Raise one ServiceNow problem for incidents with a shared cause

**Objective:** Raise one problem covering incidents `{incident-numbers}`, owned by `{assignment-group}` (default: the group most of the incidents belong to), with a root cause analysis task.

**Step 1: Read the incidents**

Call `servicenow-get-incident` with number set to each incident in `{incident-numbers}`. Collect priority, configuration-item, service, category, assignment-group and short-description.

**Step 2: Check they belong together**

If the incidents share no configuration-item, service or clear symptom, say so and ask the user to confirm they are related before going on.

**Step 3: Check for an existing problem**

Call `servicenow-get-problem` with short-description.contains set to the shared CI name or key words. If an open problem already covers them, report its number and stop.

**Step 4: Draft and confirm**

Propose:

* short-description: the shared symptom and CI in one line
* description: the list of incident numbers with their opened dates and short-descriptions
* configuration-item and business-service from the incidents when they agree
* impact and urgency: the highest seen across the incidents
* assignment-group: `{assignment-group}` or the most common group

Show this and ask for an explicit yes.

**Step 5: Write, in this order**

1. Call `servicenow-add-problem` once with the confirmed values.
2. Call `servicenow-get-problem` with short-description.contains set to the new short-description and opened.from today to get its number and sys-id.
3. Call `servicenow-add-problem-task` once with problem set to that sys-id, type Root cause analysis if listed, the same assignment-group, and short-description "Root cause analysis for <problem number>".

**Step 6: Report**

The problem number, the RCA task number (read it back with `servicenow-get-problem-task` using problem set to the problem number), and the incidents it covers.

**Rules & Guidelines:**

* Write tools allowed: `servicenow-add-problem` once and `servicenow-add-problem-task` once, after one confirmation. Do not call `servicenow-update-incident` or `servicenow-update-problem`; this tool set cannot link incidents to a problem, so list the incident numbers in the description instead and say so in the report.
* If step 5.2 cannot find the new problem, stop and report; never create a second one.

**Validation:**

* If any incident number is not found, list it and ask whether to continue without it.