Webhook trigger: native action to start the next backlog TODO ticket

Webhook triggers can currently only do one thing on delivery: spawn an agent (or a team) and hand it a prompt. There is no way to make a webhook directly execute a built-in board action.

A common automation need is "when a PR merges (or CI goes green, or an issue closes), start the next TODO ticket" — i.e. the exact effect of clicking "Start Next" on the board (reorder the top eligible TODO ticket, respecting blockedBy, to position 0, then run backlog_start_next). Today the only way to wire that to a webhook is spawning a full LLM agent whose entire job is to call two mechanical MCP tools (backlog_reorder + backlog_start_next). That costs an agent boot, a prompt, tokens, and a tab someone has to notice and eventually close — for something that is really a deterministic Kanban operation with no judgment involved.

Proposal: add a new webhook trigger mode ("Board action" alongside today's "One agent" / "A team"), with a first action "Start next TODO ticket". On a valid, filtered delivery it performs the same effect as backlog_start_next directly, with no agent spawned and no LLM call. Keep signature verification, filter and anti-burst exactly as they work today for the agent/team modes.

AgentsRoom diagnostics

• App version: 1.186.0
• OS: linux 7.0.0-31-generic (x64)
• Agent CLI: claude
• App language: system

Problem to solve

Webhook triggers can only spawn an agent/team with a prompt. There's no built-in action, so automating a purely mechanical board operation (advance the TODO column on an external event) forces spinning up a full agent turn just to call backlog_reorder + backlog_start_next.

Proposed behavior

Add a webhook trigger mode 'Board action' (alongside 'One agent' / 'A team') with a 'Start next TODO ticket' action: on delivery, directly reorder the top eligible TODO ticket (respecting blockedBy) and run the equivalent of backlog_start_next. No agent spawned, no prompt, no LLM call. Same filter/anti-burst/signature verification as today.

Who benefits

Teams running a ticket-per-agent pipeline (one saved agent or team executes each backlog ticket) who want the board to self-advance on external events (PR merged, CI green, issue closed) without paying for an agent turn just to move the Kanban.

Acceptance criteria

Near-instant, zero-token trigger for a purely mechanical board action; one less agent tab to babysit per event; the existing agent/team modes remain for anything that needs judgment.