Muschel and dvergr integration

Geschichte can be the filesystem rather than a repository hidden behind one.

Datahike/Konserve repository
          ↓
geschichte.fs
          ↓
muschel.fs.geschichte / MountFS
          ├── shell builtins
          ├── integrated `git`
          ├── SCI slurp/spit/require
          └── structured agent tools and app serving

Muschel's Geschichte adapter deliberately returns no physical path. Its Git builtin discovers mounted repositories and executes Geschichte's shared command engine directly. A dvergr room owns a persistent Geschichte store; a room fork owns a structurally shared Datahike workspace branch. Merge publishes and advances the parent, while discard deletes the child branch.

No .git directory or materialized checkout is required for normal sandbox work. Native compilers and external processes are the exception: they need an explicit, short-lived projection capability that materializes a snapshot, executes inside an OS sandbox, hashes/imports changes, and deletes the projection. Without that capability Muschel fails closed instead of falling back to the daemon's cwd.

Network Git is also host-injected. The standalone JVM CLI supplies HTTP/SSH transports; embedded sandboxes must provide a transport constrained by their domain, credential, and process policy.