agentHost: recover failed Copilot turns in place

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

@@ -748,6 +748,9 @@ export interface IAgentChats {
 	 */
 	sendMessage(chat: URI, prompt: string, workingDirectoriesOrDirectory: readonly URI[] | URI | undefined, attachments?: readonly MessageAttachment[], turnId?: string, senderClientId?: string, clientTypeOrContext?: AgentHostClientType | URI | IAgentChatContext, context?: URI | IAgentChatContext): Promise<void>;
 
+	/** Resume a failed turn without adding another user message. */
+	resumeTurn?(chat: URI, turnId: string, context: AgentChatOperationContext, senderClientId?: string, clientType?: AgentHostClientType): Promise<void>;
+
 	/** Abort the in-flight turn for `chat`. */
 	abort(chat: URI, context: AgentChatOperationContext): Promise<void>;
 

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

@@ -23,7 +23,7 @@ export const IAgentHostChatContributions = createDecorator<IAgentHostChatContrib
 export type TurnEndReason =
 	| { readonly kind: 'success' }
 	| { readonly kind: 'cancelled' }
-	| { readonly kind: 'error'; readonly error: ErrorInfo }
+	| { readonly kind: 'error'; readonly error: ErrorInfo; readonly resumable: boolean }
 	| { readonly kind: 'localCommand' };
 
 /** A terminal turn outcome offered to contributions after a turn ended. */

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

@@ -25,3 +25,8 @@ export interface IAgentHostPlanReview {
 export type ChatInputRequestWithPlanReview = ChatInputRequest & {
 	readonly planReview?: IAgentHostPlanReview;
 };
+
+export function isChatInputRequestWithPlanReview(request: ChatInputRequest): request is ChatInputRequestWithPlanReview {
+	const candidate: ChatInputRequestWithPlanReview = request;
+	return candidate.planReview !== undefined;
+}

src/vs/platform/agentHost/common/state/sessionState.ts

@@ -33,6 +33,7 @@ import {
 	type ChatState,
 	type ChatSummary,
 	type ErrorInfo,
+	type ErrorResponsePart,
 	type PendingMessage,
 	type Turn,
 	type AnnotationsState,
@@ -70,8 +71,8 @@ export {
 	type ConfigSchema,
 	type ContentRef, type Customization, type CustomizationDegradedState,
 	type CustomizationErrorState, type CustomizationLoadedState, type CustomizationLoadingState, type CustomizationLoadState, type DirectoryCustomization, type ErrorInfo, type HookCustomization, type FileEdit as ISessionFileDiff, type ToolResultEmbeddedResourceContent as IToolResultBinaryContent, type MarkdownResponsePart, type McpServerCustomization, type MessageAttachment,
-	type MessageResourceAttachment, type MessageEmbeddedResourceAttachment, type MessageAnnotationsAttachment, type MessageChatAttachment, type ModelSelection, type PendingMessage, type PluginCustomization, type ProjectInfo, type PromptCustomization, type ReasoningResponsePart, type ErrorResponsePart,
-	type ResponsePart,
+	type MessageResourceAttachment, type MessageEmbeddedResourceAttachment, type MessageAnnotationsAttachment, type MessageChatAttachment, type ModelSelection, type PendingMessage, type PluginCustomization, type ProjectInfo, type PromptCustomization, type ReasoningResponsePart,
+	type ErrorResponsePart, type ResponsePart,
 	type RootState, type RuleCustomization, type SessionActiveClient,
 	type SessionConfigState, type SessionModelInfo,
 	type SessionState,
@@ -100,6 +101,82 @@ export {
 	type Message
 } from './protocol/state.js';
 
