docs(tools): add ask_orchestrator and question denial documentation

- Add ask_orchestrator row to background tools table
- Document question tool denial for background tasks

docs/tools.md

@@ -15,8 +15,11 @@ Launch agents asynchronously and collect results later. This is how the Orchestr
 | Tool | Description |
 |------|-------------|
 | `background_task` | Launch an agent in a new session. `sync=true` blocks until complete; `sync=false` returns a task ID immediately |
-| `background_output` | Fetch the result of a background task by ID |
+| `background_output` | Fetch the result of a background task by ID. Surfaces questions relayed from subagents |
 | `background_cancel` | Abort a running background task |
+| `ask_orchestrator` | Non-blocking question relay for background subagents. Records a question for orchestrator review without waiting for an answer. Subagents state their assumption via `[ASSUMED: ...]` markers and continue working |
+
+Background subagents have the built-in `question` tool disabled (`question: false`) to prevent sessions from blocking on user input that never arrives. Instead, subagents use `ask_orchestrator` to relay questions to the orchestrator, who evaluates them when retrieving results via `background_output`.
 
 Background tasks integrate with [Multiplexer Integration](multiplexer-integration.md) — when multiplexer support is enabled, each background task spawns a pane so you can watch it live.