Refactor agent architecture and add session storage

Major architectural improvements:
- Renamed AgentSession → Agent (state/ → agent/)
- Removed id field from AgentState
- Fixed transport abstraction to pass messages directly instead of using callbacks
- Eliminated circular dependencies in transport creation

Transport changes:
- Changed signature: run(messages, userMessage, config, signal)
- Removed getMessages callback from ProviderTransport and AppTransport
- Transports now filter attachments internally

Session storage:
- Added SessionRepository with IndexedDB backend
- Auto-save sessions after first exchange
- Auto-generate titles from first user message
- Session list dialog with search and delete
- Persistent storage permission dialog
- Browser extension now auto-loads last session

UI improvements:
- ChatPanel creates single AgentInterface instance in setAgent()
- Added drag & drop file upload to MessageEditor
- Fixed artifacts panel auto-opening on session load
- Added "Drop files here" i18n strings
- Changed "Continue Without Saving" → "Continue Anyway"

Web example:
- Complete rewrite of main.ts with clean architecture
- Added check script to package.json
- Session management with URL state
- Editable session titles

Browser extension:
- Added full session storage support
- History and new session buttons
- Auto-load most recent session on open
- Session titles in header

packages/web-ui/src/components/AgentInterface.ts

@@ -7,7 +7,7 @@ import type { MessageEditor } from "./MessageEditor.js";
 import "./MessageEditor.js";
 import "./MessageList.js";
 import "./Messages.js"; // Import for side effects to register the custom elements
-import type { AgentSession, AgentSessionEvent } from "../state/agent-session.js";
+import type { Agent, AgentEvent } from "../agent/agent.js";
 import { getAppStorage } from "../storage/app-storage.js";
 import "./StreamingMessageContainer.js";
 import type { Attachment } from "../utils/attachment-utils.js";
@@ -18,7 +18,7 @@ import type { StreamingMessageContainer } from "./StreamingMessageContainer.js";
 @customElement("agent-interface")
 export class AgentInterface extends LitElement {
 	// Optional external session: when provided, this component becomes a view over the session
-	@property({ attribute: false }) session?: AgentSession;
+	@property({ attribute: false }) session?: Agent;
 	@property() enableAttachments = true;
 	@property() enableModelSelector = true;
 	@property() enableThinkingSelector = true;
@@ -52,6 +52,15 @@ export class AgentInterface extends LitElement {
 		return this;
 	}
 
+	override willUpdate(changedProperties: Map<string, any>) {
+		super.willUpdate(changedProperties);
+
+		// Re-subscribe when session property changes
+		if (changedProperties.has("session")) {
+			this.setupSessionSubscription();
+		}
+	}
+
 	override async connectedCallback() {
 		super.connectedCallback();
 
@@ -84,11 +93,6 @@ export class AgentInterface extends LitElement {
 
 		// Subscribe to external session if provided
 		this.setupSessionSubscription();
-
-		// Attach debug listener if session provided
-		if (this.session) {
-			this.session = this.session; // explicitly set to trigger subscription
-		}
 	}
 
 	override disconnectedCallback() {
@@ -116,7 +120,7 @@ export class AgentInterface extends LitElement {
 			this._unsubscribeSession = undefined;
 		}
 		if (!this.session) return;
-		this._unsubscribeSession = this.session.subscribe(async (ev: AgentSessionEvent) => {
+		this._unsubscribeSession = this.session.subscribe(async (ev: AgentEvent) => {
 			if (ev.type === "state-update") {
 				if (this._streamingContainer) {
 					this._streamingContainer.isStreaming = ev.state.isStreaming;