diff --git a/desloppify/engine/detectors/coupling.py b/desloppify/engine/detectors/coupling.py
index 4061412c0..b7c072631 100644
--- a/desloppify/engine/detectors/coupling.py
+++ b/desloppify/engine/detectors/coupling.py
@@ -56,6 +56,14 @@ def _rel_to_root(value: str, root_norm: str) -> str:
     """Return root-relative variant (best effort) for path/prefix matching."""
     if value.startswith(root_norm):
         return value[len(root_norm) :]
+    # On Windows, root_norm may be drive-rooted ("C:/project/") after
+    # Path.resolve(), while the caller still passes POSIX-rooted paths
+    # ("/project/..."). Strip the drive letter from root_norm and retry so
+    # tests and tools that mix the two shapes still match.
+    if len(root_norm) > 3 and root_norm[1:3] == ":/":
+        root_no_drive = root_norm[2:]
+        if value.startswith(root_no_drive):
+            return value[len(root_no_drive) :]
     return value.lstrip("/")
 
 
diff --git a/desloppify/engine/detectors/coverage/mapping_analysis.py b/desloppify/engine/detectors/coverage/mapping_analysis.py
index 390af6eb3..10b63db80 100644
--- a/desloppify/engine/detectors/coverage/mapping_analysis.py
+++ b/desloppify/engine/detectors/coverage/mapping_analysis.py
@@ -139,7 +139,10 @@ def _build_prod_by_module(
     project_root: str,
 ) -> dict[str, str]:
     """Build module lookup map for production files."""
-    root_str = project_root + os.sep
+    # Normalize to POSIX-style for the prefix comparison so mixed-slash inputs
+    # (Windows root + forward-slash relative segments from other tools) match.
+    root_posix = project_root.replace(os.sep, "/")
+    root_str = root_posix + "/"
     prod_by_module: dict[str, str] = {}
     ambiguous_aliases: set[str] = set()
 
@@ -154,10 +157,11 @@ def assign_alias(alias: str, prod_file: str) -> None:
         prod_by_module.pop(alias, None)
 
     for prod_file in production_files:
+        normalized_prod = prod_file.replace(os.sep, "/")
         rel_path = (
-            prod_file[len(root_str) :]
-            if prod_file.startswith(root_str)
-            else prod_file
+            normalized_prod[len(root_str) :]
+            if normalized_prod.startswith(root_str)
+            else normalized_prod
         )
         # Strip src/ prefix so src-layout projects map correctly
         # (e.g. 'src/argos_toolkit/foo.py' -> 'argos_toolkit.foo')
diff --git a/desloppify/engine/detectors/test_coverage/discovery.py b/desloppify/engine/detectors/test_coverage/discovery.py
index 32a65bc96..3f7ff6550 100644
--- a/desloppify/engine/detectors/test_coverage/discovery.py
+++ b/desloppify/engine/detectors/test_coverage/discovery.py
@@ -16,13 +16,34 @@
 
 
 def _normalize_graph_paths(graph: dict) -> dict:
-    """Normalize graph paths to relative paths."""
-    root_prefix = str(get_project_root()) + os.sep
+    """Normalize graph paths to relative paths.
 
-    def _to_rel(path: str) -> str:
-        return path[len(root_prefix) :] if path.startswith(root_prefix) else path
+    Comparison is done in POSIX form (forward slashes) so mixed-slash inputs
+    on Windows still match, but the returned keys preserve the input separator
+    convention by slicing from the original path string.
+    """
+    root_native = str(get_project_root())
+    root_posix = root_native.replace(os.sep, "/")
+    root_prefix_native = root_native + os.sep
+    root_prefix_posix = root_posix + "/"
 
