diff --git a/packages/frontend/editor-ui/src/features/agents/__tests__/AgentChatMessageList.test.ts b/packages/frontend/editor-ui/src/features/agents/__tests__/AgentChatMessageList.test.ts
index fddb95db668..7d169daaa66 100644
--- a/packages/frontend/editor-ui/src/features/agents/__tests__/AgentChatMessageList.test.ts
+++ b/packages/frontend/editor-ui/src/features/agents/__tests__/AgentChatMessageList.test.ts
@@ -4,6 +4,12 @@ import { h } from 'vue';
 import AgentChatMessageList from '../components/AgentChatMessageList.vue';
 import type { ChatMessage, ToolCall } from '@/features/ai/shared/agentsChat/types';
 import { planMessage, planTask, planView } from './fixtures/agent-plan';
+import { computed } from 'vue';
+import { AGENTS_CHAT_INTERACTION_EXTENSIONS } from '@/features/ai/shared/agentsChat/interactionRegistry';
+import {
+	TEST_RESULT_TOOL_NAME,
+	testToolResultExtension,
+} from '@/features/ai/shared/agentsChat/__tests__/fixtures/testInteractionExtension';
 
 const copySpy = vi.fn();
 
@@ -1384,4 +1390,118 @@ describe('AgentChatMessageList', () => {
 			expect(wrapper.findAll('[data-testid="agent-chat-timestamp-divider"]')).toHaveLength(0);
 		});
 	});
+	describe('host tool-result renderers', () => {
+		const savedNote: ToolCall = {
+			tool: TEST_RESULT_TOOL_NAME,
+			toolCallId: 'tc-note',
+			state: 'done',
+			input: { text: 'Remember this' },
+			output: { saved: true },
+		};
+		const httpCall: ToolCall = {
+			tool: 'http_request',
+			toolCallId: 'tc-http',
+			state: 'done',
+			output: { status: 200 },
+		};
+
+		function assistantMessage(toolCalls: ToolCall[], content = ''): ChatMessage {
+			return { id: 'assistant-1', role: 'assistant', content, toolCalls, status: 'success' };
+		}
+
+		function mountList(messages: ChatMessage[], withExtension = true) {
+			return mount(AgentChatMessageList, {
+				props: { messages, messagingState: 'idle' },
+				global: withExtension
+					? {
+							provide: {
+								[AGENTS_CHAT_INTERACTION_EXTENSIONS]: computed(() => [testToolResultExtension]),
+							},
+						}
+					: {},
+			});
+		}
+
+		function stepToolCallIds(wrapper: ReturnType<typeof mountList>): string[] {
+			return wrapper
+				.findAllComponents({ name: 'AgentChatToolSteps' })
+				.flatMap((steps) => (steps.props('toolCalls') as ToolCall[]).map((tc) => tc.toolCallId));
+		}
+
+		it.each([
+			['a tool run', ''],
+			['a message with text', 'Saved your note.'],
+		])('renders the host component in place of the default step in %s', (_, content) => {
+			const wrapper = mountList([assistantMessage([httpCall, savedNote], content)]);
+
+			const results = wrapper.findAll('[data-testid="agent-chat-host-tool-result"]');
+			expect(results).toHaveLength(1);
+			expect(results[0].find('[data-testid="test-tool-result"]').text()).toContain('tc-note');
+			expect(results[0].text()).toContain('{"saved":true}');
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-http']);
+			wrapper.unmount();
+		});
+
+		it('hides the tool steps when the host renders every call', () => {
+			const wrapper = mountList([assistantMessage([savedNote])]);
+
+			expect(wrapper.findAll('[data-testid="test-tool-result"]')).toHaveLength(1);
+			expect(wrapper.findComponent({ name: 'AgentChatToolSteps' }).exists()).toBe(false);
+			wrapper.unmount();
+		});
+
+		it('renders the default step without extensions', () => {
+			const wrapper = mountList([assistantMessage([httpCall, savedNote])], false);
+
+			expect(wrapper.find('[data-testid="agent-chat-host-tool-result"]').exists()).toBe(false);
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-http', 'tc-note']);
+			wrapper.unmount();
+		});
+
+		it('falls back to the default step until the call finishes', async () => {
+			const running: ToolCall = { ...savedNote, state: 'running', output: undefined };
+			const wrapper = mountList([assistantMessage([running])]);
+
+			expect(wrapper.find('[data-testid="test-tool-result"]').exists()).toBe(false);
