fix(core): stop instruction walk at case-variant Windows project roots - #53349

Issue for this PR

Closes #52874
Closes #50296
Closes #50750
Closes #50857

Type of change

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

What does this PR do?

On Windows, a location's directory keeps whatever spelling the client's CWD had, while the project root comes from git rev-parse --show-toplevel. Starting opencode from cmd after cd /d c:\repo, from a process spawned with a c:\ cwd (IDE terminals, scripts), or via opencode c:\repo gives c:\repo vs C:\repo. PowerShell and Git Bash normalize the drive, which is why this is intermittent across users.

FSUtil.contains(root, start) accepts the pair (path.relative is case-insensitive on win32), but ancestorDirectories compared with ===, never reached stop, and recursed at the drive root (dirname("c:\\") === "c:\\") until the stack overflowed. The plugin's activation guard then marked core/instructions unavailable, so every prompt in that location failed with InitializationBlocked. Non-git directories aren't affected because both sides come from the same fs.resolve.

The fix compares the stop boundary with the existing sameDirectory helper from @opencode/util/path (case-insensitive for Windows drive/UNC paths, unchanged on POSIX):

• ancestorDirectories in the instruction plugin, which fixes the crash.
• FSUtil.up / globUp. Without this, the instruction source's fs.up walk also misses stop and reads AGENTS.md files above the project root, up to c:\. The same up boundary is used by the formatter config lookup (findUp(target, directory, worktree)).

Compared to #50544, which bounds the walk at the filesystem root: that also stops the overflow, but the walk then continues past the project root, so instruction watchers and AGENTS.md reads extend to the drive root.

This doesn't address the duplicate-Location side of the casing problem (#47839). The server still keys c:\repo and C:\repo as separate locations.

How did you verify your code works?

• Reproduced on Windows 11 / Bun 1.4.2 with a regression test in instruction-discovery.test.ts (location c:\...\repo, project C:\...\repo, plus an AGENTS.md above the project). It runs only on win32, which the unit CI matrix covers.
  • Without the fix: fails with Instructions.InitializationBlocked: ... core/instructions.
  • With only the ancestorDirectories change: fails because the AGENTS.md above the project root is included.
  • With both changes: passes.
• bun test for instruction, project, formatter, git, read-tool, config and skill-discovery tests in packages/core, and bun test in packages/util. The only failures (Config > excludes home-level claude..., Config > deduplicates global ecosystem..., global > ... canonicalizes it) fail identically on v2 without this change on this Windows machine.
• bun run check passes, and prettier reports the changed files as formatted.

Screenshots / recordings

Not a UI change.

Checklist

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