-    needs_norm = any(k.startswith(root_prefix) for k in graph)
+    def _to_rel(path: str) -> str:
+        # Prefer native-form trim so callers that pass purely native paths
+        # get back native-form relatives (preserves existing contract).
+        if path.startswith(root_prefix_native):
+            return path[len(root_prefix_native) :]
+        # Fall back to POSIX-form trim for callers that pass mixed-slash paths
+        # (e.g. Windows root + forward-slash relative from cargo/npm/etc.).
+        normalized = path.replace(os.sep, "/")
+        if normalized.startswith(root_prefix_posix):
+            return normalized[len(root_prefix_posix) :]
+        return path
+
+    needs_norm = any(
+        k.startswith(root_prefix_native)
+        or k.replace(os.sep, "/").startswith(root_prefix_posix)
+        for k in graph
+    )
     if not needs_norm:
         return graph
 
@@ -44,10 +65,12 @@ def _discover_scorable_and_tests(
     extra_test_files: set[str] | None,
 ) -> tuple[set[str], set[str], set[str], int]:
     """Return (production_files, test_files, scorable_files, potential)."""
-    root_prefix = str(get_project_root()) + os.sep
+    root_posix = str(get_project_root()).replace(os.sep, "/")
+    root_prefix = root_posix + "/"
 
     def _to_rel(path: str) -> str:
-        return path[len(root_prefix) :] if path.startswith(root_prefix) else path
+        normalized = path.replace(os.sep, "/")
+        return normalized[len(root_prefix) :] if normalized.startswith(root_prefix) else normalized
 
     all_files = zone_map.all_files()
     production_files = set(zone_map.include_only(all_files, Zone.PRODUCTION, Zone.SCRIPT))
diff --git a/desloppify/engine/policy/zones.py b/desloppify/engine/policy/zones.py
index 16e524524..7e37af02a 100644
--- a/desloppify/engine/policy/zones.py
+++ b/desloppify/engine/policy/zones.py
@@ -90,6 +90,12 @@ def _match_pattern(rel_path: str, pattern: str) -> bool:
 
     See ZoneRule docstring for pattern type conventions.
     """
+    # Normalize separators so the rest of the pattern logic doesn't have to
+    # think about Windows backslashes. Patterns are documented as
+    # POSIX-style (e.g. "/tests/"); callers that pass native paths
+    # (rare, mostly in tests) should still classify correctly.
+    rel_path = rel_path.replace("\\", "/")
+    pattern = pattern.replace("\\", "/")
     basename = os.path.basename(rel_path)
 
     # Directory pattern: "/dir/" → substring on padded path
diff --git a/desloppify/languages/_framework/treesitter/imports/resolvers_backend.py b/desloppify/languages/_framework/treesitter/imports/resolvers_backend.py
index 756b4fd60..2570714d5 100644
--- a/desloppify/languages/_framework/treesitter/imports/resolvers_backend.py
+++ b/desloppify/languages/_framework/treesitter/imports/resolvers_backend.py
@@ -19,7 +19,10 @@ def resolve_go_import(import_text: str, source_file: str, scan_path: str) -> str
         return None
 
     rel_path = import_text[len(module_path) :].lstrip("/")
-    candidate_dir = os.path.join(scan_path, rel_path)
+    # The import path uses forward slashes (Go module convention); on Windows,
+    # os.path.join with a forward-slashed segment produces mixed separators.
+    # Normalize so callers get native-form paths.
+    candidate_dir = os.path.normpath(os.path.join(scan_path, rel_path))
     if os.path.isdir(candidate_dir):
         for filename in sorted(os.listdir(candidate_dir)):
             if filename.endswith(".go") and not filename.endswith("_test.go"):
@@ -44,15 +47,15 @@ def resolve_rust_import(import_text: str, source_file: str, scan_path: str) -> s
     path_parts = parts[:-1] if len(parts) > 1 else parts
     candidate = os.path.join(src_dir, *path_parts) + ".rs"
     if os.path.isfile(candidate):
-        return candidate
+        return os.path.normpath(candidate)
 
     candidate = os.path.join(src_dir, *path_parts, "mod.rs")
     if os.path.isfile(candidate):
-        return candidate
+        return os.path.normpath(candidate)
 
     candidate = os.path.join(src_dir, *parts) + ".rs"
     if os.path.isfile(candidate):
-        return candidate
+        return os.path.normpath(candidate)
     return None
 
