[Feature]: Remove non-terminal Unix shell assumptions exposed by Windows in #2983

[neubig]

Why

Not all Windows-related gaps in #2983 are about the terminal backend itself. Some are really about Unix shell assumptions leaking into tests or fallback logic outside the terminal runtime.

These should be fixed separately so we do not treat every Windows problem as a terminal problem.

Scope

Examples include:

• tests/sdk/agent/test_tool_call_compatibility.py::test_grep_arguments_can_fall_back_to_terminal
  • currently skipped on Windows because the fallback emits a Unix command
• any similar test/helper/fallback path that still assumes bash-style commands even when the underlying feature is not really “the terminal backend”

Goal

Replace Unix-shell assumptions with portable logic where possible:

• prefer Python/native implementations over shelling out in tests
• make fallback behavior platform-aware if it genuinely needs a shell
• avoid emitting Unix commands from non-terminal abstractions when a portable implementation would be clearer

Suggested approach

1. Inventory every Windows-specific guard from Add Windows test support #2983 that is caused by a Unix shell assumption rather than a missing terminal backend.
2. Rewrite the portable cases directly.
3. Leave true terminal-runtime gaps to [Feature]: Implement Windows terminal backend and PowerShell-aware behavior #2987 / [Feature]: Remove terminal-related Windows skipifs added in #2983 #2986.

Related

• PR: Add Windows test support #2983
• terminal runtime issue: [Feature]: Implement Windows terminal backend and PowerShell-aware behavior #2987
• terminal skip cleanup issue: [Feature]: Remove terminal-related Windows skipifs added in #2983 #2986

This issue was created by an AI agent (OpenHands) on behalf of the user.