[Bug] File picker fails to display subdirectories and nested files

Bug Description
@ file picker does not show files inside subdirectories

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Summary:
The @ mention file picker fails to display files when navigating into subdirectories, and certain
top-level directories are missing from the picker entirely.

Environment:

• OS: Linux (Ubuntu, kernel 6.8.0)
• Shell: zsh
• Working directory: monorepo with nested subdirectories

Steps to reproduce:

1. Open Claude Code in a project root (e.g. /projects/web-project)
2. Type @ — some folders appear, but the web/ directory is missing despite existing and being readable

(drwxr-xr-x, owner matches current user)

1. Type @web — web/ still does not appear in suggestions
2. Run cd web and relaunch Claude Code
3. Type @ — subdirectory folders are now visible (e.g. node/, next/)
4. Type @node/ or select node/ from the picker — no files are listed, the picker shows nothing

Expected behavior:

• All readable directories should appear in the @ picker
• Selecting or typing into a folder should list the files inside it

Actual behavior:

• Some top-level directories are invisible in the picker (e.g. web/)
• Files inside subdirectories are never shown when navigating into them

Workaround:
Typing the full relative path manually (e.g. @node/index.js) works correctly — the file is accessible,
so this is purely a picker UI/indexing issue.

Additional notes:

• No relevant entries in .gitignore that would explain the missing directories
• Permissions are correct (drwxr-xr-x / drwxrwxr-x)
• ~/.claude/cache/ contains no file-picker index that could be manually cleared