization tests covering forward/backslash combinations for read, get, assert, and withLock)
3. Ran the patched build via bun dev run with the exact repro steps from the issue (Read with forward slashes then Edit/Write with same forward-slash path) - both succeeded without error

Screenshots / recordings

N/A - no UI change

Checklist

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

[github-actions]

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

Based on my search results, I found two related PRs about Windows path normalization that might be relevant:

• PR fix: normalize windows path separators in session queries #20216: "fix: normalize windows path separators in session queries"
• PR fix: normalize windows path separators in session queries #20215: "fix: normalize windows path separators in session queries"

These PRs appear to address similar Windows path normalization issues, though they focus on session queries rather than FileTime specifically. However, they're addressing the same underlying problem of path format inconsistencies on Windows. You may want to verify if there's any overlap in scope or if these should be coordinated.

[github-actions]

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