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-note']);
+
+			await wrapper.setProps({ messages: [assistantMessage([savedNote])] });
+
+			expect(wrapper.findAll('[data-testid="test-tool-result"]')).toHaveLength(1);
+			expect(stepToolCallIds(wrapper)).toEqual([]);
+			wrapper.unmount();
+		});
+
+		it('falls back to the default step until the output arrives', () => {
+			const ended: ToolCall = { ...savedNote, output: undefined };
+			const wrapper = mountList([assistantMessage([ended])]);
+
+			expect(wrapper.find('[data-testid="test-tool-result"]').exists()).toBe(false);
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-note']);
+			wrapper.unmount();
+		});
+
+		it('keeps the default step for a suspended copy of a call that finished later', () => {
+			const suspended: ToolCall = { ...savedNote, state: 'suspended', output: undefined };
+			const wrapper = mountList([
+				{ ...assistantMessage([suspended], 'Saving your note.'), id: 'assistant-1' },
+				{ ...assistantMessage([savedNote]), id: 'assistant-2' },
+			]);
+
+			const results = wrapper.findAll('[data-testid="test-tool-result"]');
+			expect(results).toHaveLength(1);
+			expect(results[0].text()).toContain('{"saved":true}');
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-note']);
+			wrapper.unmount();
+		});
+
+		it('falls back to the default step for a failed call', () => {
+			const failed: ToolCall = { ...savedNote, state: 'error', output: 'boom' };
+			const wrapper = mountList([assistantMessage([failed])]);
+
+			expect(wrapper.find('[data-testid="test-tool-result"]').exists()).toBe(false);
+			expect(stepToolCallIds(wrapper)).toEqual(['tc-note']);
+			wrapper.unmount();
+		});
+	});
 });
diff --git a/packages/frontend/editor-ui/src/features/agents/components/AgentChatMessageList.vue b/packages/frontend/editor-ui/src/features/agents/components/AgentChatMessageList.vue
index 477585b4052..d2bf30301cc 100644
--- a/packages/frontend/editor-ui/src/features/agents/components/AgentChatMessageList.vue
+++ b/packages/frontend/editor-ui/src/features/agents/components/AgentChatMessageList.vue
@@ -1,13 +1,22 @@
 <script setup lang="ts">
-import { computed, nextTick, onMounted, ref, useTemplateRef, watch } from 'vue';
+import { computed, inject, nextTick, onMounted, ref, useTemplateRef, watch } from 'vue';
 import { N8nButton, N8nCallout, N8nIcon, N8nIconButton, N8nText } from '@n8n/design-system';
 import { APPROVAL_TOOL_NAME, N8N_CHAT_ACTION_TOOL_NAME } from '@n8n/api-types';
 import { isAwaitingCard } from '@/features/ai/shared/agentsChat/n8nChatInteraction';
 import { useI18n } from '@n8n/i18n';
 import { useSessionStorage } from '@vueuse/core';
 import { TIME } from '@/app/constants/durations';
-import { isAssistantGroup, type DisplayGroup } from '@/features/ai/shared/agentsChat/displayGroups';
+import {
+	DISPLAY_GROUP_KIND,
+	isAssistantGroup,
+	type DisplayGroup,
+} from '@/features/ai/shared/agentsChat/displayGroups';
 import { getMessageInteractives, isRecord } from '@/features/ai/shared/agentsChat/messageMappers';
+import {
+	AGENTS_CHAT_INTERACTION_EXTENSIONS,
+	findToolResultRenderer,
+	type AgentsChatToolResultRenderer,
+} from '@/features/ai/shared/agentsChat/interactionRegistry';
 import {
 	getMessageThinkingSegments,
 	getThinkingDurationSec,
@@ -68,8 +77,9 @@ const canSendToAssistant = computed(() =>
 );
 
 function onFixWithAssistant(group: DisplayGroup, failures: AgentFixWithAssistantFailure[]) {
-	if (group.kind === 'backgroundJobSignal') return;
-	const executionId = group.kind === 'toolRun' ? group.executionId : group.message.executionId;
+	if (group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL) return;
+	const executionId =
+		group.kind === DISPLAY_GROUP_KIND.TOOL_RUN ? group.executionId : group.message.executionId;
 	if (!executionId || failures.length === 0) return;
 	emit('sendToAssistant', { executionId, failures });
 }
@@ -157,9 +167,50 @@ function getMessageRenderItems(message: ChatMessage): MessageRenderItem[] {
 	return items;
 }
 
