Let the model choose which ready work item to switch to

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/Architecture-Build-Spec.md

@@ -161,9 +161,12 @@ come back to something. Components throughout this document refer to them.
   item, so boot reconciliation (A3) stays single-item.
 - **The operator can always switch; the agent may switch on its own in one case.**
   When the active work item is waiting on the operator (an open gate, a pending
-  question, or a halt in `AWAIT_INPUT`) and another work item is ready, the agent
-  switches to it, oldest first, and posts a notice naming both items. An alert
-  must not sit for hours behind an unanswered prompt. The agent never switches
+  question, or a halt in `AWAIT_INPUT`) and other work items are ready, the agent
+  switches to one of them and posts a notice naming both items and why it chose
+  that one. The model chooses. This is one of the few judgments it is trusted with
+  outright, because choosing grants nothing: every item still meets its own gates,
+  and a poor choice costs time, not safety. An alert must not sit for hours behind
+  an unanswered prompt. The agent never switches
   away from an item that is working. The item it left stays waiting; switching
   answers nothing on its behalf.
 - **Parking gives up authority.** Parking a work item unmounts any elevated MCP