Background

Sibling of #647 (closed via #717) but in a different code path: the search pipeline's source_filter parameter does plain substring matching against the chunk's source_file, with no separator normalisation. On Windows that means a caller-supplied filter like /tmp/keep/ (which a test or a user types in POSIX form) never matches a chunk whose stored source_file is \tmp\keep\policy.md — separators differ, substring fails.

Affected code

• packages/memtomem/src/memtomem/search/pipeline.py:40-44 — _match_source:

  def _match_source(filter_str: str, source_path: str) -> bool:
      """Match source_filter: glob when pattern chars present, substring otherwise."""
      if any(c in filter_str for c in ("*", "?", "[")):
          return fnmatch(source_path, filter_str)
      return filter_str in source_path

• packages/memtomem/src/memtomem/search/decay.py:111-112 — expire_chunks:

  if source_filter:
      sources = {s for s in sources if source_filter in str(s)}

Both compare a user/caller-supplied substring against a stored native-form path. Neither normalises separators on either side.

Symptom on Windows CI

FAILED packages/memtomem/tests/test_temporal_validity.py::TestValidityFilterPipelineWiring::test_and_with_source_filter
  AssertionError: assert [] == ['chunk-ok']

The test sets source_filter="/tmp/keep/" and indexes a chunk with source_file=Path("/tmp/keep/policy.md"). On Windows str(WindowsPath("/tmp/keep/policy.md")) is \tmp\keep\policy.md; the substring "/tmp/keep/" is not in "\tmp\keep\policy.md" → the filter rejects the chunk → empty result.

This is not what test_and_with_source_filter is exercising — it's exercising the AND between validity and source filter, but the test never gets a chance to assert AND-semantics because the source filter alone already rejects everything on Windows.

Why this didn't get fixed by #717

#717 normalised the trailing separator inside norm_dir_prefix (os.sep instead of a hardcoded "/"). That helper is only used by engine.py:resolve_owning_memory_dir, engine.py:memory_dir_stats, and the delete_chunks=true branch of web/routes/system.py:remove_memory_dir. Search-pipeline source_filter is a separate code path: it bypasses norm_dir_prefix and does its own ad-hoc in str(...) / fnmatch(...) matching.

norm_path itself is symmetric (write side and read side both go through Path.resolve() + NFC, so the stored chunks.source_file is in native form on every OS), so the asymmetry is purely the caller's input — they pass a separator-naive substring/glob.

Fix direction

Two options, equivalent in correctness:

A) Caller-side normalise — the MemSearchInput / CLI / API layer that accepts source_filter should normalise separators to native form before passing in (e.g. source_filter.replace("/", os.sep) when not a glob, or the equivalent for fnmatch patterns). One layer to change, but every entry point has to remember.

B) Match-side normalise (recommended) — in _match_source and expire_chunks, normalise both filter_str and source_path to a single canonical form before comparing. Mirrors PR #716's read-time .replace("\\", "/") pattern in categorize_memory_dir. One helper, all callers covered. Suggested:

def _match_source(filter_str: str, source_path: str) -> bool:
    """Match source_filter: glob when pattern chars present, substring otherwise.

    Both sides are folded to forward-slash form before comparing so a
    user-typed `/tmp/keep/` matches a Windows-stored `\\tmp\\keep\\file`
    (#NNN, sibling of #647).
    """
    norm_filter = filter_str.replace("\\", "/")
    norm_source = source_path.replace("\\", "/")
    if any(c in norm_filter for c in ("*", "?", "[")):
        return fnmatch(norm_source, norm_filter)
    return norm_filter in norm_source

The decay.py:expire_chunks site should call into the same helper (currently inlined).

Test plan

• The Windows-CI failure of test_temporal_validity::test_and_with_source_filter is the existing validation surface — should turn green once _match_source normalises.
• Add a small parametrized unit test that exercises both forward-slash and backslash inputs against both forward-slash and backslash sources, mutation-validated against a hardcoded-separator regression (per the pattern in fix(indexing): use os.sep for memory_dir prefix so Windows paths match (#647) #717's TestNormDirPrefix).
• POSIX is a no-op: .replace("\\", "/") on a POSIX path is identity.

Refs

• Windows: Path canonicalization in indexing — kind detection + memory_dir comparisons #647 — sibling (closed via fix(indexing): use os.sep for memory_dir prefix so Windows paths match (#647) #717), same bug class in engine.norm_dir_prefix
• fix(indexing): use os.sep for memory_dir prefix so Windows paths match (#647) #717 — fix pattern (os.sep for trailing separator on the prefix)
• fix(config): support Windows backslash paths in categorize_memory_dir (#316) #716 — earlier sibling (categorize_memory_dir read-time .replace("\\", "/"))
• ci: add Windows runner to CI matrix #634 — Windows + macOS CI matrix umbrella

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