+const interactionExtensions = inject(AGENTS_CHAT_INTERACTION_EXTENSIONS, undefined);
+
 const scrollRef = useTemplateRef<HTMLDivElement>('scrollRef');
 
 const displayGroups = computed(() => buildAgentPlanDisplayGroups(props.messages));
+interface GroupToolCalls {
+	/** Calls that render as default tool steps. */
+	steps: ToolCall[];
+	/** Finished calls that a host extension renders in place of a step. */
+	hostResults: Array<{ toolCall: ToolCall; renderer: AgentsChatToolResultRenderer }>;
+}
+
+const NO_GROUP_TOOL_CALLS: GroupToolCalls = { steps: [], hostResults: [] };
+
+/**
+ * The tool calls of each group, split into default steps and host results.
+ * History can hold the same `toolCallId` twice (suspended, then resolved), so
+ * each group checks its own copy of the call.
+ */
+const toolCallsByGroupId = computed(() => {
+	const extensions = interactionExtensions?.value ?? [];
+	const byGroupId = new Map<string, GroupToolCalls>();
+	for (const group of displayGroups.value) {
+		if (group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL) continue;
+		const toolCalls =
+			group.kind === DISPLAY_GROUP_KIND.TOOL_RUN
+				? group.toolCalls
+				: (group.message.toolCalls ?? []);
+		const split: GroupToolCalls = { steps: [], hostResults: [] };
+		for (const toolCall of toolCalls) {
+			const renderer =
+				extensions.length > 0 ? findToolResultRenderer(toolCall, extensions) : undefined;
+			if (renderer) split.hostResults.push({ toolCall, renderer });
+			else split.steps.push(toolCall);
+		}
+		byGroupId.set(group.id, split);
+	}
+	return byGroupId;
+});
+
+function getGroupToolCalls(groupId: string): GroupToolCalls {
+	return toolCallsByGroupId.value.get(groupId) ?? NO_GROUP_TOOL_CALLS;
+}
+
 const retryErrorMessageId = computed(() => {
 	const message = props.messages.at(-1);
 	return props.retryMessageId && isRetryableChatError(message) ? message?.id : undefined;
@@ -182,7 +233,7 @@ const dividerLabels = computed(() => {
 	const labels = new Map<string, string>();
 	let previousUserCreatedAt: number | undefined;
 	for (const group of displayGroups.value) {
-		if (group.kind !== 'message' || group.message.role !== 'user') continue;
+		if (group.kind !== DISPLAY_GROUP_KIND.MESSAGE || group.message.role !== 'user') continue;
 		const createdAt = group.message.createdAt;
 		if (createdAt === undefined) continue;
 		// A new local day always earns a divider, even inside the window: without
@@ -219,7 +270,7 @@ const changeRequestGroupId = computed(() =>
 	canSendToAssistant.value && !changeNoteDismissed.value
 		? displayGroups.value.findLast(
 				(group) =>
-					group.kind === 'message' &&
+					group.kind === DISPLAY_GROUP_KIND.MESSAGE &&
 					group.message.role === 'user' &&
 					looksLikeAgentChangeRequest(group.message.content),
 			)?.id
@@ -238,8 +289,8 @@ function isThinkingActive(message: ChatMessage): boolean {
 }
 
 function getAssistantGroupContent(group: DisplayGroup): string {
-	if (group.kind === 'backgroundJobSignal') return '';
-	if (group.kind === 'toolRun') {
+	if (group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL) return '';
+	if (group.kind === DISPLAY_GROUP_KIND.TOOL_RUN) {
 		return group.finalMessage?.content ?? '';
 	}
 
