feat(spec): add ToolExecutionContext.userMessageText contract field

Optional, neutral field carrying the latest user message — for a tool to detect
explicit user intent (e.g. a confirm/approval) without re-deriving it from the
transcript. Consumed by cloud's confirm-before-change gate.

Scope reduced after #2325 (ADR-0025) removed framework service-ai: the agent
route that POPULATES this now lives with the AI runtime (cloud-owned), so this
PR adds only the contract field; cloud wires the value when it owns the route.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: os-zhuang

packages/spec/src/contracts/ai-service.ts

@@ -427,6 +427,13 @@ export interface ToolExecutionContext {
     currentObjectName?: string;
     /** View the user is currently viewing, if known. */
     currentViewName?: string;
+    /**
+     * Text of the latest user message (neutral context, like currentObjectName).
+     * Forwarded so a tool can detect intent — e.g. an explicit confirm/approval —
+     * without re-deriving it from the transcript. Consumers own any semantics.
+     * Populated by whichever layer owns the agent route (cloud, post-ADR-0025).
+     */
+    userMessageText?: string;
     /** Distributed-trace id for cross-service correlation. */
     traceId?: string;
     /**