feat: VersionGuard — newer-major sidecars are read-only with one warning (F5 SLICE-2, INV-16/PUC-4, #14)

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

src/attributionController.ts

@@ -16,6 +16,7 @@ import { buildFingerprint, resolve, type OffsetRange } from "./anchorer";
 import { gitUserEmail } from "./identity";
 import { applyChange, coalesce, type LiveSpan } from "./attributionTracker";
 import { minimizeReplace, PendingEditRegistry } from "./pendingEdits";
+import type { VersionGuard } from "./versionGuard";
 
 /** Test-facing snapshot of live attribution state for a document. */
 export interface RenderedSpan {
@@ -62,7 +63,11 @@ export class AttributionController implements vscode.Disposable {
   private readonly output = vscode.window.createOutputChannel("Cowriting Attribution");
   private visible = true;
 
-  constructor(private readonly store: CoauthorStore, private readonly rootDir: string) {
+  constructor(
+    private readonly store: CoauthorStore,
+    private readonly rootDir: string,
+    private readonly guard: VersionGuard,
+  ) {
     this.disposables.push(this.agentType, this.humanType, this.statusItem, this.output);
     this.disposables.push(
       vscode.commands.registerCommand("cowriting.toggleAttribution", () => this.toggle()),
@@ -277,6 +282,7 @@ export class AttributionController implements vscode.Disposable {
 
   private onDidSave(document: vscode.TextDocument): void {
     if (!this.isTracked(document)) return;
+    if (this.guard.isReadOnly(this.docPathOf(document.uri))) return;
     const docPath = this.docPathOf(document.uri);
     const s = this.docs.get(docPath);
     // Allow save when hadAttributions is true even if spans/orphans are now empty: