Perf: Dedupe tool-definition JSON across telemetry/OTel sites

extensions/copilot/src/extension/byok/vscode-node/anthropicProvider.ts

@@ -16,7 +16,7 @@ import { ContextManagementResponse, CUSTOM_TOOL_SEARCH_NAME, getContextManagemen
 import { IToolDeferralService } from '../../../platform/networking/common/toolDeferralService';
 import { IResponseDelta, OpenAiFunctionTool } from '../../../platform/networking/common/fetch';
 import { APIUsage } from '../../../platform/networking/common/openai';
-import { CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, type OTelModelOptions, StdAttr, toSystemInstructions, toToolDefinitions, truncateForOTel } from '../../../platform/otel/common/index';
+import { CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, type OTelModelOptions, StdAttr, stringifyToolDefinitionsForOTel, toSystemInstructions, truncateForOTel } from '../../../platform/otel/common/index';
 import { IOTelService, SpanKind, SpanStatusCode } from '../../../platform/otel/common/otelService';
 import { IRequestLogger } from '../../../platform/requestLogger/common/requestLogger';
 import { retrieveCapturingTokenByCorrelation, runWithCapturingToken } from '../../../platform/requestLogger/node/requestLogger';
@@ -502,9 +502,9 @@ export class AnthropicLMProvider extends AbstractLanguageModelChatProvider {
 			if (this._otelService.config.captureContent) {
 				// Tool definitions on the chat span (issue #299934) with `parameters`
 				// per OTel GenAI semantic conventions (issue #300318).
-				const toolDefs = toToolDefinitions(options.tools);
-				if (toolDefs) {
-					otelSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(JSON.stringify(toolDefs), this._otelService.config.maxAttributeSizeChars));
+				const toolDefsJson = stringifyToolDefinitionsForOTel(options.tools);
+				if (toolDefsJson) {
+					otelSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(toolDefsJson, this._otelService.config.maxAttributeSizeChars));
 				}
 				try {
 					const { systemTexts, inputMsgs } = buildOTelInputFromChatMessages(messages);

extensions/copilot/src/extension/byok/vscode-node/geminiNativeProvider.ts

@@ -10,7 +10,7 @@ import { ILogService } from '../../../platform/log/common/logService';
 import { IResponseDelta, OpenAiFunctionTool } from '../../../platform/networking/common/fetch';
 import { APIUsage } from '../../../platform/networking/common/openai';
 import { CustomDataPartMimeTypes } from '../../../platform/endpoint/common/endpointTypes';
-import { CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, type OTelModelOptions, StdAttr, toSystemInstructions, toToolDefinitions, truncateForOTel } from '../../../platform/otel/common/index';
+import { CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, type OTelModelOptions, StdAttr, stringifyToolDefinitionsForOTel, toSystemInstructions, truncateForOTel } from '../../../platform/otel/common/index';
 import { IOTelService, SpanKind, SpanStatusCode } from '../../../platform/otel/common/otelService';
 import { IRequestLogger } from '../../../platform/requestLogger/common/requestLogger';
 import { retrieveCapturingTokenByCorrelation, runWithCapturingToken } from '../../../platform/requestLogger/node/requestLogger';
@@ -363,9 +363,9 @@ export class GeminiNativeBYOKLMProvider extends AbstractLanguageModelChatProvide
 			if (this._otelService.config.captureContent) {
 				// Tool definitions on the chat span (issue #299934) with `parameters`
 				// per OTel GenAI semantic conventions (issue #300318).
-				const toolDefs = toToolDefinitions(options.tools);
-				if (toolDefs) {
-					otelSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(JSON.stringify(toolDefs), this._otelService.config.maxAttributeSizeChars));
+				const toolDefsJson = stringifyToolDefinitionsForOTel(options.tools);
+				if (toolDefsJson) {
+					otelSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(toolDefsJson, this._otelService.config.maxAttributeSizeChars));
 				}
 				try {
 					const { systemTexts, inputMsgs } = buildOTelInputFromChatMessages(messages);

