fix(deepagents): match CompositeBackend.glob patterns relative to the searched path - #988

Fixes #887.

Problem

For a mounted route below the searched path, CompositeBackend.glob passed the caller's pattern to the mounted backend unchanged. The pattern is relative to the searched path, but the mount matches relative to its own root. With a route at /workspace/memories/:

• glob("memories/*.txt", "/workspace") found nothing (false negative).
• Patterns containing the mount directory with wildcards or braces (mem*/*.txt, {memories,other}/*.txt) also found nothing.

Change

New private globMount translates the pattern for each mount below the searched path:

1. A leading ** (**/*.txt, **) passes through; it absorbs the route prefix.
2. A pattern that spells out the mount directory has that prefix stripped (memories/*.txt becomes *.txt inside the mount).
3. A pattern without a separator is passed through at the mount root, exactly as before.
4. Any other pattern (mem*/*.txt, {a,b}/*.txt): list the mount with ** and match each file's path relative to the searched path with micromatch, using the options the backends use (dot: true).

Cases 1 and 2 avoid listing the whole mount. Case 4 does list it, which can be costly for a large mount.

Added a patch changeset for deepagents.

Not changed

Case 3 keeps an existing behavior: a name pattern such as *.md searched from a directory above a mount is still applied at the mount's root, so glob("*.md", "/") finds /memories/notes.md. An existing test (should work with FilesystemBackend as default and StoreBackend route) pins that. #887 calls it a false positive. I left it alone because changing it could break agents that rely on it. If you want standard glob semantics there, it is a one-line change to case 3, but it needs the test updated. I'd like a maintainer to decide.

Also not covered: when the searched path is inside a route, mounts nested inside that route are not fanned out to.

Tests

Five new tests under CompositeBackend.glob with a mount below the searched path. Four fail on the old implementation and pass now; the fifth (search path inside the mount) pins existing behavior and passes on both. libs/deepagents unit tests: 1700 passed, 1 skipped. oxlint and oxfmt --check are clean.

Related: #886 (ls, #987) is a separate PR.

Authored by Mihir