fix(#70): INV-5 — reject after an interior tweak restores the retained original (PR #73)

Reject on an optimistically-applied proposal now restores the retained original even after interior tweaks: appliedSpans tracked-range fallback (pure shiftTracked, boundary-straddle distrust, close-clears, rebuild-only resync), honest hard failure with a Discard action, INV-16 read-only guards, rejectAll {reverted,skipped} reporting on all batch surfaces, CodeLens reachability at the tracked span. 312 unit + 94/5 host E2E.

Closes #70.

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

src/anchorer.ts

@@ -101,6 +101,30 @@ export function resolve(docText: string, fp: Fingerprint): OffsetRange | "orphan
   return "orphaned";
 }
 
+/**
+ * #70 (INV-5/INV-11): maintain a TRACKED applied span across an in-session edit.
+ * Unlike `shift`, which clamps every point into a best-effort range, a tracked
+ * span must stay *provably* meaningful — it is a revert target. So:
+ *   - an edit fully OUTSIDE or fully INSIDE the span shifts it (the span is
+ *     still "the applied block, as tweaked");
+ *   - an insertion exactly AT the span start lands BEFORE the span (both ends
+ *     shift right) — matching exact-resolve semantics, where text typed just
+ *     before the applied block is never part of it;
+ *   - any edit STRADDLING a span boundary returns "distrusted": the shifted
+ *     result would be a clamped guess, and stale text is never reverted by
+ *     guess (INV-11).
+ */
+export function shiftTracked(range: OffsetRange, edit: TextEdit): OffsetRange | "distrusted" {
+  const delta = edit.newLength - (edit.end - edit.start);
+  if (edit.start === edit.end && edit.start === range.start) {
+    return { start: range.start + delta, end: range.end + delta };
+  }
+  const outside = edit.end <= range.start || edit.start >= range.end;
+  const inside = edit.start >= range.start && edit.end <= range.end;
+  if (!outside && !inside) return "distrusted";
+  return shift(range, edit);
+}
+
 /** Maintain a live range across an in-session edit (spec §6.4 `shift`). */
 export function shift(range: OffsetRange, edit: TextEdit): OffsetRange {
   const delta = edit.newLength - (edit.end - edit.start);