Smart save (autosave) for notes

[thermcampos]

Summary

Replace the localStorage draft flow for notes with Google Docs/Notion-style autosave: whatever the user types is persisted to the server, debounced. No more client-side drafts.

This spec was settled through a grilling session; the decisions below are final.

Behavior

Lazy create

• /notes/new touches no server until the first keystroke.
• On first edit: POST /rest/notes, capture the returned id, and switch the view to edit semantics. All further edits go out as PATCH /rest/notes/{id}.
• A blank title is normalized server-side to "Untitled"; a blank body is stored as ''.

Autosave

• Scope: title + body only. URL and tags remain Save-button-only (tags create entities, URL has format validation).
• Debounce: 2s trailing with a 10s max-wait cap while typing continuously.
• Flush immediately on editor blur, component unmount, and Save click.
• Saves are serialized client-side: one in-flight save max, monotonic sequence numbers, stale responses discarded, pending edits coalesced.

Concurrency safety (future-proofing for multiple tabs/users)

• NoteRequest gains an optional lastKnownUpdate field (null = skip check, preserving contract compatibility).
• PATCH compares it to the row's last_update; mismatch → 409 CONFLICT. No new column or migration: last_update is the concurrency token.
• On 409 the client silently GETs the latest note; if the user has pending edits it reapplies local title/body on top and retries with the fresh token, otherwise it adopts the server state.
• Known limitation (accepted, out of scope): two tabs both on /notes/new typing simultaneously create two separate "Untitled" notes; lazy create has no shared id. Solving this needs cross-tab coordination (BroadcastChannel/localStorage lock) and is explicitly deferred.

Backend validation changes

• Relax the shared validator (NoteService.isNoteRequestValid) for both POST and PATCH: blank title and blank description are allowed; size caps stay.
• Title null/blank → stored as "Untitled". Description blank → stored as ''.
• No Flyway migration: notes.description stays NOT NULL (empty string satisfies it). Title is already nullable.
• The hardcoded archived = false in patchNote stays as-is (archived notes cannot be edited anyway).

Status label

• Tiny muted text directly under the Markdown editor (above the Save/Cancel row).
• States: hidden when pristine → Saving… → persistent Saved HH:MM until the next edit. No spinner.
• Errors are never shown in the label; the failed save is retried on the next attempt.

Buttons

• Save (both modes, kept): flush pending autosave (await in-flight save first; never double-write), then:
  • note exists under the hood → PATCH
  • user clicked New note and hit Save without typing → POST of a blank Untitled note
  • never both requests. Then navigate Home with refreshHome as today.
• Cancel: shown only in create mode, hidden in edit mode.
  • Create mode, pristine (no keystroke): navigate Home, touch nothing, no cache invalidation.
  • Create mode, dirty: await any in-flight save / pending create, then DELETE /rest/notes/{id}?force=true, navigate Home with refetch.
  • Edit mode: no Cancel; autosaved edits simply persist (Notion-style). No snapshot/revert machinery.

Force delete

• DELETE /rest/notes/{id} currently throws NoteNotArchivedException for non-archived notes (NoteService.deleteNote).
• Add optional query param ?force=true that skips the archived check (archived check remains the default; existing trash flow untouched). One endpoint, backward compatible.

Draft machinery removal

• Remove the localStorage draft system for notes in NoteAdd (saveDraft, applyDraft, clearDraft, draft keys draft:note:new / draft:note:edit:{id}, the "Draft restored" banner, hasUserEdited). The server is now the draft.

Home cache

• Refetch Home iff the session mutated the server: Save, dirty-Cancel (note deleted), or edit mode with autosaved changes on exit. Pristine Cancel keeps today's cache reuse (Keep Home data when add forms are canceled #86).

Test plan

• Backend unit: relaxed validation (blank title/description accepted on POST and PATCH), Untitled normalization, 409 on stale lastKnownUpdate, ?force=true delete bypassing the archive check (and default still enforced).
• Backend integration (*IntTest): patch conflict flow (stale token → 409 → refetch → retry succeeds); force-delete of a fresh note.
• Frontend: debounce/coalescing (2s trailing, 10s cap), lazy-create-on-first-keystroke and id capture, label state transitions, Save flush semantics (PATCH vs POST, never both), dirty-Cancel awaits save then force-deletes, pristine-Cancel leaves cache untouched, draft removal (no localStorage writes).

Notes

• addNote() currently discards the POST response; it must return the created note so the id can be captured.
• Manual validation lives in NoteService.isNoteRequestValid (no Bean Validation annotations on NoteRequest).
• Effective DB body limit is 2000 chars (old chk_max_length check) while app validation allows 50000; out of scope here, but worth a separate look.