feat(f7): additive onDidChangeBaseline event on DiffViewController (#21)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/diffViewController.ts

@@ -26,6 +26,11 @@ export class DiffViewController implements vscode.Disposable {
   /** Source of truth for the content provider, keyed by `document.uri.toString()`. */
   private readonly baselines = new Map<string, Baseline>();
   private readonly onDidChangeEmitter = new vscode.EventEmitter<vscode.Uri>();
+  /** F7 (additive): fires on every baseline capture (open / advance / pin) so
+   *  the track-changes preview refreshes without polling. Mirrors the internal
+   *  content-provider change signal but carries the real document URI. */
+  private readonly onDidChangeBaselineEmitter = new vscode.EventEmitter<{ uri: string }>();
+  readonly onDidChangeBaseline = this.onDidChangeBaselineEmitter.event;
   private storageWarned = false;
 
   constructor(private readonly store: BaselineStore | null) {
@@ -38,6 +43,7 @@ export class DiffViewController implements vscode.Disposable {
     };
     this.disposables.push(
       this.onDidChangeEmitter,
+      this.onDidChangeBaselineEmitter,
       vscode.workspace.registerTextDocumentContentProvider(BASELINE_SCHEME, provider),
       vscode.commands.registerCommand("cowriting.toggleDiffView", () =>
         this.toggle(vscode.window.activeTextEditor),
@@ -123,6 +129,7 @@ export class DiffViewController implements vscode.Disposable {
     }
     // An open diff re-requests the left side when its baseline URI changes.
     this.onDidChangeEmitter.fire(this.baselineUri(document));
+    this.onDidChangeBaselineEmitter.fire({ uri: key });
   }
 
   private warnStorageOnce(): void {