docs(runtime): the two guards on the park-time binding are not redundant

Recording a reconciliation result that existed only in a review thread, and
correcting it in the process — measuring the claim changed it.

The claim under review was that the `?? ''` fallback in `recordExpiredWait` is
unreachable by two independent guards, either sufficient alone: the caller's
generation gate (a missing waiter fails `undefined === number`) and the
record-before-release ordering. That is not what the code does.

Measured, by removing each in turn:

  - ordering removed, generation gate kept: the gate does NOT carry it. With the
    waiter already deleted, the gate is false on every expiry, so nothing is ever
    recorded — five failures, and the door is shut by breaking the mechanism rather
    than by refusing ''.
  - generation gate removed, ordering kept: 736 files green, one failure, and it is
    `does not let a wait armed on the previous connection decide the new one` in
    host-mirror-handle-gap-resume.test.ts — a different property entirely.

So the ordering alone makes `''` unreachable, and the generation gate is not a second
guard on it at all: it pins reconnect-void. Both are load-bearing, for different
reasons, which is a stronger argument against removing either than redundancy would
have been — redundancy invites deleting one.

Worth writing in the file because the two sit three lines apart and read as belt and
braces on the same thing. The `''` comment next to them already exists because an
unexplained guard on an unreachable value gets deleted as dead code in a year; a guard
that looks redundant is deleted sooner.

No behaviour change. One comment, corrected against measurement rather than against the
thread it came from.

src/renderer/src/lib/host-mirror-handle-gap-wait.ts

@@ -159,6 +159,11 @@ function recordExpiredWait(environmentId: string, key: string): void {
   // wait just ran out. Re-reading here would attribute it to whatever holds the id NOW, handing a
   // pane that replaced it mid-wait a verdict it never served. The caller must therefore record
   // BEFORE `releaseWaiter` deletes the entry; the union suite pins that ordering.
+  // The `?? ''` is unreachable solely because of the record-before-release ordering above it. The
+  // caller's generation gate LOOKS like a second guard on it and is not: drop the ordering and that
+  // gate stops recording anything at all rather than admitting ''. It pins a different property
+  // (reconnect-void, host-mirror-handle-gap-resume.test.ts). Both are load-bearing, for different
+  // reasons — do not collapse them as redundant.
   expiredGenerationByPane.set(key, {
     generation,
     paneBinding: waitersByPane.get(key)?.paneBinding ?? ''