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Two "unknown tool (not in this turn's tool set)" failures, one disease: the turn's tool set was rebuilt from a different recipe depending on which entry point happened to drive it. A sub-agent got `ask_user_clarification`, `execute_subtask` and `activate_tools` and nothing else — while `agents/common/tools.md` and every reporting agent's prompt tell it to register its output with `update_scratchpad`. The child could see the scratchpad injected into its context but had no way to write to it. It now gets the scratchpad and todos tools, on the parent's `scratchpad_sid`: one blackboard per session, as the surrounding code already declared. `show_file_to_user` was injected per message by the WS handler, while `resume_session` and `resolve_pending_call` rebuilt the list with `execute_task` alone. So approving a card, or reconnecting mid-turn, continued the *same* conversation with the tool silently gone. There is now a single recipe, `ChatHub::session_interface_tools`, used by all three paths and fed by a builder the shell installs once through `Skald::set_interface_tools_builder`: the core keeps owning the tool, the shell keeps owning the policy of who gets it — Telegram still does not, since it cannot act on OpenFile.