agentHost: retain recently used sessions

src/vs/platform/agentHost/common/agentHostSubscriptionService.ts

@@ -0,0 +1,39 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { URI } from '../../../base/common/uri.js';
+import { createDecorator } from '../../instantiation/common/instantiation.js';
+import { parseAnnotationsUri } from './annotationsUri.js';
+import { parseChangesetUri } from './changesetUri.js';
+import { parseDefaultChatUri, parseSubagentSessionUri } from './state/sessionState.js';
+
+export const IAgentHostSubscriptionService = createDecorator<IAgentHostSubscriptionService>('agentHostSubscriptionService');
+
+/**
+ * Authoritative registry of logical protocol clients observing Agent Host state.
+ */
+export interface IAgentHostSubscriptionService {
+	readonly _serviceBrand: undefined;
+
+	readonly subscribedResources: Iterable<URI>;
+
+	addSubscriber(resource: URI, clientId: string): boolean;
+	removeSubscriber(resource: URI, clientId: string): boolean;
+	hasSubscribers(resource: URI): boolean;
+	hasSessionSubscribers(resource: URI): boolean;
+}
+
+export function resolveAgentHostSession(resource: URI): URI {
+	const resourceString = resource.toString();
+	const changesetSession = parseChangesetUri(resourceString)?.sessionUri;
+	const annotationsSession = parseAnnotationsUri(resourceString)?.sessionUri;
+	const chatSession = parseDefaultChatUri(resourceString);
+	let session = URI.parse(changesetSession ?? annotationsSession ?? chatSession ?? resourceString);
+	let subagent;
+	while ((subagent = parseSubagentSessionUri(session))) {
+		session = subagent.parentSession;
+	}
+	return session;
+}

src/vs/platform/agentHost/common/agentService.ts

@@ -218,13 +218,11 @@ export const AgentHostClaudeAgentEnabledEnvVar = 'VSCODE_AGENT_HOST_CLAUDE_AGENT
  */
 export const AgentHostCodexAgentEnabledEnvVar = 'VSCODE_AGENT_HOST_CODEX_AGENT_ENABLED';
 
-/**
- * Overrides the grace period (in milliseconds) before an idle, fully
- * unsubscribed session is released from memory. Defaults to 30_000. Primarily a
- * test hook so real-SDK integration tests can force a prompt release without
- * waiting the full production grace; production does not set it.
- */
-export const AgentHostSessionReleaseGraceMsEnvVar = 'VSCODE_AGENT_HOST_SESSION_RELEASE_GRACE_MS';
+/** Overrides the soft cap on resident session roots. Primarily used by integration tests. */
+export const AgentHostSessionResidencyLimitEnvVar = 'VSCODE_AGENT_HOST_SESSION_RESIDENCY_LIMIT';
+
+/** Overrides the retry delay after a provider temporarily vetoes session release. Primarily used by integration tests. */
+export const AgentHostSessionReleaseRetryMsEnvVar = 'VSCODE_AGENT_HOST_SESSION_RELEASE_RETRY_MS';
 
