[SaladDay]

Claude Code Subagents can now call the Agent's function and HTTP MCP tools, as a local Claude Code run does. MiniMax Code Subagents are admitted with functions too. This builds on #780.

• Calls: a child's function call reaches Core with the child's native_id and turn_id, so it becomes a required action of the root Turn under the child's call_id. The receipt comes from the child's own native tool result.
• Withdrawal: when native aborts a child's pending call, for example on root cancellation, the bridge emits function_call_withdrawn.
• Admission: no declaration rejects function or MCP tools beside multi_agent, and the RejectSubagentTools helper is deleted.
  • MiniMax Code 0.6.10 keeps ACP session MCP servers on the root session and starts task children without them. Its children therefore get none of the Session's functions or MCP servers, as in a local run.
• Child Items: a child's function Item now carries its function_call_output, mapped from the native tool result. The child's Items appear when the root Turn settles.
• Failures and races:
  • A child call whose child cannot be resolved fails the execution. It no longer reaches the model as a tool error.
  • The live read now reads the SDK first and the raw rows second, so a row native appends in between no longer fails the read.
  • A result delivered before an abort keeps its receipt obligation, as for a root call.
  • A result that arrives after its call was withdrawn is ignored.
• Verification:
  • Function calls were verified live with a real model on environment: none, both the call with its receipt and the withdrawal.
  • Child MCP calls are admitted and covered by unit tests only.
  • Hosted and self-hosted placements are admitted, not run live.

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