Let agents cancel open questions; fix snapshots missing same-size edits

docs/operations.md

@@ -102,7 +102,7 @@ The task switcher (⌘K, or the navbar crumb) lists active tasks with their sess
 
 ## Inbox
 
-Agents ask questions with the `ask_human` MCP tool. Each question carries a `context` with the background the human needs to answer without reading the transcript; the UI renders it, the question, and the options as Markdown. A malformed call (no `context` or `why_blocked`, fewer than two options, a recommendation that isn't one of the options, an unknown attachment kind, a foreign `thread_id`) is rejected with a message saying what to fix, and nothing is filed. Each turn's final message (as a `report`) and each agent error (a turn that ends in error without a human interrupt, a process that dies mid-turn) also files an item.
+Agents ask questions with the `ask_human` MCP tool. Each question carries a `context` with the background the human needs to answer without reading the transcript; the UI renders it, the question, and the options as Markdown. A malformed call (no `context` or `why_blocked`, fewer than two options, a recommendation that isn't one of the options, an unknown attachment kind, a foreign `thread_id`) is rejected with a message saying what to fix, and nothing is filed. The call returns the item's id as `question_id`. An agent withdraws a question it no longer needs answered (the human answered it in a chat message, say) with the `cancel_question` MCP tool and that id: an `open` question of its own session becomes `dismissed` with no `resolved_by` (its `inbox.updated` event has actor `agent`), which also stops a blocking one from holding back delivery; anything else is rejected with a message saying why. Each turn's final message (as a `report`) and each agent error (a turn that ends in error without a human interrupt, a process that dies mid-turn) also files an item.
 
 `GET /api/inbox` is one query over open, unsnoozed items, oldest first; `project_id` and `task_id` narrow it to a project or task view, and `state` and `include_snoozed` widen it. Blocking questions and errors are `blocked`; reports and non-blocking questions are `fyi`. The inbox view groups items by task, each group headed by project and task: tasks with a blocked item come first, then tasks sort by project name and by their oldest item. Within a task, items are in time order.