fix: prefer unified sessions for subagent attribution

Preserve Copilot subagent metadata and per-agent accounting snapshots in unified sessions. Read structured attribution before legacy logs and limit heuristic parsing to CLI dispatch lines. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
pelikhan · Oct 8, 2026 · Oct 8, 2026 · Oct 8, 2026 · Oct 8, 2026 · Oct 8, 2026
commit dfe18013924cc2cf144cd74e56b1053af1008079
diff --git a/.changeset/patch-unified-subagent-sessions.md b/.changeset/patch-unified-subagent-sessions.md
diff --git a/actions/setup/js/copilot_dynamic_workflow.test.cjs b/actions/setup/js/copilot_dynamic_workflow.test.cjs
@@ -8,6 +8,7 @@ import { normalizeUnifiedSessionEvent } from "./unified_session_payload.cjs";
 import { generatePlainTextSummary, generateCopilotCliStyleSummary } from "./log_parser_shared.cjs";
 import { runWithCopilotSDK } from "./copilot_sdk_session.cjs";
 import { projectSessionResult } from "./agent_session.cjs";
+import { createSessionValidator } from "./scripts/validate_session.cjs";
 
 const runId = "dynamic-smoke-run";
 const nativePath = "sandbox/agent/logs/copilot-session-state/root/events.jsonl";
@@ -40,6 +41,60 @@ describe("Copilot dynamic workflow sessions", () => {
     return root;
   };
 
+  it("collects exact per-agent accounting and attribution metadata into the unified file", () => {
+    const root = temporaryRoot();
+    const modelMetric = (count, totalNanoAiu) => ({
+      requests: { count, cost: 0 },
+      usage: { inputTokens: 100, outputTokens: 10, cacheReadTokens: 20, cacheWriteTokens: 30 },
+      totalNanoAiu,
+    });
+    const agentMetrics = {
+      main: { totalNanoAiu: 389122000000, modelMetrics: { opus: modelMetric(41, 389122000000) } },
+      research: { agentName: "research", agentDisplayName: "routing-research", totalNanoAiu: 494207000000, modelMetrics: { opus: modelMetric(45, 494207000000) } },
+      explore: { agentName: "explore", agentDisplayName: "routing-explore", totalNanoAiu: 9141000000, modelMetrics: { opus: modelMetric(3, 9141000000) } },
+    };
+    const native = [
+      { type: "session.start", data: { sessionId: "root", selectedModel: "opus", reasoningEffort: "xhigh" } },
+      {
+        type: "subagent.started",
+        agentId: "research",
+        data: {
+          toolCallId: "research-call",
+          agentName: "research",
+          agentDisplayName: "routing-research",
+          agentType: "built-in",
+          model: "opus",
+          modelSelectionSource: "agent_definition_default",
+          executionMode: "background",
+          agentDescription: "PRIVATE_PROMPT",
+        },
+      },
+      { type: "subagent.configured", agentId: "research", data: { model: "opus", reasoningEffort: "xhigh" } },
+      { type: "subagent.started", agentId: "explore", data: { parentId: "research", toolCallId: "explore-call", agentName: "explore", agentDisplayName: "routing-explore", model: "opus", executionMode: "sync" } },
+      { type: "subagent.configured", agentId: "explore", data: { model: "opus", reasoningEffort: "low" } },
+      { type: "session.model_change", agentId: "explore", data: { newModel: "opus", reasoningEffort: "low", source: "agent" } },
+      { type: "assistant.message", agentId: "explore", data: { content: "Done", model: "opus", apiCallId: "api-1", interactionId: "interaction-1", turnId: "turn-1", parentToolCallId: "explore-call", toolRequests: [] } },
+      { type: "subagent.completed", agentId: "explore", data: { model: "opus", firstDispatchedModel: "opus", totalTokens: 110, totalToolCalls: 1, durationMs: 100 } },
+      { type: "session.shutdown", data: { agentMetrics } },
+    ];
+    const parsed = parseCopilotLog(serialize(native)).logEntries;
+    expect(parsed.find(event => event.type === "session.result").data.agentMetrics).toEqual(agentMetrics);
+    const file = path.join(root, nativePath);
+    fs.mkdirSync(path.dirname(file), { recursive: true });
+    fs.writeFileSync(file, serialize(native));
+    const events = JSON.parse(JSON.stringify(collectUnifiedSession({ rootDir: root, engine: "copilot" }).events));
+    expect(events.find(event => event.type === "session.init").data).toMatchObject({ model: "opus", reasoningEffort: "xhigh" });
+    expect(events.find(event => event.type === "subagent.started" && event.agentId === "research").data).toMatchObject({ agentType: "built-in", modelSelectionSource: "agent_definition_default", executionMode: "background" });
+    expect(events.find(event => event.type === "subagent.started" && event.agentId === "explore").data.parentId).toBe("research");
+    expect(events.find(event => event.type === "subagent.configured" && event.agentId === "explore").data.reasoningEffort).toBe("low");
+    expect(events.find(event => event.type === "assistant.message").data).toMatchObject({ model: "opus", apiCallId: "api-1", interactionId: "interaction-1", turnId: "turn-1", parentToolCallId: "explore-call" });
+    expect(events.find(event => event.type === "subagent.completed").data.firstDispatchedModel).toBe("opus");
+    expect(events.find(event => event.type === "session.result").data.agentMetrics).toEqual(agentMetrics);
+    expect(events.find(event => event.type === "subagent.started").data).not.toHaveProperty("agentDescription");
+    const validate = createSessionValidator("unified").event;
+    for (const event of events) expect(validate(event), JSON.stringify(validate.errors)).toBe(true);
+  });
+
   it("retains native lifecycle signals and correlates subagents without conflating workflow accounting with session usage", () => {
     const original = structuredClone(lifecycle);
     const parsed = parseCopilotLog(serialize(lifecycle)).logEntries;