extensions/copilot/src/extension/intents/node/toolCallingLoop.ts

@@ -22,7 +22,7 @@ import { ILogService } from '../../../platform/log/common/logService';
 import { isOpenAIContextManagementResponse, OpenAiFunctionDef } from '../../../platform/networking/common/fetch';
 import { IMakeChatRequestOptions } from '../../../platform/networking/common/networking';
 import { OpenAIContextManagementResponse } from '../../../platform/networking/common/openai';
-import { CopilotChatAttr, emitAgentTurnEvent, emitSessionStartEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, GitHubCopilotAttr, resolveWorkspaceOTelMetadata, StdAttr, truncateForOTel, workspaceMetadataToOTelAttributes } from '../../../platform/otel/common/index';
+import { CopilotChatAttr, emitAgentTurnEvent, emitSessionStartEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, GitHubCopilotAttr, resolveWorkspaceOTelMetadata, StdAttr, stringifyToolDefinitionsForOTel, truncateForOTel, workspaceMetadataToOTelAttributes } from '../../../platform/otel/common/index';
 import { IOTelService, ISpanHandle, SpanKind, SpanStatusCode } from '../../../platform/otel/common/otelService';
 import { IRequestLogger } from '../../../platform/requestLogger/common/requestLogger';
 import { getCurrentCapturingToken } from '../../../platform/requestLogger/node/requestLogger';
@@ -893,14 +893,10 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 						// Includes `parameters` (inputSchema) per OTel GenAI semantic convention so
 						// trace viewers can render full tool signatures (issue #300318).
 						if (result.availableTools.length > 0) {
-							span.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(JSON.stringify(
-								result.availableTools.map(t => ({
-									type: 'function',
-									name: t.name,
-									description: t.description,
-									parameters: t.inputSchema,
-								}))
-							)));
+							const toolDefsJson = stringifyToolDefinitionsForOTel(result.availableTools);
+							if (toolDefsJson) {
+								span.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(toolDefsJson));
+							}
 						}
 					}
 					span.setStatus(SpanStatusCode.OK);
@@ -1207,15 +1203,13 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 		// starts in fetch(). This lets the debug logger write tools_*.json early.
 		if (!this.toolsAvailableEmitted && this.agentSpan && availableTools.length > 0) {
 			this.toolsAvailableEmitted = true;
-			this.agentSpan.addEvent('tools_available', {
-				toolDefinitions: truncateForOTel(JSON.stringify(availableTools.map(t => ({
-					type: 'function',
-					name: t.name,
-					description: t.description,
-					parameters: t.inputSchema,
-				})))),
-				...(this.chatSessionIdForTools ? { [CopilotChatAttr.CHAT_SESSION_ID]: this.chatSessionIdForTools } : {}),
-			});
+			const toolDefsJson = stringifyToolDefinitionsForOTel(availableTools);
+			if (toolDefsJson) {
+				this.agentSpan.addEvent('tools_available', {
+					toolDefinitions: truncateForOTel(toolDefsJson),
+					...(this.chatSessionIdForTools ? { [CopilotChatAttr.CHAT_SESSION_ID]: this.chatSessionIdForTools } : {}),
+				});
+			}
 		}
 
 		const context = this.createPromptContext(availableTools, outputStream);