@@ -306,8 +357,8 @@ function parseMemoryOutput(output: unknown): MemoryUsed[] {
 }
 
 function isCompletedAssistantGroup(group: DisplayGroup): boolean {
-	if (group.kind === 'backgroundJobSignal') return false;
-	if (group.kind === 'toolRun') {
+	if (group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL) return false;
+	if (group.kind === DISPLAY_GROUP_KIND.TOOL_RUN) {
 		return (
 			group.finalMessage !== undefined &&
 			group.finalMessage.status !== CHAT_MESSAGE_STATUS.STREAMING &&
@@ -344,7 +395,10 @@ function getMemoriesUsedInAssistantRun(groupId: string): MemoryUsed[] {
 		const group = displayGroups.value[i];
 		if (!isAssistantGroup(group)) break;
 
-		const toolCalls = group.kind === 'toolRun' ? group.toolCalls : (group.message.toolCalls ?? []);
+		const toolCalls =
+			group.kind === DISPLAY_GROUP_KIND.TOOL_RUN
+				? group.toolCalls
+				: (group.message.toolCalls ?? []);
 		for (let j = toolCalls.length - 1; j >= 0; j--) {
 			const toolCall = toolCalls[j];
 			if (toolCall.tool !== 'recall_memory') continue;
@@ -471,20 +525,34 @@ watch(
 			>
 				<N8nText size="small" color="text-light">{{ dividerLabels.get(group.id) }}</N8nText>
 			</div>
-			<div v-if="group.kind === 'backgroundJobSignal'" :class="[$style.message, $style.assistant]">
+			<div
+				v-if="group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL"
+				:class="[$style.message, $style.assistant]"
+			>
 				<AgentChatBackgroundJobSignal :class="$style.content" :signal="group.signal" />
 			</div>
-			<div v-else-if="group.kind === 'toolRun'" :class="[$style.message, $style.assistant]">
+			<div
+				v-else-if="group.kind === DISPLAY_GROUP_KIND.TOOL_RUN"
+				:class="[$style.message, $style.assistant]"
+			>
 				<div :class="$style.content">
 					<AgentChatToolSteps
-						v-if="group.toolCalls.length"
-						:tool-calls="group.toolCalls"
+						v-if="getGroupToolCalls(group.id).steps.length"
+						:tool-calls="getGroupToolCalls(group.id).steps"
 						:project-id="projectId"
 						:can-fix-with-assistant="canSendToAssistant"
 						:dismissed-tool-call-ids="dismissedFixToolCallIds"
 						:execution-id="group.executionId"
 						@fix-with-assistant="onFixWithAssistant(group, $event)"
 					/>
+					<div
+						v-for="result in getGroupToolCalls(group.id).hostResults"
+						:key="`result-${result.toolCall.toolCallId}`"
+						:class="$style.toolResult"
+						data-testid="agent-chat-host-tool-result"
+					>
+						<component :is="result.renderer.component" :tool-call="result.toolCall" />
+					</div>
 					<template v-for="tc in group.toolCalls" :key="`wait-${tc.toolCallId}`">
 						<N8nText
 							v-if="externalWaitPlatform(tc)"
@@ -593,14 +661,22 @@ watch(
 			>
 				<div :class="$style.content">
 					<AgentChatToolSteps
-						v-if="group.message.toolCalls?.length"
-						:tool-calls="group.message.toolCalls"
+						v-if="getGroupToolCalls(group.id).steps.length"
+						:tool-calls="getGroupToolCalls(group.id).steps"
 						:project-id="projectId"
 						:can-fix-with-assistant="canSendToAssistant"
 						:dismissed-tool-call-ids="dismissedFixToolCallIds"
 						:execution-id="group.message.executionId"
 						@fix-with-assistant="onFixWithAssistant(group, $event)"
 					/>
+					<div
+						v-for="result in getGroupToolCalls(group.id).hostResults"
+						:key="`result-${result.toolCall.toolCallId}`"
+						:class="$style.toolResult"
+						data-testid="agent-chat-host-tool-result"
+					>
+						<component :is="result.renderer.component" :tool-call="result.toolCall" />
+					</div>
 					<template v-for="tc in group.message.toolCalls ?? []" :key="`wait-${tc.toolCallId}`">
 						<N8nText
 							v-if="externalWaitPlatform(tc)"
@@ -847,6 +923,12 @@ watch(
 	margin-bottom: var(--spacing--2xs);
 }
 