diff --git a/actions/setup/js/copilot_session.cjs b/actions/setup/js/copilot_session.cjs
@@ -228,6 +228,7 @@ function normalizeCopilotSession(entries) {
       const end = typeof event.timestamp === "string" ? Date.parse(event.timestamp) : event.timestamp;
       if (typeof end === "number" && isMetric(data.sessionStartTime) && isMetric(end) && end >= data.sessionStartTime) result.durationMs = end - data.sessionStartTime;
       if (data.errorReason !== undefined) result.errors = [data.errorReason];
+      if (data.agentMetrics !== undefined) result.agentMetrics = structuredClone(data.agentMetrics);
       if (Object.keys(result).length) project("session.result", result);
     } else if (event.type === "session.error") {
       project("session.result", { errors: [data.error !== undefined ? structuredClone(data.error) : structuredClone(data)] });

diff --git a/actions/setup/js/copilot_workflow_events.cjs b/actions/setup/js/copilot_workflow_events.cjs
@@ -17,8 +17,10 @@ const COPILOT_WORKFLOW_EVENT_FIELDS = {
     toolCallId: ["toolCallId"],
     agentName: ["agentName"],
     agentDisplayName: ["agentDisplayName"],
+    agentType: ["agentType"],
     parentId: ["parentId"],
     model: ["model"],
+    modelSelectionSource: ["modelSelectionSource"],
     executionMode: ["executionMode"],
   },
   "subagent.configured": { model: ["model"], contextTier: ["contextTier"], reasoningEffort: ["reasoningEffort"], multiTurn: ["multiTurn"] },
@@ -27,6 +29,7 @@ const COPILOT_WORKFLOW_EVENT_FIELDS = {
     agentName: ["agentName"],
     agentDisplayName: ["agentDisplayName"],
     model: ["model"],
+    firstDispatchedModel: ["firstDispatchedModel"],
     durationMs: ["durationMs"],
     totalTokens: ["totalTokens"],
     totalToolCalls: ["totalToolCalls"],

diff --git a/actions/setup/js/types/agent_session.d.ts b/actions/setup/js/types/agent_session.d.ts
@@ -37,6 +37,7 @@ export interface EventMetadata {
 export interface SessionInitData {
   sourceEngine?: string;
   model?: string;
+  reasoningEffort?: string;
   sessionId?: string | null;
   cwd?: string;
   tools?: JsonValue[];
@@ -118,6 +119,8 @@ export interface SessionResultData {
   usage?: SessionUsage;
   errors?: JsonValue[];
   permissionDenials?: JsonValue[];
+  /** Exact per-agent accounting snapshot supplied by the engine, not additive usage. */
+  agentMetrics?: JsonValue;
   [key: string]: unknown;
 }
 

diff --git a/actions/setup/js/types/unified_session.d.ts b/actions/setup/js/types/unified_session.d.ts
@@ -29,10 +29,26 @@ export interface UnifiedSessionUsage {
   overflowedTokens?: string[];
 }
 
