fix(core): honor the gitignore \# escape when loading ignore patterns

[wangzhengzhuo05]

What

.bmignore (and project .gitignore) could not express any pattern beginning with #.

Why

Both loaders used a naive line filter that skipped every line starting with # and never
unescaped a leading backslash:

• #*# was silently dropped as a comment.
• \#*# was stored literally, and should_ignore_path() matches with fnmatch, which
  has no escape syntax — so it matched nothing.

The failure mode is silent and misleading: the pattern looks right in .bmignore and
simply never loads. It makes Emacs autosave files (#file#) impossible to ignore through
the documented gitignore-style syntax, even though the shipped defaults already cover
*~, *.swp and *.swo. As the issue notes, the matcher itself handles #*# correctly
(it fnmatches each path part) — only the loader was broken.

How

Added one small module-level helper, _parse_ignore_pattern_line(), and routed both the
.bmignore and .gitignore read loops through it:

• blank lines and comments (leading #) are still skipped;
• a line starting with \# now yields the pattern with one leading backslash stripped,
  per the gitignore rule "Put a backslash in front of the first hash for patterns that
  begin with a hash" — so \#*# loads as #*# and matches.

should_ignore_path() is unchanged, DEFAULT_IGNORE_PATTERNS is unchanged (adding a
default #*# would be a separate product decision), and no dependency was added
(no pathspec).

Tests

Three regression tests in tests/cli/test_ignore_utils.py:

• test_bmignore_escaped_hash_pattern_loads — \#*# in .bmignore loads as #*#, the
  comment line is still skipped, and should_ignore_path("notes/#note.md#") is True.
• test_bmignore_bare_hash_is_still_a_comment — a bare #*# remains a comment.
• test_gitignore_escaped_hash_pattern_loads — same escape handling for a project
  .gitignore.

$ .venv/bin/python -m pytest tests/cli/test_ignore_utils.py -q
17 passed
$ ruff check  (both files)         -> All checks passed!
$ ruff format --check (both files) -> 2 files already formatted

Mutation check

Reverting only the escape handling in _parse_ignore_pattern_line() (the \# branch
removed, everything else intact) fails exactly the two tests that guard the fix:

FAILED tests/cli/test_ignore_utils.py::test_bmignore_escaped_hash_pattern_loads
FAILED tests/cli/test_ignore_utils.py::test_gitignore_escaped_hash_pattern_loads
2 failed, 1 passed, 14 deselected

Restoring the fix → 17 passed.

Fixes #1539

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve leading whitespace before unescaping hashes

When a .gitignore contains \#foo, a valid pattern for the filename #foo, strip() removes the significant leading space and the new escape branch converts the remainder to #foo. Basic Memory therefore ignores/index-excludes the wrong file, while git check-ignore --no-index matches only #foo; Git's pattern format discards unescaped trailing spaces, not leading ones. Preserve leading characters when removing the line ending before recognizing the hash escape.

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