 
@@ -70,7 +73,7 @@ def resolve_java_import(import_text: str, source_file: str, scan_path: str) -> s
     for src_root in ["src/main/java", "src", "app/src/main/java", "."]:
         candidate = os.path.join(scan_path, src_root, rel_path)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
     return None
 
 
@@ -89,7 +92,7 @@ def resolve_kotlin_import(import_text: str, source_file: str, scan_path: str) ->
         for src_root in ["src/main/kotlin", "src/main/java", "src", "app/src/main/kotlin", "."]:
             candidate = os.path.join(scan_path, src_root, rel_path)
             if os.path.isfile(candidate):
-                return candidate
+                return os.path.normpath(candidate)
     return None
 
 
@@ -101,12 +104,12 @@ def resolve_cxx_include(import_text: str, source_file: str, scan_path: str) -> s
     base = os.path.dirname(source_file)
     candidate = os.path.normpath(os.path.join(base, import_text))
     if os.path.isfile(candidate):
-        return candidate
+        return os.path.normpath(candidate)
 
     for inc_dir in ["include", "src", "."]:
         candidate = os.path.join(scan_path, inc_dir, import_text)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
     return None
 
 
@@ -122,10 +125,10 @@ def resolve_csharp_import(import_text: str, source_file: str, scan_path: str) ->
         rel_path = os.path.join(*parts[:-1], filename)
         candidate = os.path.join(scan_path, src_root, rel_path)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
         candidate = os.path.join(scan_path, src_root, filename)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
     return None
 
 
@@ -137,7 +140,7 @@ def resolve_dart_import(import_text: str, source_file: str, scan_path: str) -> s
         parts = import_text[len("package:") :].split("/", 1)
         if len(parts) < 2:
             return None
-        candidate = os.path.join(scan_path, "lib", parts[1])
+        candidate = os.path.normpath(os.path.join(scan_path, "lib", parts[1]))
         return candidate if os.path.isfile(candidate) else None
 
     base = os.path.dirname(source_file)
@@ -159,7 +162,7 @@ def resolve_scala_import(import_text: str, source_file: str, scan_path: str) ->
     for src_root in ["src/main/scala", "src", "."]:
         candidate = os.path.join(scan_path, src_root, rel_path)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
     return None
 
 
@@ -185,5 +188,5 @@ def resolve_swift_import(import_text: str, source_file: str, scan_path: str) ->
             continue
         seen.add(candidate)
         if os.path.isfile(candidate):
-            return candidate
+            return os.path.normpath(candidate)
     return None
diff --git a/desloppify/languages/_framework/treesitter/imports/resolvers_scripts.py b/desloppify/languages/_framework/treesitter/imports/resolvers_scripts.py
index d8c159249..2ad619d3c 100644
--- a/desloppify/languages/_framework/treesitter/imports/resolvers_scripts.py
+++ b/desloppify/languages/_framework/treesitter/imports/resolvers_scripts.py
@@ -173,8 +173,11 @@ def resolve_js_import(import_text: str, source_file: str, scan_path: str) -> str
 
     base = os.path.dirname(source_file)
     candidate = os.path.normpath(os.path.join(base, import_text))
+    # Concatenating "/index.js" onto a Windows path produces mixed separators
+    # ("C:\\...\\ui/index.js"); normalize each candidate so the returned path
+    # uses native separators throughout.
     for ext in ("", ".js", ".jsx", ".mjs", ".cjs", "/index.js", "/index.jsx"):
-        path = candidate + ext
+        path = os.path.normpath(candidate + ext)
         if os.path.isfile(path):
             return path
     return None
diff --git a/desloppify/languages/javascript/test_coverage.py b/desloppify/languages/javascript/test_coverage.py
index 408ec6b3c..b990f95f8 100644
--- a/desloppify/languages/javascript/test_coverage.py
+++ b/desloppify/languages/javascript/test_coverage.py
@@ -112,6 +112,9 @@ def resolve_import_spec(
 