-export interface UnifiedSessionResultData extends Pick<SessionResultData, "numTurns" | "durationMs" | "totalCostUsd" | "status" | "sourceType" | "errors" | "permissionDenials"> {
+export interface UnifiedSessionResultData extends Pick<SessionResultData, "numTurns" | "durationMs" | "totalCostUsd" | "status" | "sourceType" | "errors" | "permissionDenials" | "agentMetrics"> {
   usage?: UnifiedSessionUsage | null;
 }
 
+export interface UnifiedMessageData extends Pick<MessageData, "content"> {
+  delta?: JsonValue;
+  partial?: JsonValue;
+  messageId?: JsonValue;
+  contentIndex?: JsonValue;
+  channel?: JsonValue;
+  sessionId?: JsonValue;
+  agentId?: JsonValue;
+  parentToolUseId?: JsonValue;
+  model?: JsonValue;
+  apiCallId?: JsonValue;
+  interactionId?: JsonValue;
+  turnId?: JsonValue;
+  parentToolCallId?: JsonValue;
+}
+
 export interface DynamicWorkflowTaskData {
   taskId?: string;
   toolCallId?: string;
@@ -249,14 +265,14 @@ export interface CollectionData {
 export interface UnifiedSessionEventDataMap {
   "session.format": SessionFileFormatData;
   "agent.execution": AgentExecutionData;
-  "session.init": Pick<SessionInitData, "sourceEngine" | "model" | "sessionId" | "cwd">;
-  "session.start": Pick<SessionInitData, "sourceEngine" | "model" | "sessionId" | "cwd">;
+  "session.init": Pick<SessionInitData, "sourceEngine" | "model" | "sessionId" | "cwd" | "reasoningEffort">;
+  "session.start": Pick<SessionInitData, "sourceEngine" | "model" | "sessionId" | "cwd" | "reasoningEffort">;
   "user.message": Pick<MessageData, "content">;
   "prompt.system": Pick<MessageData, "content">;
   "prompt.user": Pick<MessageData, "content">;
-  "assistant.message": Pick<MessageData, "content">;
+  "assistant.message": UnifiedMessageData;
   "assistant.refusal": Pick<AssistantRefusalData, "reason" | "content" | "policyCategory" | "explanation" | "partial">;
-  "assistant.reasoning": Pick<MessageData, "content">;
+  "assistant.reasoning": UnifiedMessageData;
   "tool.execution_start": Pick<ToolExecutionStartData, "toolCallId" | "toolName" | "input" | "command" | "mcpServerName">;
   "tool.execution_complete": Pick<
     ToolExecutionCompleteData,

diff --git a/actions/setup/js/unified_session_payload.cjs b/actions/setup/js/unified_session_payload.cjs
@@ -88,6 +88,11 @@ const MESSAGE_FIELDS = {
   sessionId: ["sessionId", "session_id"],
   agentId: ["agentId"],
   parentToolUseId: ["parentToolUseId", "parent_tool_use_id"],
+  model: ["model"],
+  apiCallId: ["apiCallId"],
+  interactionId: ["interactionId"],
+  turnId: ["turnId"],
+  parentToolCallId: ["parentToolCallId"],
 };
 
