test(voice): pin diagnostics wiring and in-flight crop dedupe; tighten docs

Third review pass on #835. No runtime change.

- Controller test: viewport decisions reach the controller's debug log.
- Policy test: a second request for a snapshot still being captured is
  logged pointer-already-requested and is not captured twice.
- CURRENT-STATE: pointer-not-fresh also covers a missing snapshot,
  already-requested covers an earlier attempt that threw, and the image
  step runs when any tool output of the response was sent.
- Changelog: describe what is recorded rather than a fixed miscount.

changelog.d/835-viewport-escalation-reasons.md

@@ -1,7 +1,7 @@
 - The voice debug log now says why OpenAI Realtime did or did not get a
   viewport screenshot or pointer crop. When an entity-context answer reaches
   the image step, the log records a reason-coded decision and, when an image
-  was due, one outcome under the same id, so a crop that was dropped because
-  the pointer went stale or the camera moved is no longer counted as sent.
-  What is captured, sent and kept is unchanged, and no image data or user text
-  is logged (kvnloo, manjunath22466, #835).
+  was due, one outcome under the same id: sent, or why it was dropped (a stale
+  pointer, a camera move, a newer turn). What is captured, sent and kept is
+  unchanged, and no image data or user text is logged (kvnloo, manjunath22466,
+  #835).