 /**
  * Resolves the effective enable state for a Claude/Codex provider from the

src/vs/platform/agentHost/node/agentHostServices.ts

@@ -24,6 +24,7 @@ import { IAgentHostChatContributions } from '../common/agentHostChatContribution
 import { IAgentHostCheckpointService } from '../common/agentHostCheckpointService.js';
 import { IAgentHostGitStateService } from '../common/agentHostGitStateService.js';
 import { IAgentHostReviewService } from '../common/agentHostReviewService.js';
+import { IAgentHostSubscriptionService } from '../common/agentHostSubscriptionService.js';
 import { CopilotApiService, ICopilotApiService } from './shared/copilotApiService.js';
 import { AgentHostFileMonitorService, IAgentHostFileMonitorService } from './agentHostFileMonitorService.js';
 import { AgentHostGitService } from './agentHostGitService.js';
@@ -48,6 +49,7 @@ import { AgentHostGitStateService } from './agentHostGitStateService.js';
 import { AgentHostManagedSettingsService, IAgentHostManagedSettingsService } from './agentHostManagedSettingsService.js';
 import { AgentHostPromptCache, IAgentHostPromptCache } from './agentHostPromptCache.js';
 import { AgentHostReviewService } from './agentHostReviewService.js';
+import { AgentHostSubscriptionService } from './agentHostSubscriptionService.js';
 import { AgentHostSessionTitleSignal, IAgentHostSessionTitleSignal } from './agentHostSessionTitleSignal.js';
 import { AgentHostStorageService, IAgentHostStorageService } from './agentHostStorageService.js';
 import { AgentHostTerminalManager, IAgentHostTerminalManager } from './agentHostTerminalManager.js';
@@ -96,6 +98,7 @@ export function registerAgentHostCoreServices(services: ServiceCollection, input
 	registerService(services, IAgentHostPromptCache, new SyncDescriptor(AgentHostPromptCache));
 	registerService(services, IAgentHostSessionTitleSignal, new SyncDescriptor(AgentHostSessionTitleSignal));
 	registerService(services, IAgentHostChangesetSubscriptionService, new SyncDescriptor(AgentHostChangesetSubscriptionService));
+	registerService(services, IAgentHostSubscriptionService, new SyncDescriptor(AgentHostSubscriptionService));
 	registerService(services, IAgentHostChangesetOperationService, new SyncDescriptor(AgentHostChangesetOperationService));
 	registerService(services, IAgentHostReviewService, new SyncDescriptor(AgentHostReviewService));
 	registerService(services, IAgentHostChangesetService, new SyncDescriptor(AgentHostChangesetService));

src/vs/platform/agentHost/node/agentHostStateManager.ts

@@ -1239,8 +1239,8 @@ export class AgentHostStateManager extends Disposable {
 	 * be emitted as a side-effect of this call.
 	 *
 	 * Per-session changesets are intentionally NOT torn down here: this method
-	 * is also used as an idle-eviction (LRU) hook (see
-	 * `AgentService._maybeEvictIdleSession`) and the session list view keeps a
+	 * is also used by `AgentSessionResidency` for residency eviction, and
+	 * the session list view keeps a
 	 * changeset subscription open per visible row to render the diff chip.
 	 * Tearing down on eviction would clear the chip on the list while the row
 	 * is still on screen. Permanent-delete paths (`deleteSession`,

src/vs/platform/agentHost/node/agentHostSubscriptionService.ts

@@ -0,0 +1,56 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { ResourceMap } from '../../../base/common/map.js';
+import { URI } from '../../../base/common/uri.js';
+import { IAgentHostSubscriptionService, resolveAgentHostSession } from '../common/agentHostSubscriptionService.js';
+
+export class AgentHostSubscriptionService implements IAgentHostSubscriptionService {
+	declare readonly _serviceBrand: undefined;
+
+	private readonly _subscribers = new ResourceMap<Set<string>>();
+
+	get subscribedResources(): Iterable<URI> {
+		return this._subscribers.keys();
+	}
+
+	addSubscriber(resource: URI, clientId: string): boolean {
+		let subscribers = this._subscribers.get(resource);
+		const firstForResource = !subscribers || subscribers.size === 0;
+		if (!subscribers) {
+			subscribers = new Set();
+			this._subscribers.set(resource, subscribers);
+		}
+		subscribers.add(clientId);
+		return firstForResource;
+	}
+
+	removeSubscriber(resource: URI, clientId: string): boolean {
+		const subscribers = this._subscribers.get(resource);
+		if (!subscribers) {
+			return false;
+		}
+		subscribers.delete(clientId);
+		if (subscribers.size > 0) {
+			return false;
+		}
+		this._subscribers.delete(resource);
+		return true;
+	}
+
+	hasSubscribers(resource: URI): boolean {
+		return this._subscribers.has(resource);
+	}
+
+	hasSessionSubscribers(resource: URI): boolean {
+		const sessionKey = resolveAgentHostSession(resource).toString();
+		for (const subscribedResource of this._subscribers.keys()) {
+			if (resolveAgentHostSession(subscribedResource).toString() === sessionKey) {
+				return true;
+			}
+		}
+		return false;
+	}
+}