     base = os.path.dirname(test_path)
     candidate = os.path.normpath(os.path.join(base, spec))
+    # production_files keys are POSIX-style (forward slashes). os.path.normpath
+    # produces backslashes on Windows, so normalize back to POSIX for lookup.
+    candidate = candidate.replace(os.sep, "/")
     for ext in ("", ".js", ".jsx", ".mjs", ".cjs", "/index.js", "/index.jsx"):
         path = candidate + ext
         if path in production_files:
diff --git a/desloppify/tests/commands/plan/test_triage_split_modules_direct.py b/desloppify/tests/commands/plan/test_triage_split_modules_direct.py
index c96df51b5..96ccdae0c 100644
--- a/desloppify/tests/commands/plan/test_triage_split_modules_direct.py
+++ b/desloppify/tests/commands/plan/test_triage_split_modules_direct.py
@@ -1311,10 +1311,15 @@ def test_orchestrator_pipeline_entrypoint_is_exposed() -> None:
 
 
 def test_orchestrator_pipeline_writes_exact_cli_helper(tmp_path: Path) -> None:
+    import sys
     helper = orchestrator_pipeline_mod._write_desloppify_cli_helper(tmp_path)
     text = helper.read_text(encoding="utf-8")
     assert helper.exists()
-    assert helper.stat().st_mode & 0o111
+    # POSIX exec bits don't map onto Windows file modes (Windows uses ACLs);
+    # the helper is invoked via bash/PYTHONPATH wiring rather than direct exec
+    # so missing exec bits aren't a functional regression on Windows.
+    if sys.platform != "win32":
+        assert helper.stat().st_mode & 0o111
     assert "PYTHONPATH=" in text
     assert "-m desloppify.cli" in text
 
diff --git a/desloppify/tests/commands/review/test_runner_rovodev_direct.py b/desloppify/tests/commands/review/test_runner_rovodev_direct.py
index f18f0acf5..6b30509c3 100644
--- a/desloppify/tests/commands/review/test_runner_rovodev_direct.py
+++ b/desloppify/tests/commands/review/test_runner_rovodev_direct.py
@@ -25,6 +25,11 @@ def test_rovodev_batch_command_includes_acli_rovodev_run_invocation(monkeypatch)
     monkeypatch.delenv("DESLOPPIFY_ROVODEV_OUTPUT_SCHEMA", raising=False)
     monkeypatch.delenv("DESLOPPIFY_ROVODEV_EXTRA_ARGS", raising=False)
     monkeypatch.delenv("DESLOPPIFY_ROVODEV_EXECUTABLE", raising=False)
+    # On Windows, _resolve_executable wraps in `cmd /c` when the binary isn't on
+    # PATH, and _wrap_cmd_c then collapses the list — correct production
+    # behavior, but it obscures per-arg list shape. Stub to the unwrapped form
+    # so this test verifies command construction logic cross-platform.
+    monkeypatch.setattr(runner_rovodev_mod, "_resolve_executable", lambda name: [name])
 
     cmd = runner_rovodev_mod.rovodev_batch_command(
         prompt="hello world",
@@ -50,6 +55,7 @@ def test_rovodev_batch_command_honours_env_overrides(monkeypatch) -> None:
     monkeypatch.setenv("DESLOPPIFY_ROVODEV_OUTPUT_SCHEMA", '{"type":"object"}')
     monkeypatch.setenv("DESLOPPIFY_ROVODEV_EXTRA_ARGS", "--config-override foo")
     monkeypatch.setenv("DESLOPPIFY_ROVODEV_EXECUTABLE", "acli")
+    monkeypatch.setattr(runner_rovodev_mod, "_resolve_executable", lambda name: [name])
 
