Editor opens in native windows (one per file)

Real BrowserWindow per edited file with its own RPC instance, deduped by
sessionId+path. The same Angular bundle boots an editor-only root via
preload globals. Native close isn't cancellable in electrobun, so the
editor mirrors its draft to bun; traffic-light closes get a native
Save/Discard prompt after the fact, and failed saves park the draft in
the edit-leftovers dir. In-window closes (Cmd+W, Close) use a styled
prompt; the quit guard now also counts unsaved editors.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/bun/rpc-handlers.ts

@@ -1,6 +1,6 @@
 import { BrowserView, Utils } from "electrobun/bun";
-import type { AppRPC } from "../shared/rpc";
-import { effectiveConcurrency, type Result } from "../shared/types";
+import type { AppRPC, EditorOpenContext } from "../shared/rpc";
+import { effectiveConcurrency, type AppSettings, type Result } from "../shared/types";
 import type { PanelContextMenu } from "./context-menu";
 import { readFileText, writeFileText, type EditManager } from "./edits";
 import type { SessionRegistry } from "./fs/registry";
@@ -27,6 +27,8 @@ export interface AppDeps {
 	events: {
 		sessionClosed: (info: { sessionId: string; reason: string }) => void;
 		connectionsChanged: () => void;
+		openEditor: (ctx: EditorOpenContext) => void;
+		settingsChanged: (settings: AppSettings) => void;
 	};
 }
 
@@ -195,6 +197,7 @@ export function createAppRPC({
 					wrap(async () => {
 						await settings.save(next);
 						engine.setConcurrency(effectiveConcurrency(next));
+						events.settingsChanged(next);
 						return {};
 					}),
 
@@ -261,6 +264,64 @@ export function createAppRPC({
 						Utils.moveToTrash(path);
 						return {};
 					}),
+
+				// ---- editor windows ----
+				openEditor: (ctx) =>
+					wrap(async () => {
+						events.openEditor(ctx);
+						return {};
+					}),
+			},
+		},
+	});
+}
+
+export interface EditorRpcHooks {
+	ctx: EditorOpenContext;
+	/** Draft mirror tick: store dirty flag + content on the window record. */
+	onDraft: (state: { dirty: boolean; content: string }) => void;
+	/** editorSave succeeded: clean the record, retitle, refresh main panels. */
+	onSaved: () => void;
+	/** Webview resolved its dirty prompt: close without the native fallback. */
+	onCloseConfirmed: () => void;
+}
+
+/**
+ * RPC for one editor window. Each window MUST get its own instance (binding a
+ * BrowserView steals the rpc's transport), and the hooks close over that
+ * window's record — no ids on the wire.
+ */
+export function createEditorRPC(
+	deps: { registry: SessionRegistry; settings: SettingsStore },
+	hooks: EditorRpcHooks,
+) {
+	return BrowserView.defineRPC<AppRPC>({
+		maxRequestTime: MAX_REQUEST_TIME_MS,
+		handlers: {
+			requests: {
+				readFile: ({ sessionId, path }) =>
+					wrap(async () => ({
+						content: await readFileText(deps.registry.get(sessionId), path),
+					})),
+
+				getSettings: () => wrap(async () => ({ settings: await deps.settings.load() })),
+
+				editorSave: ({ content }) =>
+					wrap(async () => {
+						const { sessionId, path } = hooks.ctx;
+						await writeFileText(deps.registry.get(sessionId), path, content);
+						hooks.onSaved();
+						return {};
+					}),
+
+				editorClose: () =>
+					wrap(async () => {
+						hooks.onCloseConfirmed();
+						return {};
+					}),
+			},
+			messages: {
+				editorState: (state) => hooks.onDraft(state),
 			},
 		},
 	});