Add virtual IO layer with content-addressed storage for parallel sessions

[Copilot]

In-memory virtual file system enabling isolated, parallel session file operations without disk interaction. Uses SHA-256 content addressing for automatic deduplication across sessions.

Architecture

VirtualFileSystem
├── ObjectStore (shared, lock-free reads via DashMap)
│   └── DashMap<ObjectId, Bytes>
└── sessions: DashMap<SessionId, Mutex<SessionFS>>
    └── SessionFS
        ├── files: HashMap<PathBuf, ObjectId>
        ├── snapshots: HashMap<PathBuf, Vec<ObjectId>>
        └── deleted: HashSet<PathBuf>

New types in paws_domain::virtual_fs

• ObjectId — SHA-256 content hash, analogous to git blob IDs
• ObjectStore — Thread-safe deduplicated blob store (DashMap<ObjectId, Bytes>)
• SessionFS — Per-session overlay mapping paths → ObjectId, with snapshot stack for undo
• VirtualFileSystem — Multi-session orchestrator; DashMap for cross-session concurrency, tokio::sync::Mutex per session
• SessionId — UUID-based session identifier

Usage

let vfs = Arc::new(VirtualFileSystem::new());
let sid = vfs.create_session();

vfs.with_session(&sid, |fs| {
    fs.write_utf8(Path::new("/src/main.rs"), "fn main() {}");
    fs.snapshot(Path::new("/src/main.rs"))?;
    fs.write_utf8(Path::new("/src/main.rs"), "fn main() { todo!() }");
    Ok(())
}).await?;

// Undo restores previous version
vfs.with_session(&sid, |fs| fs.undo(Path::new("/src/main.rs"))).await?;

Sessions are fully isolated — writes in one session are invisible to others. Identical content across sessions is stored once via content addressing.

Dependencies added to paws_domain

• sha2 (workspace), dashmap (workspace), bytes (workspace)

Original prompt

understand the current snapshot system and design a virtual IO layer which will allow each task to work on their own version of file in memory without having to interact with disk state of the file leveraging design like object addressing files and stuff create a clean and performant system which will allow multiple sessions to run in parallel

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[manthanabc]

The VFS seems cool at the first glance, will need to do some testing, can you map out where and how it would be integrated with the read / write /execute tool calls in paws