     cmd = runner_rovodev_mod.rovodev_batch_command(
         prompt="prompt",
@@ -70,6 +76,7 @@ def test_rovodev_batch_command_no_yolo_opt_out(monkeypatch) -> None:
     monkeypatch.setenv("DESLOPPIFY_ROVODEV_NO_YOLO", "1")
     monkeypatch.delenv("DESLOPPIFY_ROVODEV_OUTPUT_SCHEMA", raising=False)
     monkeypatch.delenv("DESLOPPIFY_ROVODEV_EXTRA_ARGS", raising=False)
+    monkeypatch.setattr(runner_rovodev_mod, "_resolve_executable", lambda name: [name])
 
     cmd = runner_rovodev_mod.rovodev_batch_command(
         prompt="p",
diff --git a/desloppify/tests/commands/test_helpers.py b/desloppify/tests/commands/test_helpers.py
index 580f00339..ccfd09355 100644
--- a/desloppify/tests/commands/test_helpers.py
+++ b/desloppify/tests/commands/test_helpers.py
@@ -167,7 +167,8 @@ def test_state_path_from_explicit_state_arg():
     args = SimpleNamespace(state="/custom/path.json", lang=None)
     result = state_path(args)
     assert result is not None
-    assert str(result) == "/custom/path.json"
+    # Use as_posix() to normalize separators on Windows.
+    assert result.as_posix() == "/custom/path.json"
 
 
 def test_state_path_from_lang_arg():
diff --git a/desloppify/tests/commands/test_runner_modules_direct.py b/desloppify/tests/commands/test_runner_modules_direct.py
index 083885ca8..798473feb 100644
--- a/desloppify/tests/commands/test_runner_modules_direct.py
+++ b/desloppify/tests/commands/test_runner_modules_direct.py
@@ -163,6 +163,11 @@ def fake_run(cmd, **kwargs):
 
 def test_codex_batch_command_uses_sanitized_reasoning_effort(monkeypatch, tmp_path: Path) -> None:
     monkeypatch.setenv("DESLOPPIFY_CODEX_REASONING_EFFORT", "HIGH")
+    # On Windows _resolve_executable wraps unresolvable names in `cmd /c`,
+    # then _wrap_cmd_c collapses the rest of the args into one string. That's
+    # correct production behavior but obscures per-arg list shape the test
+    # asserts. Patch to the unwrapped form so this test runs cross-platform.
+    monkeypatch.setattr(codex_batch_mod, "_resolve_executable", lambda name: [name])
 
     command = codex_batch_mod.codex_batch_command(
         prompt="review prompt",
@@ -170,7 +175,6 @@ def test_codex_batch_command_uses_sanitized_reasoning_effort(monkeypatch, tmp_pa
         output_file=tmp_path / "out.json",
     )
 
-    # On Windows with .cmd wrappers, prefix may be ["cmd", "/c", "...codex.cmd"]
     assert any(c.endswith("codex") or "codex" in c for c in command[:3])
     assert "exec" in command
     assert "--ephemeral" in command
diff --git a/desloppify/tests/detectors/test_external_adapters.py b/desloppify/tests/detectors/test_external_adapters.py
index eb5aec350..d100cc518 100644
--- a/desloppify/tests/detectors/test_external_adapters.py
+++ b/desloppify/tests/detectors/test_external_adapters.py
@@ -553,6 +553,10 @@ def test_returns_none_on_timeout(self, tmp_path):
         ):
             assert detect_with_jscpd(tmp_path) is None
 