+/* A host component that replaces the default step of a finished tool call. */
+.toolResult {
+	margin-top: var(--spacing--2xs);
+	margin-bottom: var(--spacing--2xs);
+}
+
 /* Stretches past the right-aligned user bubble it follows, and stacks the
    hand-off button under the note instead of squeezing it in beside the text.
    `stretch` gives the text row the full width the dismiss button needs to sit
diff --git a/packages/frontend/editor-ui/src/features/agents/utils/agent-plan.ts b/packages/frontend/editor-ui/src/features/agents/utils/agent-plan.ts
index 66589a3afc2..cd14305347a 100644
--- a/packages/frontend/editor-ui/src/features/agents/utils/agent-plan.ts
+++ b/packages/frontend/editor-ui/src/features/agents/utils/agent-plan.ts
@@ -3,6 +3,7 @@ import isEqual from 'lodash/isEqual';
 import omit from 'lodash/omit';
 import {
 	buildDisplayGroups,
+	DISPLAY_GROUP_KIND,
 	type DisplayGroup,
 } from '@/features/ai/shared/agentsChat/displayGroups';
 import type { ChatMessage, ToolCall } from '@/features/ai/shared/agentsChat/types';
@@ -147,8 +148,8 @@ export function buildAgentPlanDisplayGroups(messages: ChatMessage[]): DisplayGro
 	}
 
