Coarsen message stream diagnostics

src/features/chat/app-server/mappers/message-stream/turn-items.ts

@@ -1,8 +1,8 @@
-import type { CommandMessageStreamTarget, MessageStreamItem } from "../../../domain/message-stream/items";
+import type { CommandMessageStreamTarget, MessageStreamDiagnosticSection, MessageStreamItem } from "../../../domain/message-stream/items";
 import type { MessageStreamItemProvenance } from "../../../domain/message-stream/provenance";
 import type { HistoricalTurn } from "../../../../../domain/threads/history";
 import type { TurnItem } from "../../../../../app-server/protocol/turn";
-import { definedProp } from "../../../../../utils";
+import { definedProp, jsonPreview } from "../../../../../utils";
 import { referencedThreadMetadataFromPrompt } from "../../../../../domain/threads/reference";
 import { turnUserItemText } from "../../../../../app-server/protocol/turn";
 import { agentMessageStreamItem } from "./agent-items";
@@ -201,11 +201,14 @@ function mcpToolCallMessageStreamItem(item: McpToolCallItem, turnId?: string): M
     ...(target ? { primaryTarget: { kind: "value" as const, value: target } } : {}),
     ...(item.error?.message ? { failureReason: item.error.message } : {}),
     status: item.status,
-    toolCall: {
-      arguments: item.arguments,
-      result: item.result,
-      error: item.error,
-    },
+    ...definedProp(
+      "diagnostics",
+      jsonDiagnosticSections(
+        { title: "Arguments JSON", value: item.arguments },
+        { title: "Result JSON", value: item.result },
+        { title: "Error JSON", value: item.error },
+      ),
+    ),
     output: "",
     executionState: mcpToolCallExecutionState(item.status),
   };
@@ -223,10 +226,10 @@ function dynamicToolCallMessageStreamItem(item: DynamicToolCallItem, turnId?: st
     ...(target ? { primaryTarget: { kind: "value" as const, value: target } } : {}),
     ...(failure ? { failureReason: failure } : {}),
     status: item.status,
-    toolCall: {
-      arguments: item.arguments,
-      result: item.contentItems,
-    },
+    ...definedProp(
+      "diagnostics",
+      jsonDiagnosticSections({ title: "Arguments JSON", value: item.arguments }, { title: "Result JSON", value: item.contentItems }),
+    ),
     output: "",
     executionState: dynamicToolCallExecutionState(item.status, item.success),
   };
@@ -502,6 +505,15 @@ function jsonTargetLabel(value: unknown): string | null {
   return firstEntry ? jsonTargetPrimitive(firstEntry[1]) : null;
 }
 
+function jsonDiagnosticSections(
+  ...sections: readonly { readonly title: string; readonly value: unknown }[]
+): readonly MessageStreamDiagnosticSection[] | undefined {
+  const diagnostics = sections
+    .filter((section) => section.value !== null && section.value !== undefined)
+    .map((section) => ({ title: section.title, body: jsonPreview(section.value) }));
+  return diagnostics.length > 0 ? diagnostics : undefined;
+}
+
 function jsonTargetPrimitive(value: unknown): string | null {
   if (typeof value === "string" && value.trim().length > 0) return value.trim();
   if (typeof value === "number" || typeof value === "boolean") return String(value);

src/features/chat/domain/message-stream/items.ts

@@ -41,10 +41,9 @@ export type MessageStreamPrimaryTarget =
       readonly value: string;
     };
 
-interface MessageStreamToolCallDetails {
-  readonly arguments?: unknown;
-  readonly result?: unknown;
-  readonly error?: unknown;
+export interface MessageStreamDiagnosticSection {
+  readonly title: string;
+  readonly body: string;
 }
 
 interface MessageStreamWebSearchDetails {
@@ -227,7 +226,7 @@ interface ToolMessageStreamBase extends MessageStreamBase {
 
 export interface ToolCallMessageStreamItem extends ToolMessageStreamBase {
   readonly kind: "tool";
-  readonly toolCall?: MessageStreamToolCallDetails;
+  readonly diagnostics?: readonly MessageStreamDiagnosticSection[];
   readonly webSearch?: MessageStreamWebSearchDetails;
   readonly imageGeneration?: MessageStreamImageGenerationDetails;
 }

src/features/chat/presentation/message-stream/detail-view.ts

@@ -1,4 +1,4 @@
-import { jsonPreview, shortThreadId, truncate } from "../../../../utils";
+import { shortThreadId, truncate } from "../../../../utils";
 import { failedStatusLabel } from "../../domain/message-stream/execution-state";
 import { pathRelativeToRoot } from "../../domain/message-stream/format/path-labels";
 import type {
@@ -265,7 +265,7 @@ function resultDetails(item: ApprovalResultMessageStreamItem | ReviewResultMessa
 
