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+# Bookhoard Device Authentication & Sync Implementation Plan
+
+## Executive Summary
+
+**Current Problem:**
+- OPDS routes are publicly accessible (security vulnerability)
+- Kobo sync uses Bearer tokens but Kobo firmware can't send them (broken)
+- KOReader documentation is incorrect about Basic Auth
+- No clear authentication strategy for different device types
+- Sidecar implementation exists but isn't integrated
+
+**Vision:**
+Transform Bookhoard into a comprehensive Kindle-replacement ecosystem with seamless device sync, supporting both Kobo (native) and KOReader (via plugin) with full functionality including progress, highlights, notes, and bookmarks.
+
+---
+
+## 1. Current State Analysis
+
+### 1.1 Authentication Landscape
+
+**Existing Infrastructure:**
+```go
+// DeviceAuthMiddleware - Currently only supports Bearer tokens
+// File: internal/middleware/device_auth.go:37-108
+func (m *DeviceAuthMiddleware) Authenticate(next echo.HandlerFunc) echo.HandlerFunc {
+    // Only checks Authorization: Bearer {token}
+    // Validates against devices.auth_token
+}
+```
+
+**Routes Using Device Auth:**
+- `/api/sync/kobo/*` - Kobo sync endpoints
+- `/api/sync/koreader/*` - KOReader sync endpoints  
+- `/opds/devices/*` - OPDS catalog (currently NOT protected, needs auth)
+
+**Database Schema:**
+```sql
+-- devices table already has device_identifier field
+-- Can store serial numbers for Kobo devices
+```
+
+### 1.2 Kobo Integration Status
+
+**What's Broken:**
+- Kobo sends `Authorization: Bearer {kobo-store-token}` (wrong token)
+- Kobo sends `x-kobo-device: {"SerialNumber":"N123..."}` (what we need to use)
+- Current middleware rejects Kobo requests because token doesn't match
+
+**What's Working:**
+- Kobo sync handler implementation exists
+- Endpoints registered: `/api/sync/kobo/markup`, `/bookmark`, `/v1/initialization`, etc.
+- Can sync progress, highlights, notes, bookmarks once auth works
+
+### 1.3 KOReader Integration Status
+
+**What's Broken:**
+- Documentation says use "Basic Auth" - this is WRONG
+- KOReader doesn't support custom headers natively for sync
+- Bearer token can't be sent via standard KOReader settings
+
+**What's Working:**
+- KOReader sync handler supports full feature set
+- Can sync: progress, bookmarks, highlights, notes, library metadata
+- Plugin architecture exists but no Bookhoard plugin yet
+
+### 1.4 OPDS Status
+
+**Current:**
+- Routes registered in `internal/router/opds.go:11-12`
+- **NOT using DeviceAuthMiddleware** (security hole)
+- Publicly accessible - anyone can enumerate device UUIDs
+
+**Required:**
+- Must require authentication
+- Needs to work with both Kobo (serial) and KOReader (Bearer token)
+
+---
+
+## 2. User Priorities (Ranked)
+
+### Priority 1: Functionality First
+**User Quote:** "I want a Kindle system replacement, otherwise I could just use Booklore or KOReader"
+
+**Requirements:**
+- ✅ Full sync: progress, highlights, notes, bookmarks
+- ✅ Works on both Kobo and KOReader
+- ✅ Seamless user experience
+- ✅ OPDS for wireless book delivery
+- ✅ Two-way sync (device ↔ server)
+
+### Priority 2: Security Second (with documentation)
+**User Quote:** "This is a self-hosted app so as long as the user is aware of the security implications in the documentation it should be fine"
+
+**Acceptable Trade-offs:**
+- Serial-based auth for Kobo (less secure but easier)
+- Security risks documented clearly
+- Token-based for KOReader (more secure)
+- Users responsible for network security (VPN, etc.)