 	return buildDisplayGroups(messages).flatMap((group): DisplayGroup[] => {
-		if (group.kind === 'backgroundJobSignal') return [group];
-		if (group.kind === 'message') {
+		if (group.kind === DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL) return [group];
+		if (group.kind === DISPLAY_GROUP_KIND.MESSAGE) {
 			return [
 				{
 					...group,
diff --git a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/fixtures/testInteractionExtension.ts b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/fixtures/testInteractionExtension.ts
index 8e44e0bf6f8..b24ea34f597 100644
--- a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/fixtures/testInteractionExtension.ts
+++ b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/fixtures/testInteractionExtension.ts
@@ -56,3 +56,29 @@ export const testInteractionExtension: AgentsChatInteractionExtension<TestCardIn
 export const testInteractionExtensions: readonly AgentsChatInteractionExtension[] = [
 	testInteractionExtension,
 ];
+
+/** Test-only tool whose finished result the host renders. */
+export const TEST_RESULT_TOOL_NAME = 'save_note';
+
+export const TEST_RESULT_EXTENSION_KEY = 'test_result';
+
+export const TestToolResult = defineComponent({
+	name: 'TestToolResult',
+	props: {
+		toolCall: { type: Object as PropType<ToolCall>, required: true },
+	},
+	setup(props) {
+		return () =>
+			h('div', { 'data-testid': 'test-tool-result' }, [
+				h('span', props.toolCall.toolCallId),
+				h('pre', JSON.stringify(props.toolCall.output)),
+			]);
+	},
+});
+
+/** A host extension that only renders tool results. It has no card fields. */
+export const testToolResultExtension: AgentsChatInteractionExtension = {
+	key: TEST_RESULT_EXTENSION_KEY,
+	matchToolResult: (toolCall) => toolCall.tool === TEST_RESULT_TOOL_NAME,
+	resultComponent: TestToolResult,
+};
diff --git a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/toolResultRenderers.test.ts b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/toolResultRenderers.test.ts
new file mode 100644
index 00000000000..9055621f328
--- /dev/null
+++ b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/__tests__/toolResultRenderers.test.ts
@@ -0,0 +1,92 @@
+import { describe, expect, it } from 'vitest';
+
+import { TOOL_CALL_STATE } from '../constants';
+import {
+	findToolResultRenderer,
+	type AgentsChatInteractionExtension,
+} from '../interactionRegistry';
+import type { ToolCall } from '../types';
+import {
+	TEST_RESULT_EXTENSION_KEY,
+	TEST_RESULT_TOOL_NAME,
+	TestToolResult,
+	testInteractionExtension,
+	testToolResultExtension,
+} from './fixtures/testInteractionExtension';
+
+const finishedCall: ToolCall = {
+	tool: TEST_RESULT_TOOL_NAME,
+	toolCallId: 'tc-1',
+	state: TOOL_CALL_STATE.DONE,
+	input: { text: 'Remember this' },
+	output: { saved: true },
+};
+
+describe('findToolResultRenderer', () => {
+	it('returns the host renderer of a result-only extension for a finished call', () => {
+		expect(findToolResultRenderer(finishedCall, [testToolResultExtension])).toEqual({
+			key: TEST_RESULT_EXTENSION_KEY,
+			component: TestToolResult,
+		});
+	});
+
+	it('returns undefined without extensions', () => {
+		expect(findToolResultRenderer(finishedCall, [])).toBeUndefined();
+	});
+
+	it('returns undefined when no extension matches the call', () => {
+		expect(
+			findToolResultRenderer({ ...finishedCall, tool: 'other_tool' }, [testToolResultExtension]),
+		).toBeUndefined();
+	});
+
+	it('ignores extensions that only provide cards', () => {
+		expect(findToolResultRenderer(finishedCall, [testInteractionExtension])).toBeUndefined();
+	});
+
+	it('ignores an extension that matches but has no result component', () => {
+		const extension: AgentsChatInteractionExtension = {
+			...testToolResultExtension,
+			resultComponent: undefined,
+		};
+
+		expect(findToolResultRenderer(finishedCall, [extension])).toBeUndefined();
+	});
+
+	it.each([
+		TOOL_CALL_STATE.PENDING,
+		TOOL_CALL_STATE.RUNNING,
+		TOOL_CALL_STATE.SUSPENDED,
+		TOOL_CALL_STATE.ERROR,
+	])('keeps the default step for a call in state %s', (state) => {
+		expect(
+			findToolResultRenderer({ ...finishedCall, state }, [testToolResultExtension]),
+		).toBeUndefined();
+	});
+
+	it.each([
+		['the cancelled state', { state: TOOL_CALL_STATE.CANCELLED }],
+		['the canceled flag', { canceled: true }],
+	])('keeps the default step for a call canceled with %s', (_, canceled) => {
+		expect(
+			findToolResultRenderer({ ...finishedCall, ...canceled }, [testToolResultExtension]),
+		).toBeUndefined();
+	});
+
+	it('keeps the default step for a finished call without output', () => {
+		expect(
+			findToolResultRenderer({ ...finishedCall, output: undefined }, [testToolResultExtension]),
+		).toBeUndefined();
+	});
+
+	it('uses the first extension that matches', () => {
+		const second: AgentsChatInteractionExtension = {
+			...testToolResultExtension,
+			key: 'second',
+		};
+
+		expect(findToolResultRenderer(finishedCall, [testToolResultExtension, second])?.key).toBe(
+			TEST_RESULT_EXTENSION_KEY,
+		);
+	});
+});
diff --git a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/displayGroups.ts b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/displayGroups.ts
index 12eb6eea34a..d8d0f66ae19 100644
--- a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/displayGroups.ts
+++ b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/displayGroups.ts
@@ -5,6 +5,16 @@ import { getMessageInteractives } from './messageMappers';
 import { getMessageThinkingSegments } from './thinking';
 import type { AgentsChatMessage, InteractivePayload, ThinkingSegment, ToolCall } from './types';
 
