fix: harden generated agent platform access

agent_builder/skills/a2apack-agent-authoring/SKILL.md

@@ -21,6 +21,12 @@ Use `A2AAgent` class attributes for runtime and marketplace behavior:
 - `wants_cp_jwt=True` is only for trusted platform agents. It forwards the
   caller's control-plane token.
 
+For generated/user-owned agents that call an LLM, default to
+`LLMProvisioning.CALLER_PROVIDED` with `Pricing(..., caller_pays_llm=True, ...)`.
+Use `LLMProvisioning.PLATFORM` only when the user explicitly wants
+platform-paid LLM usage. In either mode, read `ctx.llm`; never read
+`A2A_LITELLM_KEY`, provider keys, or platform secrets directly.
+
 Keep each `@skill` method `async`, put `RunContext[...]` immediately after
 `self`, and annotate every public argument. Do not use `*args` or `**kwargs`;
 they are rejected and would not publish a useful schema.