feat: AI nodes usability fixes + Summarization Chain V2 (#7949)

Fixes:
- Refactor connection snapping when dragging and enable it also for
non-main connection types
- Fix propagation of errors from sub-nodes
- Fix chat scrolling when sending/receiving messages
- Prevent empty chat messages
- Fix sub-node selected styles
- Fix output names text overflow

Usability improvements:
- Auto-add manual chat trigger for agents & chain nodes
- Various labels and description updates
- Make the output parser input optional for Basic LLM Chain
- Summarization Chain V2 with a simplified document loader & text
chunking mode

#### How to test the change:
Example workflow showcasing different operation mode of the new
summarization chain:

[Summarization_V2.json](https://github.com/n8n-io/n8n/files/13599901/Summarization_V2.json)


## Issues fixed
Include links to Github issue or Community forum post or **Linear
ticket**:
> Important in order to close automatically and provide context to
reviewers
-
https://www.notion.so/n8n/David-Langchain-Posthog-notes-7a9294938420403095f4508f1a21d31d
- https://linear.app/n8n/issue/N8N-7070/ux-fixes-batch
- https://linear.app/n8n/issue/N8N-7071/ai-sub-node-bugs


## Review / Merge checklist
- [x] PR title and summary are descriptive. **Remember, the title
automatically goes into the changelog. Use `(no-changelog)` otherwise.**
([conventions](https://github.com/n8n-io/n8n/blob/master/.github/pull_request_title_conventions.md))
- [x] [Docs updated](https://github.com/n8n-io/n8n-docs) or follow-up
ticket created.
- [ ] Tests included.
> A bug is not considered fixed, unless a test is added to prevent it
from happening again. A feature is not complete without tests.
  >
> *(internal)* You can use Slack commands to trigger [e2e
tests](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#a39f9e5ba64a48b58a71d81c837e8227)
or [deploy test
instance](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#f6a177d32bde4b57ae2da0b8e454bfce)
or [deploy early access version on
Cloud](https://www.notion.so/n8n/Cloudbot-3dbe779836004972b7057bc989526998?pvs=4#fef2d36ab02247e1a0f65a74f6fb534e).

---------

Signed-off-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Elias Meire <elias@meire.dev>

packages/@n8n/nodes-langchain/utils/N8nBinaryLoader.ts

@@ -1,5 +1,5 @@
 import type { IExecuteFunctions, INodeExecutionData } from 'n8n-workflow';
-import { NodeOperationError, NodeConnectionType, BINARY_ENCODING } from 'n8n-workflow';
+import { NodeOperationError, BINARY_ENCODING } from 'n8n-workflow';
 
 import type { TextSplitter } from 'langchain/text_splitter';
 import type { Document } from 'langchain/document';
@@ -30,9 +30,15 @@ export class N8nBinaryLoader {
 
 	private optionsPrefix: string;
 
-	constructor(context: IExecuteFunctions, optionsPrefix = '') {
+	private binaryDataKey: string;
+
+	private textSplitter?: TextSplitter;
+
+	constructor(context: IExecuteFunctions, optionsPrefix = '', binaryDataKey = '', textSplitter?: TextSplitter) {
 		this.context = context;
+		this.textSplitter = textSplitter;
 		this.optionsPrefix = optionsPrefix;
+		this.binaryDataKey = binaryDataKey;
 	}
 
 	async processAll(items?: INodeExecutionData[]): Promise<Document[]> {
@@ -53,17 +59,15 @@ export class N8nBinaryLoader {
 		const selectedLoader: keyof typeof SUPPORTED_MIME_TYPES = this.context.getNodeParameter(
 			'loader',
 			itemIndex,
+			'auto',
 		) as keyof typeof SUPPORTED_MIME_TYPES;
 
-		const binaryDataKey = this.context.getNodeParameter('binaryDataKey', itemIndex) as string;
 		const docs: Document[] = [];
 		const metadata = getMetadataFiltersValues(this.context, itemIndex);
 
 		if (!item) return [];
 
