SandboxIntegrationTests.test_glob_with_directories contradicts deepagents's documented glob() contract (files only)

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [x] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs None found. Searched `langchain-ai/langchain` and `langchain-ai/deepagents` issues/PRs for `glob`, `is_dir`, `SandboxIntegrationTests`, `directories` — no existing report. ### Reproduction Steps / Example Code (Python) ```python import tempfile, os from deepagents.backends.filesystem import FilesystemBackend with tempfile.TemporaryDirectory() as d: os.makedirs(os.path.join(d, "dir1")) os.makedirs(os.path.join(d, "dir2")) with open(os.path.join(d, "file.txt"), "w") as f: f.write("content") backend = FilesystemBackend(root_dir=d, virtual_mode=True) result = backend.glob("*", "/") print(result) # Actual: # GlobResult(error=None, matches=[{'path': '/file.txt', 'is_dir': False, ...}], truncated=False) # -- dir1 and dir2 are silently absent. ### The same holds for `SandboxBackendProtocol` imple…