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Closes the last behavioural gap. buzz-agent's most load-bearing non-standard behaviour -- the agent may not end its turn while its todo list has open items -- now works, with no changes to goose. Why not goose's hook system. Goose has a blocking Stop hook with exactly these semantics (agent.rs:2891-2917), but it is unreachable: hook_manager is private with a #[cfg(test)] setter, and hooks are otherwise discovered as subprocesses from <root>/.goose/plugins/*/hooks/hooks.json. The subprocess route looked viable until you notice where the answer lives -- buzz-dev-mcp's todo list is in-process state (todo.rs:49, a Mutex<Vec<Item>>) and that process's stdio is owned by goose. A hook binary goose spawns cannot see it, so a materialised hooks.json would produce a hook that always answers "no objection": worse than no hook, because it looks like it works. Instead we own the outer loop, so we ask the tool ourselves. Agent::dispatch_tool_call is public (agent.rs:1059). Between rounds we call _Stop on the same extension the model uses; on objection we re-enter reply() with the objection as an agent-visible/user-invisible message. Capped at 3 consecutive vetoes, mirroring goose's own stop_hook_block_cap. _PostCompact is wired to AgentEvent::HistoryReplaced and re-injects via steer(), which goose drains at the round boundary (agent.rs:1951-1974). Extension name is discovered by "___Stop" suffix rather than hardcoded -- buzz-acp derives it from the MCP binary's file stem (buzz-acp/src/lib.rs:4145), so it is not a fixed string. KNOWN DEVIATION: buzz-agent hid _-prefixed tools from the model (agent.rs:328-336) while still calling them itself. Goose's available_tools allowlist gates advertising and dispatch through the same cache (extension_manager.rs:1421, :1698), so hiding them would make them undispatchable and break the veto. They stay visible; a system-prompt extension tells the model not to call them. 4 new tests against the real fake-mcp binary (copied from crates/buzz-agent) counting provider generations: 2 objections => 3 calls, permanent objection capped at 4, no hook => 1 call, and discovery under a non-obvious extension name. 21 tests green. Signed-off-by: Michael Neale <michael.neale@gmail.com>