+export function getErrorResponsePart(turn: Turn | ActiveTurn | undefined): ErrorResponsePart | undefined {
+	if (!turn) {
+		return undefined;
+	}
+	const part = turn.responseParts.at(-1);
+	return part?.kind === ResponsePartKind.Error ? part : undefined;
+}
+
+export function createErrorResponsePart(error: ErrorInfo, resumable = false): ErrorResponsePart {
+	return {
+		kind: ResponsePartKind.Error,
+		error,
+		...(resumable ? { resumable: true } : {}),
+	};
+}
+
+export function mergeLogicalTurnUsage(previous: UsageInfo | undefined, current: UsageInfo | undefined): UsageInfo | undefined {
+	if (!previous) {
+		return current;
+	}
+	if (!current) {
+		return previous;
+	}
+
+	const previousMeta = readUsageInfoMeta(previous);
+	const currentMeta = readUsageInfoMeta(current);
+	const cost = sumDefined(previousMeta.cost, currentMeta.cost);
+	const totalNanoAiu = sumDefined(previousMeta.copilotUsage?.totalNanoAiu, currentMeta.copilotUsage?.totalNanoAiu);
+	const turnTokenTotals = mergeTurnTokenTotals(previousMeta.turnTokenTotals, currentMeta.turnTokenTotals);
+	const directTotalNanoAiu = sumDefined(previousMeta.directCopilotUsage?.totalNanoAiu, currentMeta.directCopilotUsage?.totalNanoAiu);
+	const directTurnTokenTotals = mergeTurnTokenTotals(previousMeta.directTurnTokenTotals, currentMeta.directTurnTokenTotals);
+	const meta = previous._meta !== undefined || current._meta !== undefined ? {
+		...previous._meta,
+		...current._meta,
+		...(cost !== undefined ? { cost } : {}),
+		...(previousMeta.copilotUsage || currentMeta.copilotUsage ? {
+			copilotUsage: {
+				...previousMeta.copilotUsage,
+				...currentMeta.copilotUsage,
+				...(totalNanoAiu !== undefined ? { totalNanoAiu } : {}),
+			},
+		} : {}),
+		...(turnTokenTotals ? { turnTokenTotals } : {}),
+		...(directTotalNanoAiu !== undefined ? { directCopilotUsage: { totalNanoAiu: directTotalNanoAiu } } : {}),
+		...(directTurnTokenTotals ? { directTurnTokenTotals } : {}),
+	} : undefined;
+
+	return {
+		...previous,
+		...current,
+		model: current.model ?? previous.model,
+		...(meta ? { _meta: meta } : {}),
+	};
+}
+
+function sumDefined(first: number | undefined, second: number | undefined): number | undefined {
+	return first === undefined ? second : second === undefined ? first : first + second;
+}
+
+function mergeTurnTokenTotals(previous: UsageInfoMeta['turnTokenTotals'], current: UsageInfoMeta['turnTokenTotals']): UsageInfoMeta['turnTokenTotals'] {
+	if (!previous && !current) {
+		return undefined;
+	}
+	const totals = new Map<string, ITurnTokenTotal>();
+	for (const total of [...previous ?? [], ...current ?? []]) {
+		const existing = totals.get(total.model);
+		totals.set(total.model, existing ? {
+			model: total.model,
+			inputTokens: existing.inputTokens + total.inputTokens,
+			cachedTokens: existing.cachedTokens + total.cachedTokens,
+			outputTokens: existing.outputTokens + total.outputTokens,
+		} : { ...total });
+	}
+	return [...totals.values()];
+}
+
 /**
  * Well-known keys that may appear on {@link UsageInfo._meta}.
  * Clients MAY read these to provide enhanced UI (e.g. credit cost display).

