Ability to mount different filesystem at specific paths

[izziaraffaele]

Add support for mounting multiple filesystem backends at specific paths within a single virtual filesystem. This would allow combining read-only and read-write filesystems (e.g. knowledge bases, shared assets, and agent workspaces) into a unified namespace.

Ideal usage

// default in memory fs
const fs = new InMemoryFS();

// mount shared readonly data
fs.mount('/mnt/knowledge', new OverlayFs({ root: "/path/to/read-only-knowledge" }))
fs.mount('/mnt/skills', new OverlayFs({ root: "/path/to/read-only-skills" }))

// mount agent workspace
fs.mount('/home/agent', new ReadWriteFs({ root: "/path/to/workspace" }))

const env = new Bash({ fs, cwd: overlay.getMountPoint() });

[cramforce]

Please explain the real world use-case. Looks cool

[izziaraffaele]

In general, this gives you much more control by decoupling the host filesystem structure from the sandbox filesystem structure. Mounting volumes is a well-established pattern in Docker, Unix, and storage libraries like unstorage.

For AI agents running just-bash, this enables:

• Shared reference data: mount documentation or code examples from a common location across multiple agent instances
• Isolated workspaces: each agent gets its own directory while sharing common resources
• Mixed persistence: Combine different backends like AgentFS for SQLite-backed storage, OverlayFs for copy-on-write, and InMemoryFs for scratch space
• Centralized tooling - Mount shared Claude skills, commands and settings to multiple agents without duplications

For example, an AI coding assistant with read-only access to documentation and read-write access to the project:

const fs = new MountableFs({ base: new InMemoryFs() });

// Agent can read but not modify reference materials
fs.mount("/docs", new OverlayFs({ root: "/shared/api-docs", readOnly: true }));
fs.mount("/examples", new OverlayFs({ root: "/shared/code-examples", readOnly: true }));

// Agent can modify the user's project
fs.mount("/project", new ReadWriteFs({ root: "/home/user/my-app" }));

const bash = new Bash({ fs, cwd: "/project" });

// Agent can now:
// - Read docs: cat /docs/api-reference.md
// - Copy examples: cp /examples/auth-template.ts ./src/auth.ts
// - Edit project files: echo "..." > ./src/index.ts

The agent sees one unified filesystem but each path can have different backends and capabilities.