 function genericToolDetails(item: ToolCallMessageStreamItem | HookMessageStreamItem): DetailSection[] {
   if (item.kind === "hook") return hookRunDetails(item);
-  return [...toolCallDetails(item), ...webSearchDetails(item), ...imageGenerationDetails(item)];
+  return [...diagnosticDetails(item), ...webSearchDetails(item), ...imageGenerationDetails(item)];
 }
 
 function genericDetailSections(item: MessageStreamItem, workspaceRoot?: string | null): DetailSection[] {
@@ -279,14 +279,8 @@ function genericDetailSections(item: MessageStreamItem, workspaceRoot?: string |
   return [...(rows.length > 0 ? [{ kind: "kv" as const, rows }] : []), ...outputSection("Output", outputField(item))];
 }
 
-function toolCallDetails(item: ToolCallMessageStreamItem): DetailSection[] {
-  const details = item.toolCall;
-  if (!details) return [];
-  return [
-    ...jsonOutputSection("Arguments JSON", details.arguments),
-    ...jsonOutputSection("Result JSON", details.result),
-    ...jsonOutputSection("Error JSON", details.error),
-  ];
+function diagnosticDetails(item: ToolCallMessageStreamItem): DetailSection[] {
+  return item.diagnostics?.map((section) => ({ kind: "output" as const, title: section.title, body: section.body })) ?? [];
 }
 
 function webSearchDetails(item: ToolCallMessageStreamItem): DetailSection[] {
@@ -328,10 +322,6 @@ function outputSection(title: string, body: string | null | undefined): DetailSe
   return body ? [{ kind: "output", title, body }] : [];
 }
 
-function jsonOutputSection(title: string, value: unknown): DetailSection[] {
-  return value === null || value === undefined ? [] : outputSection(title, jsonPreview(value));
-}
-
 function metaRow(key: string, value: string | null | undefined): { key: string; value: string }[] {
   return value ? [{ key, value }] : [];
 }

tests/features/chat/message-stream/model.test.ts

@@ -636,10 +636,10 @@ describe("turn item conversion preserves app-server semantics", () => {
       primaryTarget: { kind: "value", value: "123" },
       failureReason: "Not found",
       toolName: "github.pull_request_read",
-      toolCall: {
-        arguments: expect.objectContaining({ id: 123 }),
-        error: { message: "Not found" },
-      },
+      diagnostics: expect.arrayContaining([
+        { title: "Arguments JSON", body: expect.stringContaining('"id": 123') },
+        { title: "Error JSON", body: expect.stringContaining("Not found") },
+      ]),
       executionState: "failed",
     });
   });
@@ -661,10 +661,10 @@ describe("turn item conversion preserves app-server semantics", () => {
       kind: "tool",
       primaryTarget: { kind: "value", value: "https://example.com" },
       toolName: "web.open",
-      toolCall: {
-        arguments: { url: "https://example.com" },
-        result: [{ type: "inputText", text: "ok" }],
-      },
+      diagnostics: expect.arrayContaining([
+        { title: "Arguments JSON", body: expect.stringContaining("https://example.com") },
+        { title: "Result JSON", body: expect.stringContaining("inputText") },
+      ]),
       executionState: "completed",
     });
   });

tests/features/chat/message-stream/semantics.test.ts

@@ -76,7 +76,7 @@ describe("message stream semantic classification", () => {
         changes: [{ kind: "update", path: "src/main.ts", diff: "@@" }],
         executionState: "completed",
       },
-      { id: "tool", kind: "tool", role: "tool", text: "tool", toolCall: { arguments: { k: "v" } } },
+      { id: "tool", kind: "tool", role: "tool", text: "tool", diagnostics: [{ title: "Arguments JSON", body: '{"k":"v"}' }] },
       { id: "hook", kind: "hook", role: "tool", text: "hook" },
       { id: "reasoning", kind: "reasoning", role: "tool", text: "thinking" },
       { id: "wait", kind: "wait", role: "tool", text: "Waited 2.5s", executionState: "completed" },

tests/features/chat/ui/message-stream/stream-items.test.tsx

@@ -33,10 +33,10 @@ describe("message stream item renderer decisions", () => {
           toolName: "github.pull_request_read",
           turnId: "turn",
           status: "completed",
-          toolCall: {
-            arguments: { id: 123 },
-            result: { ok: true },
-          },
+          diagnostics: [
+            { title: "Arguments JSON", body: '{\n  "id": 123\n}' },
+            { title: "Result JSON", body: '{\n  "ok": true\n}' },
+          ],
         },
       ],
       disclosures: emptyDisclosures(),