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

@@ -35,7 +35,7 @@ import type { InvokeChangesetOperationParams, InvokeChangesetOperationResult } f
 import { AhpErrorCodes, AHP_SESSION_NOT_FOUND, ContentEncoding, JSON_RPC_INTERNAL_ERROR, ProtocolError, ResourceChangeType, ResourceType, ResourceWriteMode, type CreateResourceWatchParams, type CreateResourceWatchResult, type DirectoryEntry, type ResourceCopyParams, type ResourceCopyResult, type ResourceDeleteParams, type ResourceDeleteResult, type ResourceListResult, type ResourceMkdirParams, type ResourceMkdirResult, type ResourceMoveParams, type ResourceMoveResult, type ResourceReadResult, type ResourceResolveParams, type ResourceResolveResult, type ResourceWatchState, type ResourceWriteParams, type ResourceWriteResult, type IStateSnapshot } from '../common/state/sessionProtocol.js';
 import { ChangesSummary, ChatInteractivity, ChatOriginKind, MessageAttachmentKind, type Annotation, type AnnotationEntry, type AnnotationOrigin, type AnnotationsState, type ChatOrigin, type Customization, type Message, type MessageAttachment, type MessageResourceAttachment, type TextRange } from '../common/state/protocol/state.js';
 import type { ChatPendingMessageSetAction, ChatTurnStartedAction, SessionConfigChangedAction } from '../common/state/protocol/actions.js';
-import { ISessionGitHubState, ISessionGitState, MessageKind, ResponsePartKind, SESSION_META_GITHUB_KEY, SESSION_META_GIT_KEY, SESSION_META_MULTI_ROOT_KEY, SESSION_META_SOURCE_CONTROL_KEY, AH_META_CREATED_BY_SESSION_DB_KEY, readSessionCreationReference, readSessionSpawnDepth, withSessionSpawnDepth, withSessionCreationReference, parseSessionCreationReference, SessionLifecycle, SessionStatus, ToolCallStatus, ToolResultContentType, AH_META_WORKSPACELESS_DB_KEY, AH_META_EHCLI_ADOPTED_DB_KEY, AH_META_IS_ARCHIVED_DB_KEY, AH_META_IS_DONE_DB_KEY, AH_META_IS_READ_DB_KEY, buildChatUri, buildDefaultChatUri, buildResourceWatchChannelUri, buildSubagentChatUri, buildSubagentSessionUriPrefix, isAhpChatChannel, isDefaultChatUri, isSubagentChatUri, isSubagentSession, needsSessionGitStateRefresh, parseChatUri, parseDefaultChatUri, parseRequiredSessionUriFromChatUri, parseResourceWatchChannelUri, parseSessionMultiRootMetadata, parseSubagentSessionUri, readSessionExternal, readSessionGitHubState, readSessionGitState, readSessionMultiRootMetadata, readSessionSourceControlState, readSessionWorkspaceless, withSessionExternal, withSessionGitHubState, withSessionGitState, withMessageHiddenFromTranscript, withSessionMultiRootMetadata, withSessionSourceControlState, withSessionStatusFlag, withSessionWorkspaceless, withSessionEhcliAdopted, withSessionFolderPickerDecision, readSessionFolderPickerDecision, parseSessionFolderPickerDecision, SESSION_META_FOLDER_PICKER_KEY, readSessionEhcliAdoptable, type ISessionSourceControlState, type SessionConfigState, type SessionSummary, type ToolResultSubagentContent, type Turn } from '../common/state/sessionState.js';
+import { ISessionGitHubState, ISessionGitState, MessageKind, ResponsePartKind, SESSION_META_GITHUB_KEY, SESSION_META_GIT_KEY, SESSION_META_MULTI_ROOT_KEY, SESSION_META_SOURCE_CONTROL_KEY, AH_META_CREATED_BY_SESSION_DB_KEY, readSessionCreationReference, readSessionSpawnDepth, withSessionSpawnDepth, withSessionCreationReference, parseSessionCreationReference, SessionLifecycle, SessionStatus, ToolCallStatus, ToolResultContentType, TurnState, AH_META_WORKSPACELESS_DB_KEY, AH_META_EHCLI_ADOPTED_DB_KEY, AH_META_IS_ARCHIVED_DB_KEY, AH_META_IS_DONE_DB_KEY, AH_META_IS_READ_DB_KEY, buildChatUri, buildDefaultChatUri, buildResourceWatchChannelUri, buildSubagentChatUri, buildSubagentSessionUriPrefix, getErrorResponsePart, isAhpChatChannel, isChatReadOnly, isDefaultChatUri, isSubagentChatUri, isSubagentSession, needsSessionGitStateRefresh, parseChatUri, parseDefaultChatUri, parseRequiredSessionUriFromChatUri, parseResourceWatchChannelUri, parseSessionMultiRootMetadata, parseSubagentSessionUri, readSessionExternal, readSessionGitHubState, readSessionGitState, readSessionMultiRootMetadata, readSessionSourceControlState, readSessionWorkspaceless, withMessageHiddenFromTranscript, withSessionExternal, withSessionGitHubState, withSessionGitState, withSessionMultiRootMetadata, withSessionSourceControlState, withSessionStatusFlag, withSessionWorkspaceless, withSessionEhcliAdopted, withSessionFolderPickerDecision, readSessionFolderPickerDecision, parseSessionFolderPickerDecision, SESSION_META_FOLDER_PICKER_KEY, readSessionEhcliAdoptable, type ISessionSourceControlState, type SessionConfigState, type SessionSummary, type ToolResultSubagentContent, type Turn } from '../common/state/sessionState.js';
 import { readToolCallMeta } from '../common/meta/agentToolCallMeta.js';
 import { isHostSnapshotAttachment, toHostSnapshotAttachmentMeta } from '../common/meta/agentSnapshotAttachmentMeta.js';
 import { readEphemeralSessionMeta, withEphemeralSessionMeta } from '../common/meta/agentEphemeralSessionMeta.js';
@@ -4391,6 +4391,42 @@ export class AgentService extends Disposable implements IAgentService {
 