+/** Values of the `kind` tag that tells the `DisplayGroup` variants apart. */
+export const DISPLAY_GROUP_KIND = {
+	/** A notice about background jobs of the agent that came to an end. */
+	BACKGROUND_JOB_SIGNAL: 'backgroundJobSignal',
+	/** One user or assistant message that the list does not fold. */
+	MESSAGE: 'message',
+	/** Consecutive tool-only assistant messages folded into one block. */
+	TOOL_RUN: 'toolRun',
+} as const;
+
 /**
  * Presentation group for the message list. The builder persists one assistant
  * message per tool-use turn, so a single conversation fragments into many robot
@@ -19,18 +29,18 @@ import type { AgentsChatMessage, InteractivePayload, ThinkingSegment, ToolCall }
  */
 export type DisplayGroup =
 	| {
-			kind: 'backgroundJobSignal';
+			kind: typeof DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL;
 			id: string;
 			signal: AgentBackgroundJobSignal;
 	  }
 	| {
-			kind: 'message';
+			kind: typeof DISPLAY_GROUP_KIND.MESSAGE;
 			id: string;
 			message: AgentsChatMessage;
 			thinkingSegments: ThinkingSegment[];
 	  }
 	| {
-			kind: 'toolRun';
+			kind: typeof DISPLAY_GROUP_KIND.TOOL_RUN;
 			id: string;
 			thinkingSegments: ThinkingSegment[];
 			active: boolean;
@@ -58,22 +68,26 @@ export type DisplayGroup =
 			executionId?: string;
 	  };
 
-export type TurnDisplayGroup = Exclude<DisplayGroup, { kind: 'backgroundJobSignal' }>;
+export type TurnDisplayGroup = Exclude<
+	DisplayGroup,
+	{ kind: typeof DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL }
+>;
 
 export function isGroupable(message: AgentsChatMessage): boolean {
 	return message.role === 'assistant' && !!message.toolCalls?.length && !message.content.trim();
 }
 
-type ToolRunGroup = Extract<DisplayGroup, { kind: 'toolRun' }>;
+type ToolRunGroup = Extract<DisplayGroup, { kind: typeof DISPLAY_GROUP_KIND.TOOL_RUN }>;
 
 export function isAssistantGroup(group: DisplayGroup): group is TurnDisplayGroup {
 	return (
-		group.kind === 'toolRun' || (group.kind === 'message' && group.message.role === 'assistant')
+		group.kind === DISPLAY_GROUP_KIND.TOOL_RUN ||
+		(group.kind === DISPLAY_GROUP_KIND.MESSAGE && group.message.role === 'assistant')
 	);
 }
 
 function executionIdForGroup(group: TurnDisplayGroup): string | undefined {
-	return group.kind === 'toolRun' ? group.executionId : group.message.executionId;
+	return group.kind === DISPLAY_GROUP_KIND.TOOL_RUN ? group.executionId : group.message.executionId;
 }
 
 /** Keep one reasoning block at the tail of each assistant run, below its final output. */
@@ -208,7 +222,7 @@ export function buildDisplayGroups(messages: AgentsChatMessage[]): DisplayGroup[
 		if (message.role === 'assistant' && message.backgroundJobSignal) {
 			// Keep the signal key stable when the same turn gains text or tool calls.
 			groups.push({
-				kind: 'backgroundJobSignal',
+				kind: DISPLAY_GROUP_KIND.BACKGROUND_JOB_SIGNAL,
 				id: `${message.executionId ?? message.id}:background-job-signal`,
 				signal: message.backgroundJobSignal,
 			});
@@ -223,7 +237,7 @@ export function buildDisplayGroups(messages: AgentsChatMessage[]): DisplayGroup[
 		}
 		if (isGroupable(message)) {
 			const last = groups[groups.length - 1];
-			if (last?.kind === 'toolRun' && canAppendToToolRun(last, message)) {
+			if (last?.kind === DISPLAY_GROUP_KIND.TOOL_RUN && canAppendToToolRun(last, message)) {
 				last.toolCalls = appendToolCalls(last.toolCalls, message.toolCalls ?? []);
 				last.thinkingSegments.push(...getMessageThinkingSegments(message));
 				last.active ||= message.status === 'streaming';
@@ -237,7 +251,7 @@ export function buildDisplayGroups(messages: AgentsChatMessage[]): DisplayGroup[
 				continue;
 			}
 			groups.push({
-				kind: 'toolRun',
+				kind: DISPLAY_GROUP_KIND.TOOL_RUN,
 				id: message.id,
 				thinkingSegments: getMessageThinkingSegments(message),
 				active: message.status === 'streaming',
@@ -252,7 +266,7 @@ export function buildDisplayGroups(messages: AgentsChatMessage[]): DisplayGroup[
 
