feat(wasm): host-backed filesystem for the wasm bindings - #2275
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`new Bash({ fs })` runs scripts directly against storage the embedder
owns — a Durable Object, OPFS, IndexedDB — instead of the in-memory VFS.
Nothing is copied in or diffed back out: every read and write during a
run is a call into the host object, so there is no workspace-size ceiling
beyond the host's own and no lost-update window between runs.
The bridge implements `FsBackend` and wraps it in `PosixFs`, so hosts
supply raw storage (seven required methods, validated at construction)
and inherit POSIX semantics. `append`, `copy`, and `rename` are
synthesized when omitted, `chmod` is accepted and ignored so `chmod +x`
works against hosts with no permission model, and host errors carrying a
`code` map onto the matching `io::ErrorKind` so builtins that branch on
kind behave as they do over the built-in VFS.
Host calls may return promises, so a host filesystem implies `execute()`;
`executeSync` reports the suspension rather than blocking, and `files` is
rejected alongside `fs` because seeding cannot complete synchronously.
A host that answers `undefined` is broken, and reading that as "missing" turns every existence probe into a silent miss — a redirect reports the workspace as gone rather than reporting the host. Fail with a message that names the contract instead. Also documents the host filesystem as TM-FS-017: it widens the sandbox to whatever the embedder's object exposes, and its bytes live outside the VFS quotas, so scoping and storage limits are the embedder's.
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| Status | Name | Latest Commit | Preview URL | Updated (UTC) |
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What changed
new Bash({ fs })in the wasm bindings now runs scripts directly against embedder-owned storage such as a Durable Object, IndexedDB, or OPFS. Reads and writes stay live; no workspace copy or write-back diff is required.Hosts implement seven required raw-storage methods, validated at construction.
PosixFssupplies parent, directory, and symlink semantics. Optional append/copy/rename operations have fallbacks, host POSIX error codes map to matching I/O kinds, and malformed host responses fail explicitly.The async contract is enforced: host-backed filesystems require
execute(), andfilescannot be combined withfs.Why
Embedders previously had to copy their storage into the in-memory VFS before every run and diff it back afterward. That was O(workspace), text-oriented, and exposed a lost-update window. The new adapter lets Bashkit operate on the embedder's authoritative bytes.
Before / After
Before: scripts only saw Bashkit's in-memory VFS; external storage required seeding and write-back.
After:
The wasm integration suite proves redirects, reads, text tools, directories, copy/move fallbacks, error mapping, invalid host responses, async suspension, and constructor validation against an always-async fake host.
Risk
fsis supplied.ENOSYSfor symlink operations.Checklist