fix(interface): handle Windows drive-letter paths in --workspace-file

A Windows drive letter (`C:\path\file`) has its only colon right after the
letter. `resolve_workspace_files` and `_workspace_file_dest` each called
`spec.rpartition(":")` independently and treated any colon as the
`PATH:DEST` separator, so a bare Windows path like `C:\temp\wordlist.txt`
was split into source "C" and destination "\temp\wordlist.txt" -- argument
parsing then rejected it because no file named "C" exists.

Add a shared `_split_workspace_spec` helper used by both call sites. It
detects the drive-letter case (a single-letter `raw` immediately followed
by `\` or `/` in what would be `dest`) and treats the whole spec as the
path instead, leaving the explicit `PATH:DEST` form -- including one where
PATH itself starts with a drive letter -- unaffected, since rpartition's
rightmost split there lands on the real destination separator, not the
drive letter's colon.

Fixes #1257

strix/interface/utils.py

@@ -1715,10 +1715,26 @@ def validate_config_file(config_path: str) -> Path:
 # sources, so a large file makes session bring-up slower.
 
 
+def _split_workspace_spec(spec: str) -> tuple[str, str | None]:
+    """Split ``PATH[:DEST]`` into ``(path, dest)``, ``dest`` is ``None`` if absent.
+
+    A Windows drive letter's colon (``C:\\path\\file``) is the only colon in a
+    bare path. ``rpartition`` still finds it, leaving a single-letter ``raw``
+    with the rest of the path in what would be ``dest`` -- that split is
+    detected here and rejected, so the whole spec is returned as the path.
+    """
+    raw, sep, dest = spec.rpartition(":")
+    if not sep or not dest.strip():
+        return spec, None
+    if re.fullmatch(r"[A-Za-z]", raw) and dest[:1] in ("\\", "/"):
+        return spec, None
+    return raw, dest
+
+
 def _workspace_file_dest(spec: str, source: Path) -> str:
     """Return the workspace-relative destination declared by ``spec``."""
-    _, sep, dest = spec.rpartition(":")
-    candidate = dest.strip() if sep and dest.strip() else source.name
+    _, dest = _split_workspace_spec(spec)
+    candidate = dest.strip() if dest and dest.strip() else source.name
     if candidate.startswith("/") or Path(candidate).is_absolute():
         if not candidate.startswith("/workspace/"):
             raise ValueError(
@@ -1748,8 +1764,7 @@ def resolve_workspace_files(specs: list[str] | None) -> list[dict[str, str]]:
     resolved: list[dict[str, str]] = []
     seen: dict[str, str] = {}
     for spec in specs or []:
-        raw, sep, dest = spec.rpartition(":")
-        source_text = raw if sep and dest.strip() else spec
+        source_text, _ = _split_workspace_spec(spec)
         source = Path(source_text.strip()).expanduser()
         if not source.is_file():
             raise ValueError(f"'{source}' is not an existing file")

tests/test_workspace_files.py

@@ -2,12 +2,17 @@
 
 from __future__ import annotations
 
+import sys
 from typing import TYPE_CHECKING
 
 import pytest
 
 from strix.core.inputs import build_root_task
-from strix.interface.utils import read_workspace_files, resolve_workspace_files
+from strix.interface.utils import (
+    _split_workspace_spec,
+    read_workspace_files,
+    resolve_workspace_files,
+)
 
 
 if TYPE_CHECKING:
@@ -40,6 +45,32 @@ def test_a_declared_destination_is_taken_relative_to_the_workspace(
     assert resolved[0]["workspace_path"] == "/workspace/specs/openapi.yaml"
 
 
+@pytest.mark.parametrize(
+    ("spec", "expected"),
+    [
+        (r"C:\temp\wordlist.txt", (r"C:\temp\wordlist.txt", None)),
+        ("C:/temp/wordlist.txt", ("C:/temp/wordlist.txt", None)),
+        (r"C:\temp\wordlist.txt:dest/file", (r"C:\temp\wordlist.txt", "dest/file")),
+    ],
+)
+def test_a_windows_drive_letter_is_not_mistaken_for_a_dest_separator(
+    spec: str, expected: tuple[str, str | None]
+) -> None:
+    assert _split_workspace_spec(spec) == expected
+
+
+@pytest.mark.skipif(sys.platform != "win32", reason="tmp_path is only drive-letter-shaped here")
+def test_a_bare_windows_path_resolves_end_to_end(tmp_path: Path) -> None:
+    source = tmp_path / "wordlist.txt"
+    source.write_text("admin\n", encoding="utf-8")
+
+    resolved = resolve_workspace_files([str(source)])
+
+    assert resolved == [
+        {"source_path": str(source.resolve()), "workspace_path": "/workspace/wordlist.txt"}
+    ]
+
+
 def test_a_missing_file_is_rejected(tmp_path: Path) -> None:
     with pytest.raises(ValueError, match="not an existing file"):
         resolve_workspace_files([str(tmp_path / "nope.txt")])