Add auto-reconnect with exponential backoff

Sessions configured with auto-reconnect will automatically attempt to
re-establish the connection when unexpectedly disconnected. Uses
exponential backoff (1s, 2s, 4s, 8s... up to 30s) with a configurable
maximum number of attempts (default 5).

- New SessionReconnecting state with pulsing indicator in tab bar
- SSH and Telnet profiles gain autoReconnect and maxReconnectTries fields
- RAW protocol already had autoReconnect; now uses the shared mechanism
- CancelReconnect API to abort in-progress reconnection
- Frontend shows reconnect attempt notifications
- Profile editor exposes toggle and max attempts in Advanced/Reconnection

frontend/src/css/tabs.css

@@ -125,9 +125,17 @@
 
 .tab-status.is-connected    { background: var(--success); }
 .tab-status.is-connecting   { background: var(--warning); animation: pulse-dot 1.2s ease infinite; }
+.tab-status.is-reconnecting { background: var(--warning); animation: pulse-dot 0.8s ease infinite; }
 .tab-status.is-error        { background: var(--error); }
 .tab-status.is-disconnected { background: var(--text-tertiary); }
 
+/* Also match the status-* pattern used by updateSessionState */
+.tab-status.status-connected    { background: var(--success); }
+.tab-status.status-connecting   { background: var(--warning); animation: pulse-dot 1.2s ease infinite; }
+.tab-status.status-reconnecting { background: var(--warning); animation: pulse-dot 0.8s ease infinite; }
+.tab-status.status-error        { background: var(--error); }
+.tab-status.status-disconnected { background: var(--text-tertiary); }
+
 /* -----------------------------------------------------------------------
    SFTP toggle button — revealed on hover (SSH tabs only)
    ----------------------------------------------------------------------- */

frontend/src/js/app.js

@@ -134,10 +134,21 @@ class App {
             this.terminals.handleData(payload.sessionID, payload.data);
         });
 
-        // Session state transitions (connecting → connected → disconnected)
+        // Session state transitions (connecting → connected → reconnecting → disconnected)
         window.runtime.EventsOn('session:state', (payload) => {
             this.tabs.updateSessionState(payload.sessionID, payload.state, payload.error);
             this.updateStatusBar();
+
+            // Show reconnecting notification
+            if (payload.state === 'reconnecting') {
+                const attempt = payload.attempt || 1;
+                const maxRetries = payload.maxRetries || 5;
+                const delaySec = payload.delaySec || 1;
+                this.notifications.info(
+                    `Reconnecting (attempt ${attempt}/${maxRetries}) in ${delaySec}s…`
+                );
+            }
+
             // Once connected, ensure the backend PTY has the correct dimensions.
             // The initial fit happens before the SSH handshake completes, so the
             // onResize callback fires when the backend isn't ready. By the time

frontend/src/js/profiles.js

@@ -406,6 +406,10 @@ class ProfileEditor {
             this._field('number', 'ssh.keepaliveInterval', 'Keepalive Interval (s)', ssh.keepaliveInterval, { min: 0 }),
             this._field('number', 'ssh.keepaliveCountMax', 'Max Missed Keepalives', ssh.keepaliveCountMax, { min: 0 }),
             this._field('toggle', 'ssh.compression', 'Compression', ssh.compression),
+            this._field('toggle', 'ssh.autoReconnect', 'Auto-Reconnect', ssh.autoReconnect, {
+                help: 'Automatically reconnect with exponential backoff when the connection drops',
+            }),
+            this._field('number', 'ssh.maxReconnectTries', 'Max Reconnect Attempts', ssh.maxReconnectTries || 5, { min: 1, max: 20 }),
         ], true));
 
         return sections;
@@ -447,6 +451,13 @@ class ProfileEditor {
             this._field('toggle', 'telnet.negotiationDebug', 'Debug Negotiation', tel.negotiationDebug),
         ], true));
 
+        sections.push(this._renderSection('Reconnection', [
+            this._field('toggle', 'telnet.autoReconnect', 'Auto-Reconnect', tel.autoReconnect, {
+                help: 'Automatically reconnect with exponential backoff when the connection drops',
+            }),
+            this._field('number', 'telnet.maxReconnectTries', 'Max Reconnect Attempts', tel.maxReconnectTries || 5, { min: 1, max: 20 }),
+        ], true));
+
         return sections;
     }
 
@@ -908,6 +919,8 @@ class ProfileEditor {
             p.ssh.compression = val('ssh.compression') || false;
             p.ssh.agentAuth = val('ssh.agentAuth') || false;
             p.ssh.agentForwarding = val('ssh.agentForwarding') || false;
+            p.ssh.autoReconnect = val('ssh.autoReconnect') || false;
+            p.ssh.maxReconnectTries = val('ssh.maxReconnectTries') ?? 5;
             p.ssh.startupCommand = val('ssh.startupCommand') || '';
 
             const authStr = val('ssh.authMethods');
@@ -970,6 +983,8 @@ class ProfileEditor {
             p.telnet.encoding = val('telnet.encoding') || 'utf-8';
             p.telnet.lineEnding = val('telnet.lineEnding') || 'crlf';
             p.telnet.negotiationDebug = val('telnet.negotiationDebug') || false;
+            p.telnet.autoReconnect = val('telnet.autoReconnect') || false;
+            p.telnet.maxReconnectTries = val('telnet.maxReconnectTries') ?? 5;
         }
 
         // RAW-specific

frontend/src/js/utils.js

@@ -251,6 +251,7 @@ function stateLabel(state) {
         case 'connecting': return 'Connecting';
         case 'connected': return 'Connected';
         case 'disconnected': return 'Disconnected';
+        case 'reconnecting': return 'Reconnecting';
         case 'error': return 'Error';
         default: return state || 'Unknown';
     }