280 lines
10 KiB
Markdown
280 lines
10 KiB
Markdown
# Plan B: Browser-First Sync (Progressive Web App)
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> **AGENT INSTRUCTION — READ FIRST**
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>
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> When you complete a phase or are ready for a code review, you **must** notify the opencode session that created this plan. Use the opencode HTTP API to send a message to session `ses_225742b62ffeOSelYyCe4IPwxL`.
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>
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> **Message format:**
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> ```
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> Subject: Plan B Review Ready — Phase X Complete
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> Body:
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> - Phase completed: [e.g., Phase 1]
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> - Files touched: [list of files added/modified]
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> - Summary: [2-3 sentence description of what was implemented]
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> - Tests: [which tests were added or updated]
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> - Blockers: [any issues or decisions needed]
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> ```
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>
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> **OpenCode API Specification:**
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> ```
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> POST https://api.opencode.ai/v1/sessions/ses_225742b62ffeOSelYyCe4IPwxL/messages
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> Content-Type: application/json
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> Authorization: Bearer <OPENCODE_API_KEY>
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>
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> Request body:
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> {
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> "role": "assistant",
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> "content": "Subject: Plan B Review Ready — Phase X Complete\n\nBody:\n- Phase completed: ...\n- Files touched: ...\n- Summary: ...\n- Tests: ...\n- Blockers: ..."
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> }
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> ```
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>
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> Wait for a response before starting the next phase unless explicitly told otherwise.
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## Goal
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Extend the existing web application so it works offline, supports concurrent editing, and syncs changes when reconnected. No native client needed — works on macOS, Windows, Linux, iOS, Android via browser.
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## Architecture
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### Current State (Already Built)
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- Server: Go HTTP + SQLite + file watcher + WebSocket hub
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- Browser: Go-served HTML + embedded scripts + IndexedDB cache + `navigator.onLine` detection
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- Documents served at `/:path*` with `index.md` default
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- Real-time updates pushed via WebSocket when files change on disk
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### What We Add
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```
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Browser (existing + new):
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├── cache.js (exists) # IndexedDB: docs, content, hashes
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├── realtime.js (exists) # WebSocket, offline indicator
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├── sync.js (new) # Sync engine: queue, conflict detection, state machine
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├── editor.js (new) # ProseMirror or textarea with operational transforms
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└── sw.js (new) # Service Worker for offline serving
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Server (existing + new):
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├── internal/sync/ (new)
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│ ├── protocol.go # Browser sync protocol (simpler than Plan A)
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│ ├── queue.go # Server-side edit queue per document
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│ ├── conflict.go # Three-way merge for text
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│ └── broadcast.go # WebSocket broadcast for live collaboration
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├── internal/auth/ (new) # Sessions + WebSocket auth
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└── httpserver/ (existing)
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├── handlers.go # Add: POST /api/documents/:path, WebSocket auth
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└── websocket.go # Extend: handle edit messages
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```
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## Sync Protocol v1 (Browser)
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### Data Model
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- **Document**: `{path, content, hash, version}`
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- **Client Edit**: `{path, baseVersion, newHash, patch}` where patch = diff from base
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- **Server Ack**: `{path, version, status: accepted|conflict}`
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- **Server Broadcast**: `{type: update, path, newContent, newVersion, author}`
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### Endpoints
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```
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GET /api/documents # List all docs (cached in IndexedDB)
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GET /api/documents/:path # Get document content (cached in IndexedDB)
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POST /api/documents/:path # Save document (requires auth)
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Body: {content, baseVersion, clientHash}
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Response: {version, status, conflict?}
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WS /api/ws # WebSocket (exists, extend for auth + edits)
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Client → Server: {type: "edit", path, patch, baseVersion}
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Server → Client: {type: "ack", path, version}
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Server → Client: {type: "broadcast", path, patch, author}
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Client → Server: {type: "cursor", path, position} // Phase 2
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```
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### Protocol Flow (Online)
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```
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1. User opens /some-doc
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2. Browser fetches content, caches in IndexedDB
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3. User edits → client generates patch (diff)
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4. Client sends WS: {type: "edit", path, patch, baseVersion}
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5. Server validates: baseVersion == current version?