-		// TODO: Should we support traversing the object to find the binary data?
-		const binaryData = this.context.helpers.assertBinaryData(itemIndex, binaryDataKey);
-
+		const binaryData = this.context.helpers.assertBinaryData(itemIndex, this.binaryDataKey)
 		const { mimeType } = binaryData;
 
 		// Check if loader matches the mime-type of the data
@@ -174,12 +178,8 @@ export class N8nBinaryLoader {
 				loader = new TextLoader(filePathOrBlob);
 		}
 
-		const textSplitter = (await this.context.getInputConnectionData(
-			NodeConnectionType.AiTextSplitter,
-			0,
-		)) as TextSplitter | undefined;
 
-		const loadedDoc = textSplitter ? await loader.loadAndSplit(textSplitter) : await loader.load();
+		const loadedDoc = this.textSplitter ? await loader.loadAndSplit(this.textSplitter) : await loader.load();
 
 		docs.push(...loadedDoc);
 

packages/@n8n/nodes-langchain/utils/N8nJsonLoader.ts

@@ -1,11 +1,10 @@
 import {
 	type IExecuteFunctions,
 	type INodeExecutionData,
-	NodeConnectionType,
 	NodeOperationError,
 } from 'n8n-workflow';
 
-import type { CharacterTextSplitter } from 'langchain/text_splitter';
+import type { TextSplitter } from 'langchain/text_splitter';
 import type { Document } from 'langchain/document';
 import { JSONLoader } from 'langchain/document_loaders/fs/json';
 import { TextLoader } from 'langchain/document_loaders/fs/text';
@@ -16,8 +15,11 @@ export class N8nJsonLoader {
 
 	private optionsPrefix: string;
 
-	constructor(context: IExecuteFunctions, optionsPrefix = '') {
+	private textSplitter?: TextSplitter;
+
+	constructor(context: IExecuteFunctions, optionsPrefix = '', textSplitter?: TextSplitter) {
 		this.context = context;
+		this.textSplitter = textSplitter;
 		this.optionsPrefix = optionsPrefix;
 	}
 
@@ -46,11 +48,6 @@ export class N8nJsonLoader {
 			'',
 		) as string;
 		const pointersArray = pointers.split(',').map((pointer) => pointer.trim());
-
-		const textSplitter = (await this.context.getInputConnectionData(
-			NodeConnectionType.AiTextSplitter,
-			0,
-		)) as CharacterTextSplitter | undefined;
 		const metadata = getMetadataFiltersValues(this.context, itemIndex) ?? [];
 
 		if (!item) return [];
@@ -81,8 +78,8 @@ export class N8nJsonLoader {
 			throw new NodeOperationError(this.context.getNode(), 'Document loader is not initialized');
 		}
 
-		const docs = textSplitter
-			? await documentLoader.loadAndSplit(textSplitter)
+		const docs = this.textSplitter
+			? await documentLoader.loadAndSplit(this.textSplitter)
 			: await documentLoader.load();
 
 		if (metadata) {

packages/@n8n/nodes-langchain/utils/logWrapper.ts

@@ -48,6 +48,8 @@ export async function callMethodAsync<T>(
 	try {
 		return await parameters.method.call(this, ...parameters.arguments);
 	} catch (e) {
+		// Propagate errors from sub-nodes
+		if (e.functionality === 'configuration-node') throw e;
 		const connectedNode = parameters.executeFunctions.getNode();
 
 		const error = new NodeOperationError(connectedNode, e, {
@@ -89,6 +91,8 @@ export function callMethodSync<T>(
 	try {
 		return parameters.method.call(this, ...parameters.arguments);
 	} catch (e) {
+		// Propagate errors from sub-nodes
+		if (e.functionality === 'configuration-node') throw e;
 		const connectedNode = parameters.executeFunctions.getNode();
 		const error = new NodeOperationError(connectedNode, e);
 		parameters.executeFunctions.addOutputData(