core/tools/file: add grep_files regex content search

Line-oriented regex search under the workspace; skip VCS/hidden/binary
and cap match count.

tests/test_tools/test_grep_files.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from plyngent.tools.file.grep_files import grep_files
+from tests.test_tools.helpers import call_sync
+
+
+def test_grep_files_basic(workspace: object) -> None:
+    assert isinstance(workspace, Path)
+    _ = (workspace / "a.py").write_text("hello world\nfoo\n", encoding="utf-8")
+    _ = (workspace / "b.py").write_text("nope\n", encoding="utf-8")
+    out = call_sync(grep_files, "hello")
+    assert "a.py:1:" in out
+    assert "hello world" in out
+    assert "b.py" not in out
+
+
+def test_grep_files_case_insensitive(workspace: object) -> None:
+    assert isinstance(workspace, Path)
+    _ = (workspace / "t.txt").write_text("Hello\n", encoding="utf-8")
+    assert "no matches" in call_sync(grep_files, "hello")
+    out = call_sync(grep_files, "hello", case_insensitive=True)
+    assert "t.txt:1:" in out
+
+
+def test_grep_files_invalid_regex(workspace: object) -> None:
+    del workspace
+    assert "invalid regex" in call_sync(grep_files, "[")
+
+
+def test_grep_files_skip_git(workspace: object) -> None:
+    assert isinstance(workspace, Path)
+    (workspace / ".git").mkdir()
+    _ = (workspace / ".git" / "x").write_text("secret\n", encoding="utf-8")
+    _ = (workspace / "ok.txt").write_text("secret\n", encoding="utf-8")
+    out = call_sync(grep_files, "secret")
+    assert "ok.txt" in out
+    assert ".git" not in out
+
+
+def test_grep_files_max_matches(workspace: object) -> None:
+    assert isinstance(workspace, Path)
+    lines = "\n".join(f"match {i}" for i in range(10))
+    _ = (workspace / "m.txt").write_text(lines + "\n", encoding="utf-8")
+    out = call_sync(grep_files, "match", max_matches=3)
+    assert "truncated" in out