Can Strands Decider 2B pick which Sume MCP tool to call?

Yes, as the step that chooses a tool name. Strands lists "model routing and tool selection" among the uses of Decider 2B on its launch post, and the model scores answers from a list that you provide. Sume's hosted MCP gives you that list: tools_list returns the tools that the current session can see, and tools_schema returns one tool's contract by name. The decision picks a name. It never replaces the schema read or the spend checks.

Turn tools_list into one choice question

The Hugging Face model card says that options go in as typed questions, for example --choice "question=option1,option2,option3", next to a state that gives the context. The card also warns that questions are read less than documents, so keep the option names short and make them the exact Sume tool ids.

Three steps, three owners

Keep the decision, the validation and the paid step apart. The table shows which Sume call belongs to which step.

TOOLS = ["balance_get", "catalog_list", "generate_image", "tts_create", "music_create"]
PAID = {"generate_image", "tts_create", "music_create"}


def choice_question(question: str, options: list[str]) -> str:
    return f'--choice "{question}={",".join(options)}"'


def accept(choice: str) -> str:
    if choice not in TOOLS:
        raise ValueError(f"not a tool in tools_list: {choice}")
    return choice


print(choice_question("which tool answers the user", TOOLS))
name = accept("tts_create")
print(name, "needs a dry run first" if name in PAID else "is read-only")

Keep the option list live

Under OAuth mcp:read, the paid tools are hidden from the session, so the list that you give the model is already shorter. Build the options from the live tools_list of the session, not from a hardcoded copy, or Decider can choose a tool that the session answers with insufficient_scope.

Also reject any answer that is not in the list. A decision model scores the options that you give it, so the failure to guard against is a stale option list, not an invented tool.