extensions/copilot/src/extension/prompt/node/chatMLFetcher.ts

@@ -28,7 +28,7 @@ import { sendEngineMessagesTelemetry } from '../../../platform/networking/node/c
 import { CAPIWebSocketErrorEvent, IChatWebSocketManager, isCAPIWebSocketError } from '../../../platform/networking/node/chatWebSocketManager';
 import { sendCommunicationErrorTelemetry } from '../../../platform/networking/node/stream';
 import { ChatFailKind, ChatRequestCanceled, ChatRequestFailed, ChatResults, FetchResponseKind } from '../../../platform/openai/node/fetch';
-import { collectSystemTextsFromRequestBody, CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, normalizeProviderMessages, StdAttr, toSystemInstructions, toToolDefinitions, truncateForOTel } from '../../../platform/otel/common/index';
+import { collectSystemTextsFromRequestBody, CopilotChatAttr, emitInferenceDetailsEvent, GenAiAttr, GenAiMetrics, GenAiOperationName, GenAiProviderName, normalizeProviderMessages, StdAttr, stringifyToolDefinitionsForOTel, stringifyToolsRawForTelemetry, toSystemInstructions, truncateForOTel } from '../../../platform/otel/common/index';
 import { IOTelService, ISpanHandle, SpanKind, SpanStatusCode } from '../../../platform/otel/common/otelService';
 import { IRequestLogger } from '../../../platform/requestLogger/common/requestLogger';
 import { getCurrentCapturingToken } from '../../../platform/requestLogger/node/requestLogger';
@@ -295,9 +295,9 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 					// Tool definitions: emit on every chat span so trace viewers can render the
 					// tool catalog per LLM call (issue #299934). Includes `parameters` per
 					// OTel GenAI semantic conventions (issue #300318).
-					const toolDefs = toToolDefinitions(requestBody.tools);
-					if (toolDefs) {
-						otelInferenceSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(JSON.stringify(toolDefs), this._otelService.config.maxAttributeSizeChars));
+					const toolDefsJson = stringifyToolDefinitionsForOTel(requestBody.tools);
+					if (toolDefsJson) {
+						otelInferenceSpan.setAttribute(GenAiAttr.TOOL_DEFINITIONS, truncateForOTel(toolDefsJson, this._otelService.config.maxAttributeSizeChars));
 					}
 					// Cache-relevant request options. Anything in this blob, when changed
 					// between two requests, will invalidate the prompt cache even when
@@ -1171,6 +1171,10 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 			if (key === 'messages' || key === 'input') {
 				continue;
 			} // Skip messages (PII)
+			if (key === 'tools') {
+				telemetryData.properties[`request.option.${key}`] = stringifyToolsRawForTelemetry(value as ReadonlyArray<unknown> | undefined) ?? 'undefined';
+				continue;
+			}
 			telemetryData.properties[`request.option.${key}`] = JSON.stringify(value) ?? 'undefined';
 		}
 		this._telemetryService.sendGHTelemetryEvent('request.sent', telemetryData.properties, telemetryData.measurements);
@@ -1179,7 +1183,7 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 			this._telemetryService.sendEnhancedGHTelemetryEvent('request.options.tools', multiplexProperties({
 				headerRequestId: ourRequestId,
 				conversationId,
-				messagesJson: JSON.stringify(request.tools),
+				messagesJson: stringifyToolsRawForTelemetry(request.tools)!,
 			}), telemetryData.measurements);
 		}
 
@@ -1445,6 +1449,10 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 			if (key === 'messages' || key === 'input') {
 				continue;
 			} // Skip messages (PII)
+			if (key === 'tools') {
+				telemetryData.properties[`request.option.${key}`] = stringifyToolsRawForTelemetry(value as ReadonlyArray<unknown> | undefined) ?? 'undefined';
+				continue;
+			}
 			telemetryData.properties[`request.option.${key}`] = JSON.stringify(value) ?? 'undefined';
 		}
 
@@ -1459,7 +1467,7 @@ export class ChatMLFetcherImpl extends AbstractChatMLFetcher {
 			this._telemetryService.sendEnhancedGHTelemetryEvent('request.options.tools', multiplexProperties({
 				headerRequestId: ourRequestId,
 				conversationId: telemetryProperties?.conversationId,
-				messagesJson: JSON.stringify(request.tools),
+				messagesJson: stringifyToolsRawForTelemetry(request.tools)!,
 			}), telemetryData.measurements);
 		}
 

extensions/copilot/src/platform/otel/common/genAiEvents.ts

@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { GenAiAttr, GenAiOperationName, StdAttr } from './genAiAttributes';
-import { normalizeProviderMessages, toSystemInstructions, truncateForOTel } from './messageFormatters';
+import { normalizeProviderMessages, stringifyToolsRawForTelemetry, toSystemInstructions, truncateForOTel } from './messageFormatters';
 import type { IOTelService } from './otelService';
 import { type WorkspaceOTelMetadata, workspaceMetadataToOTelAttributes } from './workspaceOTelMetadata';
 
@@ -71,7 +71,10 @@ export function emitInferenceDetailsEvent(
 			}
 		}
 		if (request.tools !== undefined) {
-			attributes[GenAiAttr.TOOL_DEFINITIONS] = truncateForOTel(JSON.stringify(request.tools), maxLen);
+			const toolsJson = stringifyToolsRawForTelemetry(request.tools as ReadonlyArray<unknown> | undefined);
+			if (toolsJson !== undefined) {
+				attributes[GenAiAttr.TOOL_DEFINITIONS] = truncateForOTel(toolsJson, maxLen);
+			}
 		}
 	}
 

