docs: update FEATURES, ARCHITECTURE, and OpenAPI spec for image attachments

- FEATURES.md: document client-side optimization, thumbnails, offline support, SW caching
- ARCHITECTURE.md: add attachment data flow section (client → optimize → IDB/server → SW cache)
- openapi.yaml: add &thumb=1 query param, thumbnail FormData field, thumbnailPath in Attachment schema, attachments array in Note schema

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -49,6 +49,14 @@ For a single-user app with multiple devices:
 - If timestamps match: higher version wins
 - If both match: local version is preferred
 
+### Attachment Data Flow
+1. User drops/picks image in NoteEditor
+2. Client optimizes: resize ≤1920px, compress to WebP, generate 200px thumbnail
+3. **Online**: POST optimized + thumbnail to `/api/notes/{id}/attachments` → server saves to `data/attachments/` + DB
+4. **Offline**: store blobs in IDB `pendingAttachments` store → display via `URL.createObjectURL()` → on reconnect, sync pushes to server
+5. **Display**: NoteCard uses `&thumb=1` URL (200px WebP), editor shows full-size
+6. **SW Caching**: `CacheFirst` rule caches attachment URLs — previously-viewed images available offline
+
 ## Tech Stack Rationale
 
 ### SvelteKit
@@ -89,7 +97,7 @@ Key tables:
 - `notes` - Core note data with version tracking
 - `tags` - Unique tag names
 - `note_tags` - Many-to-many note ↔ tag
-- `attachments` - Image file metadata
+- `attachments` - Image file metadata (path + thumbnailPath)
 - `sync_log` - Sync operation history
 
 ## File Organization

docs/FEATURES.md

@@ -42,7 +42,13 @@
 - Upload images via file picker or drag-and-drop
 - Supports JPEG, PNG, GIF, WebP, SVG
 - Max file size: 10MB
-- Thumbnail previews in note cards
+- **Client-side optimization**: images resized to fit 1920×1920, compressed to WebP (~80% quality), transparent PNGs preserved
+- **Auto-generated thumbnails**: 200×200 WebP at 60% quality for fast card previews
+- Thumbnail strip on note cards (up to 3 images, "+N" badge for more)
+- Full-size images in editor, thumbnails on cards (`&thumb=1`)
+- **Offline support**: optimized blobs stored in IndexedDB, displayed via blob URLs, auto-synced on reconnect
+- Pending upload indicator on offline-queued images
+- Service worker CacheFirst caching for previously-viewed images
 - Remove attachments from editor
 
 ### Tag Organization
@@ -90,9 +96,9 @@
 ### PWA / Offline-First
 - Installable as standalone app
 - Web app manifest with icons
-- Service worker for asset caching
-- IndexedDB for local data storage
-- Background sync every 30 seconds
+- Service worker for asset caching (CacheFirst for attachments, NetworkFirst for API)
+- IndexedDB for local data storage (notes + pending attachments)
+- Background sync every 30 seconds (notes + offline attachments)
 - LWW conflict resolution for multi-device use
 - Sync status indicator (synced/syncing/offline/error)
 

docs/openapi.yaml

@@ -185,6 +185,12 @@ paths:
           in: query
           schema:
             type: string
+        - name: thumb
+          in: query
+          description: Set to "1" to return the thumbnail instead of the full image (requires attachmentId)
+          schema:
+            type: string
+            enum: ['1']
       responses:
         '200':
           description: Attachment list (without attachmentId) or file content (with attachmentId)
@@ -209,6 +215,10 @@ paths:
                   type: string
                   format: binary
                   description: Image file (max 10MB)
+                thumbnail:
+                  type: string
+                  format: binary
+                  description: Pre-generated thumbnail (WebP, ~200px)
       responses:
         '201':
           description: Attachment metadata
@@ -368,6 +378,10 @@ components:
           type: array
           items:
             type: string
+        attachments:
+          type: array
+          items:
+            $ref: '#/components/schemas/Attachment'
 
     NoteInput:
       type: object
@@ -415,6 +429,10 @@ components:
           type: string
         size:
           type: integer
+        thumbnailPath:
+          type: string
+          nullable: true
+          description: Server path to thumbnail file (null if no thumbnail)
         createdAt:
           type: string
           format: date-time