 /** @type {Fields} */
@@ -106,7 +111,7 @@ const EVENT_FIELDS = {
   ...COPILOT_WORKFLOW_EVENT_FIELDS,
   "session.format": { version: ["version"] },
   "agent.execution": { categories: ["categories"], errorCodes: ["errorCodes"], errorTypes: ["errorTypes"], exitCode: ["exitCode", "exit_code"] },
-  "session.init": { sourceEngine: ["sourceEngine"], model: ["model"], sessionId: ["sessionId", "session_id"], cwd: ["cwd"] },
+  "session.init": { sourceEngine: ["sourceEngine"], model: ["model", "selectedModel"], sessionId: ["sessionId", "session_id"], cwd: ["cwd"], reasoningEffort: ["reasoningEffort"] },
   "user.message": { content: ["content"] },
   "prompt.system": { content: ["content"] },
   "prompt.user": { content: ["content"] },
@@ -136,6 +141,7 @@ const EVENT_FIELDS = {
     sourceType: ["sourceType"],
     errors: ["errors"],
     permissionDenials: ["permissionDenials", "permission_denials"],
+    agentMetrics: ["agentMetrics"],
   },
   "mcp.rpc.request": MCP_FIELDS,
   "mcp.rpc.response": MCP_FIELDS,

diff --git a/actions/setup/js/unified_session_payload.test.cjs b/actions/setup/js/unified_session_payload.test.cjs
@@ -104,7 +104,7 @@ describe("essential unified session payloads", () => {
     };
     const original = structuredClone(message);
     const compact = normalizeUnifiedSessionEvent(message);
-    expect(compact).toEqual({ type: "assistant.message", id: "message", parentId: null, timestamp: message.timestamp, data: { content } });
+    expect(compact).toEqual({ type: "assistant.message", id: "message", parentId: null, timestamp: message.timestamp, data: { content, model: "duplicated" } });
     expect(Buffer.byteLength(JSON.stringify(compact))).toBeLessThan(Buffer.byteLength(JSON.stringify(message)) / 2);
     expect(message).toEqual(original);
     expect(normalizeUnifiedSessionEvent(compact)).toEqual(compact);

diff --git a/docs/public/schemas/agent-session.schema.json b/docs/public/schemas/agent-session.schema.json
@@ -81,6 +81,7 @@
       "properties": {
         "sourceEngine": { "type": "string" },
         "model": { "type": "string" },
+        "reasoningEffort": { "type": "string" },
         "sessionId": { "type": ["string", "null"] },
         "cwd": { "type": "string" },
         "tools": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } },
@@ -101,7 +102,8 @@
         "sourceType": { "type": "string" },
         "usage": { "$ref": "#/definitions/SessionUsage" },
         "errors": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } },
-        "permissionDenials": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } }
+        "permissionDenials": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } },
+        "agentMetrics": { "$ref": "#/definitions/JsonValue", "description": "Exact per-agent accounting snapshot supplied by the engine, not additive usage." }
       },
       "additionalProperties": {}
     },