extensions/copilot/src/platform/otel/common/index.ts

@@ -7,7 +7,7 @@ export { CopilotChatAttr, CopilotCliSdkAttr, FILE_TOOL_NAMES, GenAiAttr, GenAiOp
 export type { AgentType, EditOperationType, HookDecision } from './genAiAttributes';
 export { emitAgentTurnEvent, emitCloudSessionInvokeEvent, emitEditFeedbackEvent, emitEditHunkActionEvent, emitEditSurvivalEvent, emitInferenceDetailsEvent, emitInlineDoneEvent, emitSessionStartEvent, emitToolCallEvent, emitUserFeedbackEvent } from './genAiEvents';
 export { GenAiMetrics } from './genAiMetrics';
-export { collectSystemTextsFromRequestBody, extractTextFromContent, normalizeProviderMessages, toInputMessages, toOutputMessages, toSystemInstructions, toToolDefinitions, truncateForOTel } from './messageFormatters';
+export { collectSystemTextsFromRequestBody, extractTextFromContent, normalizeProviderMessages, stringifyToolDefinitionsForOTel, stringifyToolsRawForTelemetry, toInputMessages, toOutputMessages, toSystemInstructions, toToolDefinitions, truncateForOTel } from './messageFormatters';
 export { NoopOTelService } from './noopOtelService';
 export { resolveOTelConfig, DEFAULT_OTLP_ENDPOINT, type OTelConfig, type OTelConfigInput } from './otelConfig';
 export { IOTelService, SpanKind, SpanStatusCode, type ICompletedSpanData, type ISpanEventData, type ISpanEventRecord, type ISpanHandle, type OTelModelOptions, type SpanOptions, type TraceContext } from './otelService';

extensions/copilot/src/platform/otel/common/messageFormatters.ts

@@ -459,3 +459,73 @@ export function toToolDefinitions(tools: ReadonlyArray<{
 	}
 	return out.length > 0 ? out : undefined;
 }
+
+// Tool-definition JSON is multi-MB and reused across many telemetry/OTel sites
+// per LLM round, often byte-identical across consecutive agent-loop rounds.
+// Intern by array reference (WeakMap) plus a single-slot last-string cache so
+// content-equal serializations from distinct refs collapse to one instance.
+
+const toolDefsJsonByRef = new WeakMap<object, string>();
+const toolsRawJsonByRef = new WeakMap<object, string>();
+let lastToolDefsJson: string | undefined;
+let lastToolsRawJson: string | undefined;
+
+function internToolDefsString(s: string): string {
+	if (lastToolDefsJson !== undefined && lastToolDefsJson === s) {
+		return lastToolDefsJson;
+	}
+	lastToolDefsJson = s;
+	return s;
+}
+
+function internToolsRawString(s: string): string {
+	if (lastToolsRawJson !== undefined && lastToolsRawJson === s) {
+		return lastToolsRawJson;
+	}
+	lastToolsRawJson = s;
+	return s;
+}
+
+/**
+ * Return the OTel-normalized JSON string for a tools array, memoized so all
+ * telemetry/span sites within (and across consecutive identical rounds of) an
+ * LLM call share a single string instance. Returns `undefined` if no
+ * normalized tools would be emitted.
+ */
+export function stringifyToolDefinitionsForOTel(tools: Parameters<typeof toToolDefinitions>[0]): string | undefined {
+	if (!tools || tools.length === 0) {
+		return undefined;
+	}
+	const cached = toolDefsJsonByRef.get(tools);
+	if (cached !== undefined) {
+		return cached;
+	}
+	const defs = toToolDefinitions(tools);
+	if (!defs) {
+		return undefined;
+	}
+	const s = internToolDefsString(JSON.stringify(defs));
+	toolDefsJsonByRef.set(tools, s);
+	return s;
+}
+
+/**
+ * Return `JSON.stringify(tools)` memoized by array reference, with a
+ * single-slot content intern so consecutive rounds producing identical content
+ * share one string instance. Used for telemetry sinks that consume the raw
+ * tools shape rather than the OTel-normalized one. Mirrors `JSON.stringify`
+ * exactly: returns `'[]'` for an empty array and `undefined` only when
+ * `tools` itself is `undefined`.
+ */
+export function stringifyToolsRawForTelemetry(tools: ReadonlyArray<unknown> | undefined): string | undefined {
+	if (!tools) {
+		return undefined;
+	}
+	const cached = toolsRawJsonByRef.get(tools);
+	if (cached !== undefined) {
+		return cached;
+	}
+	const s = internToolsRawString(JSON.stringify(tools));
+	toolsRawJsonByRef.set(tools, s);
+	return s;
+}