Agents tunnels: auto-reconnect with backoff and wake-triggered retry (#310868)

* Agents tunnels: auto-reconnect with backoff and wake-triggered retry

Tunnel-backed remote agent hosts previously had no auto-reconnect
behavior — on laptop sleep / network drop the tunnel would flip to
Disconnected and stay there until the user manually retried.

This adds a reconnect loop inside TunnelAgentHostContribution:

- Detect Connected→Disconnected transitions for still-cached tunnels
  and schedule an immediate reconnect. Only fires when the entry is
  explicitly Disconnected — if the entry has been removed (e.g. user
  clicked "Remove Remote"), we honour the removal and do not reconnect.
- Exponential backoff on consecutive failures: 1s → 30s cap, up to
  10 attempts, then pause.
- Wake-triggered retry: on browser `online` or tab
  `visibilitychange` → visible, resume any paused reconnects.
  Rate-limited to one resume per 10s so rapid tab toggling can't
  hammer a permanently broken endpoint with unbounded attempt bursts.
- Prune all reconnect state when a tunnel is uncached or the
  contribution is disposed.

* Review comment

Co-authored-by: Copilot <copilot@github.com>

* Telemetry

Co-authored-by: Copilot <copilot@github.com>

* Clean up

Co-authored-by: Copilot <copilot@github.com>

---------

Co-authored-by: Copilot <copilot@github.com>

Author: osortega

src/vs/sessions/common/sessionsTelemetry.ts

@@ -111,3 +111,64 @@ type ChangesViewReviewCommentAddedClassification = {
 export function logChangesViewReviewCommentAdded(telemetryService: ITelemetryService, data: { hasExistingFeedback: boolean; hasSuggestion: boolean; isFromPRReview: boolean }): void {
 	telemetryService.publicLog2<ChangesViewReviewCommentAddedEvent, ChangesViewReviewCommentAddedClassification>('vscodeAgents.changesView/reviewCommentAdded', data);
 }
+
+// --- Tunnel agent host connect ---
+
+export type TunnelConnectErrorCategory = 'relayConnectionFailed' | 'auth' | 'network' | 'other';
+export type TunnelConnectFailureReason = 'hostOffline' | 'maxAttemptsReached';
+
+type TunnelConnectAttemptEvent = {
+	isReconnect: boolean;
+	attempt: number;
+	durationMs: number;
+	success: boolean;
+	errorCategory: string;
+};
+
+type TunnelConnectAttemptClassification = {
+	owner: 'osortega';
+	comment: 'Tracks individual agent-host tunnel connect attempts for performance and reliability.';
+	isReconnect: { classification: 'SystemMetaData'; purpose: 'FeatureInsight'; isMeasurement: true; comment: 'Whether this attempt was part of a reconnect cycle (true) or an initial connect (false).' };
+	attempt: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Attempt number within the current connect session (1-based).' };
+	durationMs: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Duration of this individual attempt in milliseconds.' };
+	success: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Whether this individual attempt succeeded.' };
+	errorCategory: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; comment: 'Category of error when the attempt failed (relayConnectionFailed, auth, network, other); empty on success.' };
+};
+
+export function logTunnelConnectAttempt(telemetryService: ITelemetryService, data: { isReconnect: boolean; attempt: number; durationMs: number; success: boolean; errorCategory?: TunnelConnectErrorCategory }): void {
+	telemetryService.publicLog2<TunnelConnectAttemptEvent, TunnelConnectAttemptClassification>('vscodeAgents.tunnelConnect/attempt', {
+		isReconnect: data.isReconnect,
+		attempt: data.attempt,
+		durationMs: data.durationMs,
+		success: data.success,
+		errorCategory: data.errorCategory ?? '',
+	});
+}
+
+type TunnelConnectResolvedEvent = {
+	isReconnect: boolean;
+	totalAttempts: number;
+	totalDurationMs: number;
+	success: boolean;
+	failureReason: string;
+};
+
+type TunnelConnectResolvedClassification = {
+	owner: 'osortega';
+	comment: 'Tracks overall agent-host tunnel connect session outcomes for reliability.';
+	isReconnect: { classification: 'SystemMetaData'; purpose: 'FeatureInsight'; isMeasurement: true; comment: 'Whether the resolved session was a reconnect cycle (true) or an initial connect (false).' };
+	totalAttempts: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Total number of attempts made before resolution.' };
+	totalDurationMs: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Total elapsed time from session start to resolution in milliseconds.' };
+	success: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; isMeasurement: true; comment: 'Whether the connect session ultimately succeeded.' };
+	failureReason: { classification: 'SystemMetaData'; purpose: 'PerformanceAndHealth'; comment: 'Reason the session terminated without connecting (hostOffline, maxAttemptsReached); empty on success.' };
+};
+
+export function logTunnelConnectResolved(telemetryService: ITelemetryService, data: { isReconnect: boolean; totalAttempts: number; totalDurationMs: number; success: boolean; failureReason?: TunnelConnectFailureReason }): void {
+	telemetryService.publicLog2<TunnelConnectResolvedEvent, TunnelConnectResolvedClassification>('vscodeAgents.tunnelConnect/resolved', {
+		isReconnect: data.isReconnect,
+		totalAttempts: data.totalAttempts,
+		totalDurationMs: data.totalDurationMs,
+		success: data.success,
+		failureReason: data.failureReason ?? '',
+	});
+}