 		if (message.role === 'assistant') {
 			const last = groups[groups.length - 1];
-			if (last?.kind === 'toolRun' && canAppendToToolRun(last, message)) {
+			if (last?.kind === DISPLAY_GROUP_KIND.TOOL_RUN && canAppendToToolRun(last, message)) {
 				last.finalMessage = message;
 				last.executionId ??= message.executionId;
 				last.thinkingSegments.push(...getMessageThinkingSegments(message));
@@ -271,7 +285,7 @@ export function buildDisplayGroups(messages: AgentsChatMessage[]): DisplayGroup[
 		}
 
 		groups.push({
-			kind: 'message',
+			kind: DISPLAY_GROUP_KIND.MESSAGE,
 			id: message.id,
 			message,
 			thinkingSegments: message.role === 'assistant' ? getMessageThinkingSegments(message) : [],
diff --git a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/interactionRegistry.ts b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/interactionRegistry.ts
index a30cb57b301..2c2453e5bbe 100644
--- a/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/interactionRegistry.ts
+++ b/packages/frontend/editor-ui/src/features/ai/shared/agentsChat/interactionRegistry.ts
@@ -1,5 +1,6 @@
 import type { Component, ComputedRef, InjectionKey } from 'vue';
 
+import { TOOL_CALL_STATE } from './constants';
 import type { AgentsChatInteraction, ToolCall } from './types';
 
 export interface AgentsChatInteractionRenderer {
@@ -17,6 +18,11 @@ export interface AgentsChatInteractionRenderer {
  * The card fields (`parse` and `component`) are optional, so a host can add
  * other parts without a card. The chat maps a card only with `parse`, and
  * renders it only with `component`. Set both for a card.
+ *
+ * An extension can also render the result of a finished tool call
+ * (`matchToolResult` and `resultComponent`). The chat then shows the host
+ * component in place of the default tool step. An extension that only renders
+ * results needs no card fields.
  */
 export interface AgentsChatInteractionExtension<TInput = unknown> {
 	/** Unique key. The payload stores it as `extensionKey`. */
@@ -37,6 +43,23 @@ export interface AgentsChatInteractionExtension<TInput = unknown> {
 	 * default: the chat cancels the card and steers the run with the text.
 	 */
 	composerResumeData?(input: TInput, text: string): unknown;
+	/**
+	 * True when the host renders the result of this tool call. The chat asks
+	 * only for calls that finished with an output, without an error or a cancel.
+	 */
+	matchToolResult?(toolCall: ToolCall): boolean;
+	/**
+	 * Renders a matched tool result. It gets the finished call as the `toolCall`
+	 * prop. When this extension also renders a card for the tool, `output` is
+	 * the resume data until the tool result arrives.
+	 */
+	resultComponent?: Component;
+}
+
+/** A host component that renders the result of one finished tool call. */
+export interface AgentsChatToolResultRenderer {
+	key: string;
+	component: Component;
 }
 
 /** The extensions of the chat panel, for the interactive cards that it renders. */
@@ -50,3 +73,33 @@ export function findInteractionRenderer(
 ): AgentsChatInteractionRenderer | undefined {
 	return renderers.find((renderer) => renderer.matches(payload));
 }
+
+/**
+ * `tool-execution-end` and the stream finalizer set `DONE` before the output
+ * arrives, so a call without output is not finished yet.
+ */
+function isFinishedToolCall(toolCall: ToolCall): boolean {
+	return (
+		toolCall.state === TOOL_CALL_STATE.DONE &&
+		toolCall.canceled !== true &&
+		toolCall.output !== undefined
+	);
+}
+
+/**
+ * The first host extension that renders the result of `toolCall`, or
+ * `undefined` when the chat shows the default tool step. Calls that run, wait
+ * for the user, fail, were canceled or have no output yet always use the
+ * default tool step.
+ */
+export function findToolResultRenderer(
+	toolCall: ToolCall,
+	extensions: readonly AgentsChatInteractionExtension[],
+): AgentsChatToolResultRenderer | undefined {
+	if (!isFinishedToolCall(toolCall)) return undefined;
+	for (const extension of extensions) {
+		if (!extension.resultComponent || !extension.matchToolResult?.(toolCall)) continue;
+		return { key: extension.key, component: extension.resultComponent };
+	}
+	return undefined;
+}