+
+### Priority 3: Simple Setup
+**Goal:** Minimal friction for users
+
+**Kobo Experience:**
+- Enter serial number during registration
+- One line in `Kobo eReader.conf`
+- No token management
+- Works immediately
+
+**KOReader Experience:**
+- Copy plugin files
+- Enter server URL and token
+- One-time setup
+- Background sync works automatically
+
+---
+
+## 3. Target State
+
+### 3.1 Unified Authentication Architecture
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                  DeviceAuthMiddleware                       │
+│  Enhanced to support multiple auth methods:                 │
+│                                                             │
+│  1. Authorization: Bearer {token}                          │
+│     → Lookup device by auth_token                          │
+│     → Used by: KOReader, OPDS apps                         │
+│                                                             │
+│  2. X-Kobo-Device: {"SerialNumber":"N123..."}              │
+│     → Extract serial from JSON                             │
+│     → Lookup device by device_identifier                   │
+│     → Used by: Kobo e-readers                              │
+│                                                             │
+│  Both paths result in: device context set in echo.Context   │
+└─────────────────────────────────────────────────────────────┘
+```
+
+### 3.2 Feature Matrix
+
+| Feature | Kobo (Native) | KOReader (Plugin) |
+|---------|---------------|-------------------|
+| **Progress Sync** | ✅ Automatic | ✅ Automatic |
+| **Highlights** | ✅ Native support | ✅ Via plugin API |
+| **Bookmarks** | ✅ Native support | ✅ Via plugin API |
+| **Notes** | ✅ Native support | ✅ Via plugin API |
+| **OPDS** | ✅ Via NickelMenu | ✅ Native OPDS support |
+| **Setup Complexity** | Low (1 config line) | Medium (plugin install) |
+| **Auth Method** | Serial number | Bearer token |
+| **Security** | Medium (documented) | High |
+
+### 3.3 User Flows
+
+**Kobo User Journey:**
+1. Install NickelMenu (one-time, jailbreak)
+2. Open Bookhoard web UI
+3. Register device → enter serial number (from Settings)
+4. Approve device
+5. Edit `Kobo eReader.conf` → add sync URL
+6. Read books → automatic sync
+7. Access OPDS via NickelMenu
+
+**KOReader User Journey:**
+1. Install KOReader on device
+2. Open Bookhoard web UI
+3. Register device → copy auth token
+4. Approve device
+5. Install Bookhoard plugin → paste token
+6. Configure sync settings
+7. Read books → automatic sync
+8. Add OPDS catalog → browse library
+
+---
+
+## 4. Implementation Plan
+
+### Phase 1: Enhanced Authentication (Week 1)
+**Goal:** Make auth work for both Kobo and KOReader
+
+**Tasks:**
+
+1. **Update DeviceAuthMiddleware** (`internal/middleware/device_auth.go`)
+   - [ ] Try Bearer token lookup first (existing behavior)
+   - [ ] If no Bearer token, check for `x-kobo-device` header
+   - [ ] Parse JSON to extract `SerialNumber` field
+   - [ ] Query database: `GetDeviceByDeviceIdentifier(serial)`
+   - [ ] Set device context on successful auth
+   - [ ] Return 401 if both methods fail
+
+2. **Add Database Query** (`internal/database/queries/devices.sql`)
+   - [ ] Add query: `GetDeviceByDeviceIdentifier`
+   - [ ] Ensure index exists on `device_identifier` column
+
+3. **Update Device Registration UI** (`templates/devices.templ`)
+   - [ ] Add device type selector (Kobo/KOReader)
+   - [ ] Show serial number field for Kobo (required)
+   - [ ] Show serial number field for KOReader (optional, for fallback)
+   - [ ] Generate/display auth token after approval (for KOReader)
+
+4. **Apply Middleware to OPDS** (`internal/router/opds.go`)
+   - [ ] Add `DeviceAuthMiddleware` to all `/opds/devices/*` routes
+   - [ ] Update comments to reflect auth requirements
+
+**Testing:**
+- Kobo device sync with serial auth
+- KOReader sync with Bearer token auth
+- OPDS access with both auth methods
+
+---
+
+### Phase 2: Kobo Integration (Week 1-2)
+**Goal:** Seamless Kobo experience with serial-based auth
+
+**Tasks:**
+
+1. **Kobo Setup Documentation** (`docs/user/devices/kobo-setup.md`)
+   - [ ] Revise to reflect serial-based auth (not username/password)
