Context

Several backends now retain per-file versions and support version-pinned reads through the observer (revision_for):

• S3 (versioned buckets): reads pass VersionId; every read records fingerprint/revision (ETag/VersionId)
• GridFS (feat(gridfs): MongoDB GridFS backend with native revisions and server-side find #566): every write uploads a new revision and keeps old ones; pinned reads fetch by file _id; mv moves the whole revision history
• GDrive / OneDrive: version-pinned reads via native version APIs

But pinning is only reachable through snapshot time-travel. There is no user-facing surface for versions, and the semantics of operating while pinned to a specific version are undefined.

Questions to settle

1. Browsing: how does an agent list a file's versions? A versions <path> builtin? A synthetic view (e.g. .versions/ folder)? Must work uniformly across backends whose version tokens differ (VersionId string vs ObjectId vs Drive revision id).
2. Addressing: how is a specific version spelled in a command? cat file@<rev>? A flag? Interaction with globbing and PathSpec.
3. Semantics while pinned: if a session/mount is resolved to specific versioned files (restored snapshot):
   • what does a write do — branch from the pinned version, fail read-only, or write-latest with a warning?
   • what do ls/find/stat show — the pinned version's size/mtime or latest?
   • what does rm mean — currently GridFS/S3 delete all versions, which breaks other snapshots pinned to them
4. Retention: GridFS now accumulates revisions on every write with no pruning knob. Do we want a per-resource retention policy (keep N / keep for T / keep all), and should rm's delete-all-revisions behavior be configurable to a soft delete (delete-marker style, like S3 versioned buckets)?
5. Non-versioned backends: what do the same surfaces do on backends without version retention (disk, redis, hf buckets are non-versioned by design) — error, empty list, or emulation?

Related

• PR feat(gridfs): MongoDB GridFS backend with native revisions and server-side find #566 (GridFS backend: revisions + pinned reads)
• feat(gdrive): read/write Drive backend, gws CLI, fake Workspace server, integ targets #549 (gdrive versions)
• Deliberate find -mtime no-op / dir-mtime design discussion from Fix latent type-safety and lifecycle bugs #528 follow-ups