Split software arch desc for easier manintenance. Many fixes related to next video playing and remote playback

docs/architecture/07-connectivity.md

@@ -0,0 +1,92 @@
+# Connectivity & Network Architecture
+
+## HTTP Client with Retry Logic
+
+**Location**: `src-tauri/src/jellyfin/http_client.rs`
+
+The HTTP client provides automatic retry with exponential backoff for network resilience:
+
+```rust
+pub struct HttpClient {
+    client: reqwest::Client,
+    config: HttpConfig,
+}
+
+pub struct HttpConfig {
+    pub base_url: String,
+    pub timeout: Duration,        // Default: 10s
+    pub max_retries: u32,         // Default: 3
+}
+```
+
+**Retry Strategy:**
+- Retry delays: 1s, 2s, 4s (exponential backoff)
+- Retries on: Network errors, 5xx server errors
+- No retry on: 4xx client errors, 401/403 authentication errors
+
+**Error Classification:**
+```rust
+pub enum ErrorKind {
+    Network,        // Connection failures, timeouts, DNS errors
+    Authentication, // 401/403 responses
+    Server,         // 5xx server errors
+    Client,         // Other 4xx errors
+}
+```
+
+## Connectivity Monitor
+
+**Location**: `src-tauri/src/connectivity/mod.rs`
+
+The connectivity monitor tracks server reachability with adaptive polling:
+
+```mermaid
+flowchart TB
+    Monitor["ConnectivityMonitor"] --> Poller["Background Task"]
+    Poller --> Check{"Server<br/>Reachable?"}
+    Check -->|"Yes"| Online["30s Interval"]
+    Check -->|"No"| Offline["5s Interval"]
+    Online --> Emit["Emit Events"]
+    Offline --> Emit
+    Emit --> Frontend["Frontend Store"]
+```
+
+**Features:**
+- **Adaptive Polling**: 30s when online, 5s when offline (for quick reconnection detection)
+- **Event Emission**: Emits `connectivity:changed` and `connectivity:reconnected` events
+- **Manual Marking**: Can mark reachable/unreachable based on API call results
+- **Thread-Safe**: Uses Arc<RwLock<>> for shared state
+
+**Tauri Commands:**
+| Command | Description |
+|---------|-------------|
+| `connectivity_check_server` | Manual reachability check |
+| `connectivity_set_server_url` | Update monitored server URL |
+| `connectivity_get_status` | Get current connectivity status |
+| `connectivity_start_monitoring` | Start background monitoring |
+| `connectivity_stop_monitoring` | Stop monitoring |
+| `connectivity_mark_reachable` | Mark server as reachable (after successful API call) |
+| `connectivity_mark_unreachable` | Mark server as unreachable (after failed API call) |
+
+**Frontend Integration:**
+```typescript
+// TypeScript store listens to Rust events
+listen<{ isReachable: boolean }>("connectivity:changed", (event) => {
+  updateConnectivityState(event.payload.isReachable);
+});
+```
+
+## Network Resilience Architecture
+
+The connectivity system provides resilience through multiple layers:
+
+1. **HTTP Client Layer**: Automatic retry with exponential backoff
+2. **Connectivity Monitoring**: Background reachability checks
+3. **Frontend Integration**: Offline mode detection and UI updates
+4. **Sync Queue**: Offline mutations queued for later (see [06-downloads-and-offline.md](06-downloads-and-offline.md))
+
+**Design Principles:**
+- **Fail Fast**: Don't retry 4xx errors (client errors, authentication)
+- **Fail Slow**: Retry network and 5xx errors with increasing delays
+- **Adaptive Polling**: Reduce polling frequency when online, increase when offline
+- **Event-Driven**: Frontend reacts to connectivity changes via events