Scope

What's changed:

• Add useAutoSave composable (app/src/composables/use-auto-save.ts) — debounced (750ms) auto-save driven by edits watcher. One revision per editing session: first save of the session creates a revision, subsequent saves patch it in place until AUTO_SAVE_SNAPSHOT_INTERVAL_MINUTES (5m) of inactivity promotes the next save to a new revision. Exposes autoSaveError and resetSession; resets on currentVersion change.
• Add createRevision option to VersionsService.save() and ?createRevision=false query param on POST /versions/:id/save. When false and the version has an item, skip the activity/revision insert and merge the clean delta into the latest existing revision so the sidebar reflects accumulated edits. Snapshots revisionDelta before deepMapObjects mutates it with _user/_date metadata.
• Integrate auto-save in item.vue for versioned items via autoSaveRevision(forceNew): manual save / stale session → saveVersion(...) (creates revision); otherwise → saveVersion(..., { createRevision: false }). Manual stay/quit shortcuts for versions removed — auto-save handles it.
• Remove the now-redundant patchVersionDelta path in use-versions.ts (was a raw PATCH /versions/:id that bypassed VersionsService.save — prepareDelta, hooks, permissions). Consolidates auto-save and manual save onto a single server pipeline.
• Fix: confirmVersionExists only returns false on HTTP 404; other errors (network, 5xx) are re-thrown instead of being silently treated as "version gone".

Potential Risks / Drawbacks

• In-place revision merge uses assign({}, latestRevision.data ?? {}, cleanRevisionDelta) — shallow merge. Nested objects in the delta overwrite whole subtrees rather than deep-merging. Matches prior client-side behaviour but worth confirming for complex relational payloads.
• cleanRevisionDelta is captured via JSON.parse(JSON.stringify(...)) — any non-JSON values in the delta (Date, undefined, Map) will be lost. Current payloads are JSON so this should be fine, but sharp edge.
• Auto-save fires on every edits mutation (deep watch). Debounced at 750ms; overlapping saves guarded by an isSaving mutex. Worth monitoring for very large forms.
• Session staleness threshold is a hard-coded 5 minutes; no user-facing toggle.
• Query param parsed as req.query['createRevision'] !== 'false' — any other truthy string evaluates to true. Consistent with existing Directus patterns.

Tested Scenarios

• Versioned item: typing → one revision appears, continues accumulating changes without spawning new rows.
• Idle >5m then type → new revision created on next save.
• Switching currentVersion → session resets; next save creates a new revision.
• Manual save shortcut still creates a revision (no query flag).
• Auto-save fires only when user has version update permission and currentVersion !== null.
• Version deleted/promoted mid-session → handleVersionGone swallows the error silently; autoSaveError not set.
• Non-404 network/server errors on confirmVersionExists now surface instead of being silenced.

Review Notes / Questions

• Stacked on top of alvaro/cms-1865-discard-item-less-versions-navigate-to-collection; merge that first.
• No changeset added — should this get a minor or patch entry for the new ?createRevision query param? It's additive and defaults to current behavior.
• No new API tests covering the createRevision: false branch of VersionsService.save() (latest-revision lookup + accumulated merge). Would appreciate guidance on where those belong in api/src/services/versions.test.ts.
• AUTO_SAVE_SNAPSHOT_INTERVAL_MINUTES and AUTO_SAVE_DEBOUNCE_MS are module constants — open to moving to settings if product wants them configurable.
• Special attention on the shallow merge semantics for revisions with relational/M2A deltas.

Checklist

• Added or updated tests
• Documentation PR created here or not required
• OpenAPI package PR created here or not required

Fixes CMS-1867