+   - [ ] Step-by-step guide for finding serial number
+   - [ ] NickelMenu configuration for sync
+   - [ ] Security warning about serial-based auth
+   - [ ] Network security recommendations (VPN, local network)
+
+2. **Kobo Sync Validation** (`cmd/server/tests/kobo_test.go`)
+   - [ ] Update tests to use serial auth
+   - [ ] Test sync endpoints with `x-kobo-device` header
+   - [ ] Verify all features work: progress, highlights, bookmarks, notes
+
+3. **Kobo OPDS Integration**
+   - [ ] Document OPDS URL format
+   - [ ] Test OPDS browsing with serial auth
+   - [ ] Test book downloads
+
+**Success Criteria:**
+- New Kobo device registered and syncing within 5 minutes
+- All sync features working without token management
+- Security implications clearly documented
+
+---
+
+### Phase 3: KOReader Plugin Development (Week 2-4)
+**Goal:** Full-featured KOReader plugin with Bearer token auth
+
+**Tasks:**
+
+1. **Plugin Architecture**
+   - [ ] Create `koreader-plugin/bookhoard.koplugin/` directory
+   - [ ] Implement `_meta.lua` (plugin metadata)
+   - [ ] Implement `main.lua` (entry point)
+   
+2. **Core Plugin Features**
+   - [ ] Settings UI: server URL, auth token, sync options
+   - [ ] HTTP client with Bearer token authentication
+   - [ ] Auto-sync on events:
+     - Page turn (configurable: every N pages)
+     - Bookmark added/deleted
+     - Highlight created/deleted
+     - Note added/edited
+   - [ ] Manual sync button in KOReader menu
+   - [ ] Sync status indicator
+   - [ ] Error handling and retry logic
+
+3. **Plugin API Integration**
+   - [ ] Call `/api/sync/koreader/progress` with reading position
+   - [ ] Call `/api/sync/koreader/bookmarks` with annotations
+   - [ ] Call `/api/sync/koreader/metadata` to get server-side progress
+   - [ ] Handle conflicts (server vs local progress)
+
+4. **Plugin Documentation**
+   - [ ] Installation guide (copy files, restart KOReader)
+   - [ ] Configuration guide (get token from Bookhoard UI)
+   - [ ] Usage instructions
+   - [ ] Troubleshooting guide
+
+**Success Criteria:**
+- Plugin installed and configured in under 10 minutes
+- Background sync works transparently
+- All annotation types sync properly
+- No Lua errors or crashes
+
+---
+
+### Phase 4: OPDS Security & Integration (Week 2-3)
+**Goal:** Secure OPDS with unified device authentication
+
+**Tasks:**
+
+1. **Secure OPDS Routes** (`internal/router/opds.go`)
+   - [ ] Apply `DeviceAuthMiddleware` to all OPDS endpoints
+   - [ ] Ensure auth works with both serial and Bearer methods
+   - [ ] Update router comments
+
+2. **Kobo OPDS Access**
+   - [ ] Document OPDS URL with device ID
+   - [ ] Test with NickelMenu OPDS browser
+   - [ ] Test book downloads
+
+3. **KOReader OPDS Access**
+   - [ ] Works natively via KOReader's OPDS support
+   - [ ] Uses Bearer token in header
+   - [ ] Document catalog URL format
+
+4. **Test Coverage** (`cmd/server/tests/opds_test.go`)
+   - [ ] Test unauthenticated access → expect 401
+   - [ ] Test with valid Bearer token → expect 200
+   - [ ] Test with valid serial header → expect 200
+   - [ ] Test book download with auth
+
+---
+
+### Phase 5: Testing & Documentation (Week 4)
+**Goal:** Production-ready release with comprehensive docs
+
+**Tasks:**
+
+1. **End-to-End Testing**
+   - [ ] Fresh Kobo setup: register → sync → highlights → OPDS
+   - [ ] Fresh KOReader setup: install plugin → sync → highlights → OPDS
+   - [ ] Cross-device sync: Kobo ↔ KOReader same book
+   - [ ] Offline scenarios and conflict resolution
+   - [ ] Error handling and recovery
+
+2. **Security Documentation**
+   - [ ] Security implications page
+   - [ ] Network security recommendations
+   - [ ] Comparison: Bearer vs Serial auth
+   - [ ] Threat model for self-hosted users
+
+3. **User Documentation**
+   - [ ] Quick start guide (Kobo)
+   - [ ] Quick start guide (KOReader)
+   - [ ] Feature comparison table
+   - [ ] FAQ and troubleshooting
+
+4. **Release Preparation**
+   - [ ] Version bump
+   - [ ] Changelog
+   - [ ] Migration guide (if needed)
+
+---
+
+## 5. Technical Decisions
+
+### 5.1 Why Serial-Based Auth for Kobo?
