File Viewer: edit mode for text files (edit + save in the viewer)

[Ark0N]

Requested by an early user via the r/selfhosted thread (https://www.reddit.com/r/selfhosted/comments/1vebymy/): the File Viewer can browse and preview files, but small fixes still force a hop into the terminal (or another editor). An edit mode in the viewer closes that loop, especially from the phone: agent writes a file, you review it in the viewer, tweak two lines, save, tell the agent to continue.

Rough scope:

• Frontend: an Edit toggle on text previews in the File Viewer; textarea (or CodeMirror-light) with Save/Cancel; dirty-state guard on close. Mobile-first sizing since review-on-phone is the main use case.
• Backend: a write endpoint next to the existing read path in file-routes.ts. It must inherit the SAME confinement the reads have: realpath resolution, extension allowlist, ownership scoping in multi-user mode (canAccessOwned), and a size cap. Text files only in v1 (the preview pipeline already knows what is text).
• Safety rails: never follow symlink escapes on write, reject binary, and no creation/deletion in v1 (edit-in-place only) to keep the surface small.

Out of scope for v1: syntax highlighting beyond what the preview already does, multi-file operations, and editing inside Docker/remote overlays where the viewer serves host-side bytes only.

[Ark0N]

Shipped in v1.11.0 (aicodeman@1.11.0 on npm) via #213.

The file-preview overlay can now edit workspace text files in place. Reads for edit go through GET /api/sessions/:id/file-content?edit=1, which never truncates (the plain preview stops at 500 lines, and saving such a buffer would silently delete the rest), and saves go through PUT /api/sessions/:id/file-content.

Edit-in-place only: there is no O_CREAT anywhere in the handler, so "never create, never delete" is structural rather than a convention. Concurrency is by content hash, so a file changed on disk mid-edit returns 409 with an overwrite option instead of clobbering, and writes are atomic (temp + fsync + rename) so a crash mid-save cannot leave a half-written file.

Out of scope as discussed: creation, deletion, rename, syntax highlighting, and editing through remote SSH cases (Docker cases work via the bind mount).