Support Windows paths and directory separators in path tab completion

[nordicnode]

Support Windows paths and directory separators in path tab completion

Summary

• In cli/src/hooks/use-path-tab-completion.ts, fix path tab completion and automatic directory navigation on Windows.
• Previously, usePathTabCompletion checked searchQuery.startsWith('/') || searchQuery.startsWith('~') for absolute paths. On Windows, drive paths (C:\...) and UNC paths were not matched, causing them to fall through to the relative path branch (path.join(currentPath, searchQuery)).
• Furthermore, completed.endsWith('/') was used to detect full directory completions. On Windows, path-completion.ts appends path.sep (\), so completed.endsWith('/') was always false, breaking automatic directory navigation when pressing Tab.
• Exports pure helpers isAbsolutePath, isCompleteDirectory, and toRelativePath from use-path-tab-completion.ts to handle both POSIX and Windows path styles.
• In cli/src/hooks/__tests__/use-path-tab-completion.test.ts, uses the exported implementations and adds test cases for Windows drive paths and backslash directory completions.

Test plan

[✓] bun test --config=/dev/null src/hooks/__tests__/use-path-tab-completion.test.ts — 35 pass, 0 fail
[✓] bun run --cwd cli typecheck — 0 errors
[✓] PR hygiene check passed

[codebuff-team]

Good catch and a clean fix. The core bug is real: usePathTabCompletion only recognized POSIX-style absolute paths (/, ~), so Windows drive paths (C:\...) fell into the relative-path branch and got mangled via path.join(currentPath, searchQuery). Likewise, checking only completed.endsWith('/') broke auto-navigation on Windows since path-completion.ts appends path.sep (\) there.

Extracting isAbsolutePath, isCompleteDirectory, and toRelativePath as exported pure functions is the right move — it lets the test file exercise the actual implementation instead of a hand-duplicated copy (the previous tests were testing dead code, not the hook). That's a meaningful improvement on its own.

A couple of things worth double-checking before porting:

• isCompleteDirectory now treats a trailing \ as a directory marker unconditionally, even on POSIX, where a filename literally ending in \ is legal (rare, but possible). Probably fine, just flag it.
• isAbsolutePath calls both path.isAbsolute and path.win32.isAbsolute regardless of platform — intentional per the PR description, and reasonable since you want Windows-style paths recognized even if the CLI happens to run under WSL/POSIX, but worth a comment noting this is deliberate cross-platform detection, not a mistake.

Small, in-scope, tested, addresses a real cross-platform bug. This is the kind of PR worth porting by hand.