+    @pytest.mark.skipif(
+        not hasattr(__import__("os"), "getpgid"),
+        reason="os.getpgid is POSIX-only; the process-group kill path doesn't apply on Windows",
+    )
     def test_timeout_kills_jscpd_process_group(self):
         class FakeProc:
             pid = 4321
@@ -963,11 +967,13 @@ def test_returns_absolute_paths(self, tmp_path):
         assert all(p.startswith(str(tmp_path)) for p in result)
 
     def test_includes_default_non_glob_entries(self, tmp_path):
+        import os
         with patch(
             "desloppify.base.discovery.source.get_exclusions", return_value=()
         ):
             result = collect_exclude_dirs(tmp_path)
-        basenames = {p.rsplit("/", 1)[-1] for p in result}
+        # Use os.path.basename to be separator-agnostic (Windows uses \, POSIX /).
+        basenames = {os.path.basename(p) for p in result}
         assert "node_modules" in basenames
         assert "__pycache__" in basenames
         assert ".git" in basenames
@@ -983,12 +989,13 @@ def test_excludes_glob_patterns(self, tmp_path):
         assert not any("*" in p for p in result)
 
     def test_includes_runtime_exclusions(self, tmp_path):
+        import os
         with patch(
             "desloppify.base.discovery.source.get_exclusions",
             return_value=("vendor", "third_party"),
         ):
             result = collect_exclude_dirs(tmp_path)
-        basenames = {p.rsplit("/", 1)[-1] for p in result}
+        basenames = {os.path.basename(p) for p in result}
         assert "vendor" in basenames
         assert "third_party" in basenames
 
@@ -1003,10 +1010,12 @@ def test_skips_runtime_glob_exclusions(self, tmp_path):
 
     def test_deduplicates(self, tmp_path):
         """Runtime exclusion that overlaps with DEFAULT_EXCLUSIONS doesn't produce dupes."""
+        import os
         with patch(
             "desloppify.base.discovery.source.get_exclusions",
             return_value=("node_modules",),
         ):
             result = collect_exclude_dirs(tmp_path)
-        node_entries = [p for p in result if p.endswith("/node_modules")]
+        # Use basename, separator-agnostic (Windows uses \).
+        node_entries = [p for p in result if os.path.basename(p) == "node_modules"]
         assert len(node_entries) == 1
diff --git a/desloppify/tests/review/context/test_holistic_review_dimensions_and_structure.py b/desloppify/tests/review/context/test_holistic_review_dimensions_and_structure.py
index 9885e9575..04d214381 100644
--- a/desloppify/tests/review/context/test_holistic_review_dimensions_and_structure.py
+++ b/desloppify/tests/review/context/test_holistic_review_dimensions_and_structure.py
@@ -271,8 +271,10 @@ def test_writes_to_file(self, tmp_path):
         plan = generate_remediation_plan(state, "python", output_path=output)
 
         assert output.exists()
-        assert output.read_text() == plan
-        assert "Issue" in output.read_text()
+        # Plan contains unicode (middle dot, etc.) written as UTF-8; locale-default
+        # read (cp1252 on Windows) would mangle the bytes. Always read as UTF-8.
+        assert output.read_text(encoding="utf-8") == plan
+        assert "Issue" in output.read_text(encoding="utf-8")
 
     def test_lang_name_in_commands(self):
         state = _state_with_holistic_issues(
diff --git a/desloppify/tests/review/review_commands_cases.py b/desloppify/tests/review/review_commands_cases.py
index 905e0dd03..d1dc563b6 100644
--- a/desloppify/tests/review/review_commands_cases.py
+++ b/desloppify/tests/review/review_commands_cases.py
@@ -102,6 +102,17 @@ def test_import_notice_warns_and_returns_missing_dimensions(self, capsys):
 