+
+**Pros:**
+- No token management required
+- Works with unmodified Kobo firmware
+- Single configuration line
+- User can't lose/forget credentials
+
+**Cons:**
+- Serial numbers are somewhat predictable
+- No token rotation possible
+- If leaked, can't be revoked (must delete device)
+
+**Mitigations:**
+- Document security risks
+- Recommend VPN for remote access
+- Use HTTPS (reverse proxy)
+- Acceptable for self-hosted personal use
+
+### 5.2 Why Bearer Token for KOReader?
+
+**Pros:**
+- Cryptographically secure
+- Can be revoked/regenerated
+- Standard authentication method
+- Works with KOReader plugin architecture
+
+**Cons:**
+- Requires plugin (can't use native settings)
+- Token must be copy-pasted during setup
+- User must manage token
+
+**Trade-off Accepted:**
+More secure but requires plugin installation. Justified because KOReader users are typically more technical and willing to install plugins.
+
+### 5.3 Why Not Use Kobo's Token?
+
+Kobo sends `Authorization: Bearer {kobo-store-token}` which is:
+- Managed by Kobo (not under our control)
+- May rotate/expire without warning
+- Only valid for Kobo's servers
+- Doesn't identify the device in our system
+
+**Decision:** Parse the `x-kobo-device` header for serial number instead.
+
+---
+
+## 6. Files to Modify
+
+### Core Authentication
+- `internal/middleware/device_auth.go` - Enhance with serial support
+- `internal/database/queries/devices.sql` - Add serial lookup query
+- `internal/router/opds.go` - Apply middleware
+
+### Device Management
+- `templates/devices.templ` - Update registration form
+- `internal/handlers/devices.go` - Handle serial input
+
+### Testing
+- `cmd/server/tests/kobo_test.go` - Update for serial auth
+- `cmd/server/tests/opds_test.go` - Add auth tests
+- `cmd/server/tests/test_helpers.go` - Add serial auth helpers
+
+### Documentation
+- `docs/user/devices/kobo-setup.md` - Rewrite for serial auth
+- `docs/user/devices/koreader-setup.md` - Update for Bearer token
+- `docs/user/security.md` - New security implications doc
+- `koreader-plugin/README.md` - Plugin documentation
+
+### New Files
+- `koreader-plugin/bookhoard.koplugin/_meta.lua` - Plugin metadata
+- `koreader-plugin/bookhoard.koplugin/main.lua` - Plugin implementation
+- `docs/user/quickstart-kobo.md` - Quick start guide
+- `docs/user/quickstart-koreader.md` - Quick start guide
+
+---
+
+## 7. Success Metrics
+
+**Functionality:**
+- ✅ Kobo syncs progress, highlights, notes, bookmarks automatically
+- ✅ KOReader syncs same features via plugin
+- ✅ OPDS works on both platforms
+- ✅ Cross-device sync works (read on Kobo, continue on KOReader)
+
+**Usability:**
+- ✅ Kobo setup time: < 5 minutes
+- ✅ KOReader setup time: < 10 minutes
+- ✅ No token management for Kobo users
+- ✅ Clear documentation with security warnings
+
+**Security:**
+- ✅ OPDS no longer publicly accessible
+- ✅ Auth required for all sync endpoints
+- ✅ Security implications documented
+- ✅ Network security recommendations provided
+
+---
+
+## 8. Future Enhancements (Out of Scope)
+
+- Auto-discovery of devices on network
+- QR code setup for mobile devices
+- Background sync service (no plugin needed)
+- Readwise/Joplin integration
+- Calibre integration
+- Mobile apps (iOS/Android)
+
+---
+
+## 9. Decisions Made (User Input)
+
+Based on user feedback, the following decisions have been finalized:
+
+### 9.1 KOReader Sync Trigger
+**Decision:** Configurable with multiple options
+- **Auto-sync**: Every N pages (configurable, default every 10 pages)
+- **Auto-sync**: Every N minutes (configurable, default every 5 minutes)
+- **Manual sync**: Always available via menu
+- **Event-triggered**: On bookmark/highlight/note creation (immediate)
+
+**Rationale:** User wants automatic sync for convenience but manual fallback for control.
