ToolLoop

The model/tool loop as a graph - the Stage 0 proof of runtime-owned tool results and resumable approval ((#1269)):

input -> model --fan-out, one task per call--> call-tool --(dynamic join "tool-batch")--> collect -> model
                                                  \--suspend--> approval --/

• Each call is its own task: policy first, then the tool. A policy RequireApproval and a tool's NeedsApproval both suspend the call with an ApprovalRequest and resume at the one approval node, whose continuation fills that call's slot in the batch barrier.
• The loop, not the tool, records exactly one ToolResult per call - for success, failure, denial, rejection and unknown tools alike; the results key refuses a second one.
• collect runs only when the barrier releases, checks every call of the batch has exactly one result, and appends the ToolMessages in call order. The model never sees a partial batch.
• The model node re-checks the history with Message.validateConversation before every call.