Merge branch 'claude/validate-broken-symlink-path' into claude/brave-hamilton-ast647

The PR is now stacked on the broken-symlink fix, which carries its own copy of
`ExistingPath` and its test; take that branch's docstring and extended test
and keep this branch's streaming test alongside.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HFhMPs6vF5zyeHDvPTvRcA

Author: claude

dandi/cli/cmd_validate.py

@@ -38,8 +38,11 @@ class TruncationNotice:
 class ExistingPath(click.Path):
     """
     Like ``click.Path(exists=True)``, but also accepting broken symbolic links,
-    such as annexed files whose content is not present, which ``dandi validate``
-    knows how to handle (see ``--missing-file-content``)
+    such as the annexed files of a DataLad dataset whose content has not been
+    fetched.  ``click.Path(exists=True)`` follows the link and rejects those as
+    nonexistent, which prevented the ``--missing-file-content`` policies
+    (``error``, ``skip``, ``only-non-data``) from ever being applied to a file
+    given directly on the command line rather than via its directory.
     """
 
     def convert(

dandi/cli/tests/test_cmd_validate.py

@@ -1044,12 +1044,21 @@ def test_validate_missing_file_content_stream(
 
 @pytest.mark.ai_generated
 def test_validate_broken_symlink_path_argument(tmp_path: Path) -> None:
-    """A broken symlink can be given directly as a path to validate."""
+    """A broken symlink can be given directly as a path to validate.
+
+    The --missing-file-content policies then apply to it just as they do when
+    the containing directory is given.
+    """
     ds = _make_dandiset_with_broken_symlinks(tmp_path)
-    r = CliRunner().invoke(validate, [str(ds / "sub-001" / "sub-001.nwb")])
+    link = ds / "sub-001" / "sub-001.nwb"
+    r = CliRunner().invoke(validate, [str(link)])
     assert r.exit_code == 1
     assert "does not exist" not in r.output
     assert "FILE_CONTENT_MISSING" in r.output
+    r = CliRunner().invoke(validate, ["--missing-file-content", "skip", str(link)])
+    assert r.exit_code == 0
+    assert "FILE_CONTENT_MISSING_SKIPPED" in r.output
+    # Paths that truly do not exist are still rejected
     r = CliRunner().invoke(validate, [str(ds / "sub-001" / "nonexistent.nwb")])
     assert r.exit_code == 2
     assert "does not exist" in r.output