+
+### 9.2 Plugin Distribution
+**Decision:** Separate repository under Bookhoard organization
+- Repository: `github.com/bookhoard/koreader-plugin`
+- Licensed under same terms as Bookhoard
+- Versioned independently
+- Referenced in main Bookhoard documentation
+
+**Rationale:** Clean separation of concerns, easier plugin-specific issues/PRs.
+
+### 9.3 Kobo Authentication
+**Decision:** Serial number ONLY
+- No Bearer token fallback for Kobo
+- Serial entered during device registration
+- Stored in `devices.device_identifier`
+
+**Rationale:** Simplest user experience, one auth method per platform.
+
+### 9.4 Conflict Resolution
+**Decision:** Use existing codebase strategy
+- Already implemented in `internal/handlers/koreader.go`
+- Uses timestamp-based last-write-wins
+- Device priority can be configured per-device
+
+**Rationale:** Don't reinvent the wheel, existing implementation is sufficient.
+
+### 9.5 Implementation Order
+**Decision:** Parallel implementation with separate sections
+- Phase 2a: Kobo Integration
+- Phase 2b: KOReader Plugin (runs concurrently)
+- Separate milestones and deliverables
+- Can ship Kobo support before plugin is ready
+
+**Rationale:** Faster time-to-market for Kobo users, plugin can follow.
+
+---
+
+## 10. Historical Context & Conversation Summary
+
+### Why This Plan Exists
+
+This implementation plan emerged from a detailed analysis of the current authentication and sync architecture. Key discoveries from codebase review:
+
+#### The Authentication Problem
+
+**Original Issue:** The plan started with `@fix-opds-device-authentication.md` which identified:
+- OPDS routes were publicly accessible (security vulnerability)
+- Test `GetDeviceCatalog_WithoutDeviceAuth` expected 401 but got 404
+- DeviceAuthMiddleware was already applied to OPDS routes, but tests were failing
+
+**Root Cause Discovery:** 
+- Kobo devices send `Authorization: Bearer {kobo-store-token}` (Kobo's store token, not Bookhoard's)
+- Kobo also sends `x-kobo-device: {"SerialNumber":"N123..."}` header
+- The middleware was rejecting requests because the Bearer token didn't match `devices.auth_token`
+- Kobo cannot send custom Bearer tokens through `eReader.conf`
+
+#### The Sidecar File Red Herring
+
+**Initial Thought:** Use `.bookhoard.json` sidecar file to pass device tokens to Kobo
+
+**Problem Discovered:** 
+- Sidecar handler exists (`internal/handlers/sidecar.go`) but routes are NOT registered
+- Kobo firmware is locked down - cannot read custom config files
+- No plugin architecture on Kobo (unlike KOReader)
+- Would require Kobo firmware modification (impossible for most users)
+
+**Decision:** Abandon sidecar approach, use serial-based auth instead
+
+#### KOReader Documentation Bug
+
+**Original Documentation:** Claimed KOReader uses "Basic Auth" with username/password
+
+**Reality:** 
+- KOReader sync sends `Authorization: Bearer {token}` to sync servers
+- The official KOReader sync protocol uses MD5 hashed passwords
+- Bookhoard's implementation expects Bearer tokens in `DeviceAuthMiddleware`
+- KOReader cannot send custom headers through native settings
+
+**Solution:** Create KOReader plugin that can send proper Bearer tokens
+
+#### Booklore Analysis
+
+**Investigation:** Analyzed how Booklore handles Kobo authentication
+
+**Booklore Approach:**
+- Token embedded in URL path: `/api/kobo/{token}/...`
+- Works but token appears in logs
+- One token per user (not per device)
+- OPDS uses separate Basic Auth
+
+**Decision:** Don't copy Booklore - less secure. Use device-specific auth with proper tokens for KOReader.