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- Yes: apply patch, increment version, broadcast to other clients
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- No: return conflict, client must merge
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6. Other clients receive broadcast, update editor if viewing same doc
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```
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### Protocol Flow (Offline)
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```
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1. User goes offline (detected by navigator.onLine + fetch failure)
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2. Offline banner appears
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3. User edits → changes queued in IndexedDB: `pending_edits` store
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4. User navigates → served from IndexedDB cache
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5. User comes back online
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6. Client replays queue: for each pending edit, POST to server
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7. Server responds with ack or conflict
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8. Conflicts shown in UI for user resolution
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```
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### Conflict Resolution (Text)
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- Three-way merge using diff3 algorithm
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- If auto-merge succeeds: apply silently, show subtle notification
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- If auto-merge fails: show side-by-side diff in UI
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- User chooses: keep local, keep server, or edit merged result
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- Markdown-aware: try to merge at paragraph/section boundaries
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## Browser Sync Engine
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### IndexedDB Schema
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```js
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const DB_NAME = 'mdhub';
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const DB_VERSION = 2;
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const stores = {
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documents: 'path', // {path, title, hash, version, syncedAt}
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content: 'path', // {path, content, hash, fetchedAt}
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pending_edits: 'id', // {id, path, patch, baseVersion, createdAt, retries}
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sync_state: 'key' // {key: 'lastSync', value: timestamp}
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};
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```
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### sync.js Responsibilities
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- `queueEdit(path, patch)`: Add to pending_edits, try to send immediately
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- `syncPending()`: Replay queue when online, handle acks/conflicts
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- `applyBroadcast(path, patch)`: Apply real-time update from other user
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- `detectConflict(base, local, server)`: Run diff3, return merged or null
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- `saveToIndexedDB(path, content)`: Cache for offline reading
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### Service Worker (sw.js)
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- Intercept navigation requests (`/:path*`)
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- If offline: serve from IndexedDB cache
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- If online: network first, update cache in background
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- Cache static assets (JS, CSS, fonts) for app shell
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- Enables "Add to Home Screen" PWA behavior
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### Editor
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- Start with `<textarea>` + diff generation (simple, robust)
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- Phase 2: ProseMirror for structured editing, operational transforms
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- Auto-save: debounced 2s, queues edit immediately
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- Show sync status: unsaved → saving → saved → (offline: queued)
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## Server Changes
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### 1. Auth Middleware
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```go
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// Extend existing session system
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func authMiddleware(next http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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// Check session cookie
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// Set user in context
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// For WebSocket: authenticate on connection open
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})
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}
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```
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### 2. Document Write Endpoint
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```go
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func handleDocumentSave(w http.ResponseWriter, r *http.Request) {
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path := chi.URLParam(r, "*")
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var req struct {
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Content string `json:"content"`
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BaseVersion int `json:"baseVersion"`
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ClientHash string `json:"clientHash"`
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}
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// Verify baseVersion matches current
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// If mismatch: return 409 Conflict with server version
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// If match: save to disk, update version, broadcast WS
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}
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```
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### 3. WebSocket Extension
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```go
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type WSMessage struct {
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Type string `json:"type"` // edit, ack, broadcast, cursor
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Path string `json:"path"`
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Patch string `json:"patch"` // unified diff
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BaseVersion int `json:"baseVersion"`
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Author string `json:"author"`
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}
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func (h *Hub) handleEdit(msg WSMessage, client *Client) {
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// Validate auth
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// Apply to document
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// Broadcast to other clients viewing same path
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// Send ack to sender
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}
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```
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### 4. Versioned Documents
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- Add `version` column to `documents` table (integer, auto-increment per doc)
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- Add `document_versions` table for history:
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```sql
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CREATE TABLE document_versions (
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id INTEGER PRIMARY KEY,
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path TEXT NOT NULL,
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version INTEGER NOT NULL,
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content_hash TEXT NOT NULL,
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author TEXT,
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created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
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UNIQUE(path, version)
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);
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```
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- Current content always on disk; versions are content hashes referencing `store`
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## Implementation Phases
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### Phase 1: Offline Reading (1-2 weeks)
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- [x] IndexedDB cache for documents and content (done)
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- [x] Offline indicator UI (done)
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- [x] Service Worker for offline navigation
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- [x] Cache static assets for PWA
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- [x] Show "cached" badge on offline-loaded pages
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### Phase 2: Edit + Queue (2 weeks)
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- [ ] Simple textarea editor at `/:path/edit`
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- [ ] Auto-save with debounce
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- [ ] Queue edits in IndexedDB when offline
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- [ ] Replay queue on reconnect with exponential backoff
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- [ ] Visual "sync pending" indicator
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### Phase 3: Conflict Resolution (1-2 weeks)
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- [ ] Server versioning (add `version` to documents table)
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- [ ] `POST /api/documents/:path` with version check
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- [ ] Three-way merge on client (diff3 library)
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- [ ] Conflict UI: side-by-side or inline diff
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- [ ] Auto-merge for non-overlapping changes
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### Phase 4: Real-Time Collaboration (2 weeks)
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- [ ] WebSocket edit messages
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- [ ] Operational transforms or patch-based sync
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- [ ] Presence awareness (who's editing, cursor positions)
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- [ ] Broadcast updates to all connected clients
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- [ ] Optimistic UI updates (show edit immediately, rollback on conflict)
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### Phase 5: PWA Polish (1 week)
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- [ ] Manifest.json for "Add to Home Screen"
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- [ ] App shell architecture (instant load)
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- [ ] Background sync API for reliable offline queue
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- [ ] Push notifications for mentions/comments (future)
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## Pros
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- Builds directly on existing architecture (no new binary)
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- Works everywhere with a browser (no platform-specific code)
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- Simpler auth (reuse session cookies)
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- Real-time collaboration possible
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- PWA can feel like native app
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## Cons
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- Requires internet for editing (unless Phase 2 offline queue works well)
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- Browser storage limits (~60MB+ with storage permission)
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- Can't use native editors (VS Code, etc.)
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- WebSocket reliability on mobile/bad networks
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- Conflict UX constrained by browser capabilities
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## Decision Needed
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- Do we need native editor integration (Plan A) or is browser enough?
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- Can we build Plan B first, then extract core sync for Plan A later?
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## Shared with Plan A
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Both plans eventually need:
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- Authentication/authorization (API keys vs sessions)
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- Document versioning
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- Conflict resolution algorithms
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- Content-addressed storage (already exists)
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