diff --git a/docs/public/schemas/unified-session.schema.json b/docs/public/schemas/unified-session.schema.json
@@ -11,8 +11,8 @@
     "allOf": [
       { "$ref": "#/definitions/EventMetadata" },
       { "if": { "properties": { "type": { "const": "agent.execution" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/AgentExecutionData" } } } },
-      { "if": { "properties": { "type": { "const": "assistant.message" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CMessageData%2C%22content%22%3E" } } } },
-      { "if": { "properties": { "type": { "const": "assistant.reasoning" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CMessageData%2C%22content%22%3E" } } } },
+      { "if": { "properties": { "type": { "const": "assistant.message" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/UnifiedMessageData" } } } },
+      { "if": { "properties": { "type": { "const": "assistant.reasoning" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/UnifiedMessageData" } } } },
       {
         "if": { "properties": { "type": { "const": "assistant.refusal" } }, "required": ["type"] },
         "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CAssistantRefusalData%2C(%22reason%22%7C%22content%22%7C%22policyCategory%22%7C%22explanation%22%7C%22partial%22)%3E" } } }
@@ -52,12 +52,12 @@
       { "if": { "properties": { "type": { "const": "session.format" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/SessionFileFormatData" } } } },
       {
         "if": { "properties": { "type": { "const": "session.init" } }, "required": ["type"] },
-        "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CSessionInitData%2C(%22sourceEngine%22%7C%22model%22%7C%22sessionId%22%7C%22cwd%22)%3E" } } }
+        "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CSessionInitData%2C(%22sourceEngine%22%7C%22model%22%7C%22sessionId%22%7C%22cwd%22%7C%22reasoningEffort%22)%3E" } } }
       },
       { "if": { "properties": { "type": { "const": "session.result" } }, "required": ["type"] }, "then": { "properties": { "data": { "$ref": "#/definitions/UnifiedSessionResultData" } } } },
       {
         "if": { "properties": { "type": { "const": "session.start" } }, "required": ["type"] },
-        "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CSessionInitData%2C(%22sourceEngine%22%7C%22model%22%7C%22sessionId%22%7C%22cwd%22)%3E" } } }
+        "then": { "properties": { "data": { "$ref": "#/definitions/Pick%3CSessionInitData%2C(%22sourceEngine%22%7C%22model%22%7C%22sessionId%22%7C%22cwd%22%7C%22reasoningEffort%22)%3E" } } }
       },
       {
         "if": { "properties": { "type": { "const": "tool.execution_complete" } }, "required": ["type"] },
@@ -347,9 +347,9 @@
       "additionalProperties": false
     },
     "Pick<MessageData,\"content\">": { "type": "object", "properties": { "content": { "$ref": "#/definitions/JsonValue" } }, "additionalProperties": false },
-    "Pick<SessionInitData,(\"sourceEngine\"|\"model\"|\"sessionId\"|\"cwd\")>": {
+    "Pick<SessionInitData,(\"sourceEngine\"|\"model\"|\"sessionId\"|\"cwd\"|\"reasoningEffort\")>": {
       "type": "object",
-      "properties": { "sourceEngine": { "type": "string" }, "model": { "type": "string" }, "sessionId": { "type": ["string", "null"] }, "cwd": { "type": "string" } },
+      "properties": { "sourceEngine": { "type": "string" }, "model": { "type": "string" }, "sessionId": { "type": ["string", "null"] }, "cwd": { "type": "string" }, "reasoningEffort": { "type": "string" } },
       "additionalProperties": false
     },
     "Pick<ToolExecutionCompleteData,(\"toolCallId\"|\"toolName\"|\"success\"|\"output\"|\"error\"|\"durationMs\"|\"exitCode\"|\"status\"|\"mcpServerName\"|\"isError\"|\"taskId\"|\"taskType\"|\"workflowName\"|\"workflowRunId\")>": {
@@ -446,6 +446,26 @@
       "additionalProperties": false,
       "description": "Collector metadata is separate from native engine event metadata."
     },
+    "UnifiedMessageData": {
+      "type": "object",
+      "properties": {
+        "content": { "$ref": "#/definitions/JsonValue" },
+        "delta": { "$ref": "#/definitions/JsonValue" },
+        "partial": { "$ref": "#/definitions/JsonValue" },
+        "messageId": { "$ref": "#/definitions/JsonValue" },
+        "contentIndex": { "$ref": "#/definitions/JsonValue" },
+        "channel": { "$ref": "#/definitions/JsonValue" },
+        "sessionId": { "$ref": "#/definitions/JsonValue" },
+        "agentId": { "$ref": "#/definitions/JsonValue" },
+        "parentToolUseId": { "$ref": "#/definitions/JsonValue" },
+        "model": { "$ref": "#/definitions/JsonValue" },
+        "apiCallId": { "$ref": "#/definitions/JsonValue" },
+        "interactionId": { "$ref": "#/definitions/JsonValue" },
+        "turnId": { "$ref": "#/definitions/JsonValue" },
+        "parentToolCallId": { "$ref": "#/definitions/JsonValue" }
+      },
+      "additionalProperties": false
+    },
     "UnifiedSessionResultData": {
       "type": "object",
       "properties": {
@@ -456,6 +476,7 @@
         "sourceType": { "type": "string" },
         "errors": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } },
         "permissionDenials": { "type": "array", "items": { "$ref": "#/definitions/JsonValue" } },
+        "agentMetrics": { "$ref": "#/definitions/JsonValue", "description": "Exact per-agent accounting snapshot supplied by the engine, not additive usage." },
         "usage": { "anyOf": [{ "$ref": "#/definitions/UnifiedSessionUsage" }, { "type": "null" }] }
       },
       "additionalProperties": false