fix: worktree-aware minisweagent path discovery + clean up requirements check (#1248)

Salvage of PR #1246 by ChatGPT (teknium1 session), resolved against
current main which already includes #1239.

Changes:
- Add minisweagent_path.py: worktree-aware helper that finds
  mini-swe-agent/src from either the current checkout or the main
  checkout behind a git worktree
- Use the helper in tools/terminal_tool.py and mini_swe_runner.py
  instead of naive path-relative lookup that fails in worktrees
- Clean up check_terminal_requirements():
  - local: return True (no minisweagent dep, per #1239)
  - singularity/ssh: remove unnecessary minisweagent imports
  - docker/modal: use importlib.util.find_spec with clear error
- Add regression tests for worktree path discovery and tool resolution

tests/test_minisweagent_path.py

@@ -0,0 +1,34 @@
+"""Tests for minisweagent_path.py."""
+
+from pathlib import Path
+
+from minisweagent_path import discover_minisweagent_src
+
+
+def test_discover_minisweagent_src_in_current_checkout(tmp_path):
+    repo = tmp_path / "repo"
+    src = repo / "mini-swe-agent" / "src"
+    src.mkdir(parents=True)
+
+    assert discover_minisweagent_src(repo) == src.resolve()
+
+
+def test_discover_minisweagent_src_falls_back_from_worktree_to_main_checkout(tmp_path):
+    main_repo = tmp_path / "main-repo"
+    (main_repo / ".git" / "worktrees" / "wt1").mkdir(parents=True)
+    main_src = main_repo / "mini-swe-agent" / "src"
+    main_src.mkdir(parents=True)
+
+    worktree = tmp_path / "worktree"
+    worktree.mkdir()
+    (worktree / ".git").write_text(f"gitdir: {main_repo / '.git' / 'worktrees' / 'wt1'}\n", encoding="utf-8")
+    (worktree / "mini-swe-agent").mkdir()  # empty placeholder, no src/
+
+    assert discover_minisweagent_src(worktree) == main_src.resolve()
+
+
+def test_discover_minisweagent_src_returns_none_when_missing(tmp_path):
+    repo = tmp_path / "repo"
+    repo.mkdir()
+
+    assert discover_minisweagent_src(repo) is None

tests/tools/test_terminal_tool_requirements.py

@@ -0,0 +1,28 @@
+"""Tests for terminal/file tool availability in local dev environments."""
+
+import importlib
+
+from model_tools import get_tool_definitions
+
+terminal_tool_module = importlib.import_module("tools.terminal_tool")
+
+
+class TestTerminalRequirements:
+    def test_local_backend_does_not_require_minisweagent_package(self, monkeypatch):
+        monkeypatch.setattr(
+            terminal_tool_module,
+            "_get_env_config",
+            lambda: {"env_type": "local"},
+        )
+        assert terminal_tool_module.check_terminal_requirements() is True
+
+    def test_terminal_and_file_tools_resolve_for_local_backend(self, monkeypatch):
+        monkeypatch.setattr(
+            terminal_tool_module,
+            "_get_env_config",
+            lambda: {"env_type": "local"},
+        )
+        tools = get_tool_definitions(enabled_toolsets=["terminal", "file"], quiet_mode=True)
+        names = {tool["function"]["name"] for tool in tools}
+        assert "terminal" in names
+        assert {"read_file", "write_file", "patch", "search_files"}.issubset(names)