fix(phase-lifecycle): fast-path replaceInCurrentMilestone only when pattern matches after

The previous guard `if (after.trim().length > 0)` incorrectly triggered
when `after` contained only footer text (e.g. `---\n*Last updated*`).
In that case `after.replace(pattern, replacement)` is a no-op and the
function returned unchanged content instead of falling through to the
slow path that searches inside the last `<details>` block.

Fix: capture the replaced string first, then only take the fast path
when the replacement actually changed `after`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sdk/src/query/phase-lifecycle.ts

@@ -111,8 +111,9 @@ export function replaceInCurrentMilestone(
 
   // Fast path: the current milestone is not inside a <details> block — the
   // pattern lives in the plain text after the last </details>.
-  if (after.trim().length > 0) {
-    return before + after.replace(pattern, replacement);
+  const replacedAfter = after.replace(pattern, replacement);
+  if (replacedAfter !== after) {
+    return before + replacedAfter;
   }
 
   // Slow path: the active milestone is inside the last <details> block.