[FEATURE]: Terminal/Shell compatibility layer for Windows (Git Bash + PowerShell)

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Summary

Sorry I am not a native English speaker, so I use AI to assistant this issue's grammar, but guarantee it is written by human.

Model-generated shell commands are executed verbatim. On Windows hosts this
fails often: commands written for macOS/Linux or cmd.exe don't run in Git
Bash or PowerShell. Request a shell compatibility layer that transparently
repairs commands before execution, as implemented in kimix.

Problem

• Git Bash lacks commands models commonly emit (pbcopy, xclip,
  xdg-open, wget, zip, nc, pgrep/pkill, tasklist, tree, rev,
  column, gtimeout, …). Each call dies with command not found, wasting a
  tool round-trip or derailing the task.
• Windows paths and cmd syntax break Bash: backslash paths (D:\foo\bar)
  are mangled as escapes; cmd flags (/d) are misinterpreted.
• PowerShell commands often arrive structurally broken: unclosed quotes,
  here-strings, block comments, trailing comments, backtick continuations, or
  --% — any of which can swallow the runner's try/catch wrapper.

The agent has no defense: failures surface as raw shell errors and the model
must guess its way out.

Proposed solution

A deterministic pre-execution compatibility pass with two scanners:

1. Bash fixer (Git Bash)

   • Conservative scanner over executable/argument positions only (skipping
     quotes, here-docs, command substitutions); rewrites drive-absolute and
     relative backslash paths to forward slashes, preserving glob
     metacharacters.
   • Bash-function fallbacks for missing commands, built on tools Windows
     already ships: clip.exe, powershell.exe Get-Process, curl (as
     wget), /dev/tcp (as nc -z), .NET ZipFile (as zip), perl
     one-liners (tree, rev, column), start (as open/xdg-open).
     Each fallback installs only when command -v fails, with a stub-aware
     guard for Microsoft Store python3/pip3 App Execution Aliases.
   • Structured results (BashFix.command, replacements, path_changes,
     warning) so UI/logs show exactly what changed.

2. PowerShell fixer

   • Validate quoting state (normal / single / double / here-string /
     comment / block-comment); repair by appending the missing closer.
   • Append a newline after trailing comments, backtick continuations, and
     --% so the execution wrapper isn't commented out, joined, or passed
     literally to a native command.
   • Insert a $null no-op for comment-only input; return None (reject)
     when repair is unsafe rather than executing garbage.

Why not just prompt the model?

Prompting reduces but never eliminates these errors — models regress under
long contexts and mixed training data. A deterministic shim catches 100% of
covered cases at zero token cost, and its structured warnings teach the model
and user what was fixed.

Reference implementation

kimix ships this as src/kimix/tools/file/bash/{bash_fix.py, bash_tool.py, pwsh_fix.py, process_pwsh.py} (vendored mirror: bin/kimix_native/_shell_compat.py
— ~2600 lines, self-contained, stdlib-only). The vendored copy proves the
feature can be adopted with no new dependencies. Happy to contribute a port if
there is interest.