F3 SLICE-3 host fixes: disk-compare sync detection + self-minimized seam edits (INV-9) (#6)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/pendingEdits.ts

@@ -7,6 +7,27 @@
  */
 import type { Provenance } from "./model";
 
+/**
+ * Greedily trim the common prefix then common suffix between the replaced
+ * text and its replacement (non-overlapping), mirroring the host's own
+ * WorkspaceEdit diff-minimization so a registered seam edit matches the
+ * change event VS Code actually delivers (INV-9).
+ */
+export function minimizeReplace(
+  oldText: string,
+  newText: string,
+): { prefix: number; suffix: number } {
+  const max = Math.min(oldText.length, newText.length);
+  let prefix = 0;
+  while (prefix < max && oldText[prefix] === newText[prefix]) prefix++;
+  let suffix = 0;
+  while (
+    suffix < max - prefix &&
+    oldText[oldText.length - 1 - suffix] === newText[newText.length - 1 - suffix]
+  ) suffix++;
+  return { prefix, suffix };
+}
+
 export interface PendingEdit {
   docPath: string;
   /** half-open [start, end) offsets of the replaced range. */
@@ -15,6 +36,14 @@ export interface PendingEdit {
   newText: string;
   provenance: Provenance;
   turnId?: string;
+  /**
+   * The agent's full intended replacement before self-minimization (pre-edit
+   * half-open range + replacement length). The minimized start/end/newText are
+   * transport-only (so the registration matches the host-delivered change);
+   * attribution uses this extent — the agent owns every char it asserted,
+   * including chars the minimized diff left unchanged.
+   */
+  full?: { start: number; end: number; newLength: number };
 }
 
 export class PendingEditRegistry {