+
+#### Plugin Feasibility Research
+
+**Concern:** Is KOReader a "moving target" for plugin development?
+
+**Findings:**
+- UI plugins are unstable (Issue #13942) - frequent breaking changes
+- Backend/sync plugins (like Wallabag) are stable
+- Wallabag2 plugin has minimal updates over years
+- HTTP client APIs don't change often
+
+**Decision:** Proceed with plugin - sync plugins are low-risk
+
+### Technical Constraints Discovered
+
+1. **Kobo Firmware Limitations:**
+   - Cannot send custom HTTP headers (except `x-kobo-device`)
+   - Cannot install plugins
+   - Settings in `eReader.conf` are limited
+   - NickelMenu required for OPDS access (jailbreak)
+
+2. **KOReader Capabilities:**
+   - Can install plugins (copy files to `/koreader/plugins/`)
+   - Lua-based plugin architecture
+   - Can send custom HTTP requests
+   - Can access device serial for identification
+   - Native OPDS client support
+
+3. **Security Trade-offs:**
+   - Serial numbers: Somewhat predictable, easy for users
+   - Bearer tokens: Cryptographically secure, requires setup
+   - User accepted security/usability trade-off for self-hosted use
+
+### Why Functionality Trumps Security
+
+**User Quote:** "I want a Kindle system replacement, otherwise I could just use booklore or KOReader. My biggest concern is do any of these limit any of the syncing/downloading implementation I already have. Functionality and features are more important than anything else. Although security does come in at a close second."
+
+**Translation:** 
+- Self-hosted = trusted network environment
+- User understands and accepts risks
+- Willing to document security implications
+- Prioritizes working features over perfect security
+
+**Resulting Architecture:**
+- Kobo: Serial auth (medium security, zero friction)
+- KOReader: Bearer token (high security, requires plugin setup)
+- Both get full feature parity
+- Security implications clearly documented
+
+---
+
+## 11. Updated Implementation Timeline
+
+### Parallel Track Structure
+
+**Track A: Kobo Integration**
+- Phase 1: Enhanced Auth (Week 1)
+- Phase 2a: Kobo Implementation (Week 1-2)
+- Phase 4: Kobo Testing (Week 3)
+
+**Track B: KOReader Plugin**
+- Phase 1: Enhanced Auth (Week 1) [shared]
+- Phase 2b: Plugin Development (Week 2-4)
+- Phase 4: Plugin Testing (Week 4)
+
+**Track C: OPDS Security**
+- Phase 3: OPDS Integration (Week 2-3)
+
+**Track D: Documentation**
+- Phase 5: Final Docs & Release (Week 4)
+
+### Milestones
+
+**Milestone 1 (End of Week 2):** Kobo Fully Functional
+- Serial auth working
+- All sync features operational
+- OPDS access secured
+- Can ship to Kobo users
+
+**Milestone 2 (End of Week 4):** KOReader Plugin Ready
+- Plugin released in separate repo
+- Full feature parity with Kobo
+- Documentation complete
+- Production release
+
+---
+
+## 12. Files & Components Reference
+
+### Critical Files for Implementation
+
+**Authentication Core:**
+- `internal/middleware/device_auth.go:37-108` - Main auth middleware
+- `internal/database/queries/devices.sql` - Device queries
+- `internal/database/models.go` - Device model (has device_identifier)
+
+**Routing:**
+- `internal/router/opds.go:11-12` - OPDS routes (need middleware)
+- `internal/router/sync.go:17-50` - Sync routes
+- `internal/router/device.go` - Device management routes
+
+**Handlers:**
+- `internal/handlers/kobo.go:26-679` - Kobo sync implementation
+- `internal/handlers/koreader.go:23-897` - KOReader sync implementation
+- `internal/handlers/opds.go` - OPDS handler
+
+**Tests:**
+- `cmd/server/tests/kobo_test.go` - Kobo tests
+- `cmd/server/tests/opds_test.go` - OPDS tests
+- `cmd/server/tests/test_helpers.go` - Test utilities
+
+**Documentation (to update):**
+- `docs/user/devices/kobo-setup.md` - Currently has wrong info
+- `docs/user/devices/koreader-setup.md` - Needs Bearer token info
+
+**Sidecar (reference only, not implementing):**
+- `internal/handlers/sidecar.go` - Exists but not wired up
+- Routes not registered in router
+
+---
+
+## 13. Next Steps
+
+### Immediate Actions (When Ready to Proceed)
+
+1. **Review this plan** - Ensure all decisions and context are captured
+2. **Create KOReader plugin repo** - Set up `github.com/bookhoard/koreader-plugin`
+3. **Begin Phase 1** - Enhanced DeviceAuthMiddleware
+4. **Parallel development** - Kobo and KOReader tracks
+
+### Success Criteria (Reiterated)
+
+**Functional:**
+- ✅ Kobo: Enter serial → register → sync works immediately
+- ✅ KOReader: Install plugin → enter token → sync works
+- ✅ Both: Full sync (progress, highlights, notes, bookmarks)
+- ✅ OPDS: Authenticated access on both platforms
+- ✅ Cross-device: Read on one, continue on another
+
+**Security:**
+- ✅ OPDS no longer public
+- ✅ All sync endpoints require auth
+- ✅ Security implications documented
+- ✅ Network security recommendations provided
+
+**User Experience:**
+- ✅ Kobo setup: < 5 minutes
+- ✅ KOReader setup: < 10 minutes  
+- ✅ Clear documentation
+- ✅ Working examples
+
+---
+
+**Plan Status:** Ready for implementation
+**Last Updated:** Based on conversation ending with user decisions
+**Note:** User indicated it's late and not proceeding tonight
+
+**Ready to implement when you are. This plan captures all our discussion and decisions.**
+
+---
+
+## 10. Risk Assessment
+
+**Low Risk:**
+- Serial auth implementation (well-understood pattern)
+- OPDS security (straightforward middleware application)
+- Kobo sync (already implemented, just fixing auth)
+
+**Medium Risk:**
+- KOReader plugin development (Lua learning curve, potential API changes)
+- Cross-device sync conflicts (need clear resolution strategy)
+
+**High Risk:**
+- KOReader API instability (if they change plugin APIs frequently)
+- User adoption (may resist plugin installation)
+
+**Mitigations:**
+- Start with Kobo to prove concept
+- Simple plugin architecture (minimize breaking changes impact)
+- Excellent documentation to reduce friction
+- Community feedback loop
+
+---
+
+## 11. Timeline Summary
+
+| Phase | Duration | Key Deliverable |
+|-------|----------|----------------|
+| Phase 1 | Week 1 | Enhanced auth middleware working |
+| Phase 2 | Week 1-2 | Kobo fully functional |
+| Phase 3 | Week 2-4 | KOReader plugin complete |
+| Phase 4 | Week 2-3 | OPDS secured |
+| Phase 5 | Week 4 | Testing & docs complete |
+
+**Total Duration: 4 weeks**
+
+---
+
+**Next Steps:**
+1. User reviews and approves plan
+2. Answer open questions (Section 9)
+3. Begin Phase 1 implementation
+4. Weekly check-ins on progress
+
+**Ready to proceed?**