 	private _dispatchActionNow(channel: string, sessionChannel: string, action: SessionAction | ChatAction | TerminalAction | ClientChangesetAction | ClientAnnotationsAction | IRootConfigChangedAction, clientId: string, clientSeq: number, clientContext: IAgentHostClientTelemetryContext): void {
 		const origin = { clientId, clientSeq };
+		if (action.type === ActionType.ChatTurnCancelled) {
+			const resumedDuration = this._sideEffects.getResumedTurnDuration(channel, action.turnId);
+			if (resumedDuration !== undefined) {
+				action = { ...action, duration: resumedDuration };
+			}
+		}
+		let resumedTurn: Turn | undefined;
+		if (action.type === ActionType.ChatTurnResume) {
+			if (!isAhpChatChannel(channel)) {
+				this._stateManager.rejectClientAction(channel, action, origin, 'Turn resume requires a chat channel.');
+				return;
+			}
+			const chatState = this._stateManager.getChatState(channel);
+			const sessionState = this._stateManager.getSessionState(sessionChannel);
+			const sessionArchived = ((sessionState?.status ?? 0) & SessionStatus.IsArchived) === SessionStatus.IsArchived;
+			const turn = chatState?.turns.at(-1);
+			const errorPart = getErrorResponsePart(turn);
+			const provider = this._findProviderForSession(sessionChannel);
+			if (chatState?.activeTurn) {
+				this._stateManager.rejectClientAction(channel, action, origin, 'Cannot resume while a turn is active.');
+				return;
+			}
+			if (isChatReadOnly(chatState?.interactivity, sessionArchived)) {
+				this._stateManager.rejectClientAction(channel, action, origin, 'Cannot resume a read-only or archived chat.');
+				return;
+			}
+			if (!turn || turn.id !== action.turnId || turn.state !== TurnState.Error || errorPart?.resumable !== true) {
+				this._stateManager.rejectClientAction(channel, action, origin, 'The requested turn is not the latest resumable errored turn.');
+				return;
+			}
+			if (!provider?.chats.resumeTurn) {
+				this._stateManager.rejectClientAction(channel, action, origin, 'The session provider does not support turn resume.');
+				return;
+			}
+			resumedTurn = turn;
+		}
 		if (action.type === ActionType.ChatTurnStarted && this._isTurnIdUsedByAnotherChat(sessionChannel, channel, action.turnId)) {
 			this._stateManager.rejectClientAction(channel, action, origin, 'Turn id is already used by another chat in this session.');
 			return;
@@ -4441,7 +4477,7 @@ export class AgentService extends Disposable implements IAgentService {
 				this._editAttributionService.setEnabled(editTelemetryEnabled);
 			}
 		}
-		this._sideEffects.handleAction(channel, action, clientId, clientContext);
+		this._sideEffects.handleAction(channel, action, clientId, clientContext, resumedTurn);
 	}
 	private _getUnresolvedPeerChats(sessionChannel: string): readonly string[] | undefined {
 		return this._stateManager.getSessionState(sessionChannel)?.chats.filter(chat => !isDefaultChatUri(chat.resource) && !this._stateManager.getChatState(chat.resource)).map(chat => chat.resource);