 
 class TestCmdReviewPrepare:
+    @pytest.fixture(autouse=True)
+    def _disable_cmd_c_wrapping(self, monkeypatch):
+        """Stub _resolve_executable so Windows doesn't wrap the codex command in
+        `cmd /c ...` and _wrap_cmd_c doesn't collapse the per-arg list. The
+        per-arg shape is what fake_subprocess_run relies on (it does
+        ``cmd[cmd.index('-o') + 1]``); the wrapping is correct production
+        behavior but makes the test environment-dependent."""
+        monkeypatch.setattr(
+            runner_process_mod, "_resolve_executable", lambda name: [name]
+        )
+
     def test_do_prepare_writes_query_json(
         self, mock_lang_with_zones, empty_state, tmp_path
     ):
@@ -950,8 +961,13 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg added by the runner when
+            # prompt-via-stdin is active (always on Windows; for long prompts
+            # on Linux). Without it, the fake raises TypeError and the batch
+            # fails with exit_code=1 long before the result is examined.
+            _ = timeout, cwd, kwargs
             out_path = Path(cmd[cmd.index("-o") + 1])
             out_path.parent.mkdir(parents=True, exist_ok=True)
             payloads = {
@@ -1190,8 +1206,12 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg added by the runner when
+            # prompt-via-stdin is active (always on Windows; for long prompts
+            # on Linux). Without it the fake raises TypeError.
+            _ = capture_output, text, timeout, cwd, kwargs
             out_path = Path(cmd[cmd.index("-o") + 1])
             out_path.parent.mkdir(parents=True, exist_ok=True)
             payload = {
@@ -1309,8 +1329,12 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg added by the runner when
+            # prompt-via-stdin is active (always on Windows; for long prompts
+            # on Linux). Without it the fake raises TypeError.
+            _ = capture_output, text, timeout, cwd, kwargs
             out_path = Path(cmd[cmd.index("-o") + 1])
             out_path.parent.mkdir(parents=True, exist_ok=True)
             payload = {
@@ -1466,8 +1490,11 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg the runner passes when
+            # prompt-via-stdin is active (always on Windows).
+            _ = capture_output, text, timeout, cwd, kwargs
             # Simulate Codex occasionally returning JSON on stdout while failing
             # to write the -o output file. collect_batch_results should recover
             # from the batch log and persist the recovered raw payload.
@@ -1576,8 +1603,12 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg added by the runner when
+            # prompt-via-stdin is active (always on Windows; for long prompts
+            # on Linux). Without it the fake raises TypeError.
+            _ = capture_output, text, timeout, cwd, kwargs
             out_path = Path(cmd[cmd.index("-o") + 1])
             out_path.parent.mkdir(parents=True, exist_ok=True)
             if out_path.name == "batch-1.raw.txt":
@@ -1707,8 +1738,11 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg the runner passes when
+            # prompt-via-stdin is active (always on Windows).
+            _ = capture_output, text, timeout, cwd, kwargs
             return MagicMock(returncode=124, stdout="", stderr="timed out")
 
         lang = MagicMock()
@@ -1775,8 +1809,12 @@ def fake_subprocess_run(
             text=False,
             timeout=None,
             cwd=None,
+            **kwargs,
         ):
-            _ = capture_output, text, timeout, cwd
+            # **kwargs absorbs the ``input=`` kwarg added by the runner when
+            # prompt-via-stdin is active (always on Windows; for long prompts
+            # on Linux). Without it the fake raises TypeError.
+            _ = capture_output, text, timeout, cwd, kwargs
             out_path = Path(cmd[cmd.index("-o") + 1])
             out_path.parent.mkdir(parents=True, exist_ok=True)
             payload = {
@@ -1937,7 +1975,10 @@ def test_run_codex_batch_writes_live_status_before_completion(self, tmp_path):
         output_file = tmp_path / "out.txt"
         live_snapshot = {"text": ""}
 
-        def fake_run(_cmd, *, capture_output, text, timeout):  # noqa: ARG001
+        def fake_run(_cmd, *, capture_output, text, timeout, **kwargs):  # noqa: ARG001
+            # **kwargs absorbs the ``input=`` kwarg the runner passes when
+            # prompt-via-stdin is active (always on Windows).
+            _ = kwargs
             if log_file.exists():
                 live_snapshot["text"] = log_file.read_text()
             output_file.write_text('{"assessments": {}, "issues": []}')