--update runbook: graph.json backup instruction comes after the diff that needs it, so the graph diff never runs #4539

Version: 0.9.92 (v8 at 86c57be); also present in 0.9.91. All 14 split-platform references/update.md runbooks, plus the aider and devin monoliths.

Problem

The --update runbook ends with a "show the graph diff" block that runs after Step 4. It compares graphify-out/.graphify_old.json, a backup of the pre-update graph.json, with the merged extraction. The instruction that creates that backup sits after the diff block, at the end of the section:

After Step 4, show the graph diff:
  ...diff block reads .graphify_old.json...
Before the merge step, save the old graph: `cp graphify-out/graph.json graphify-out/.graphify_old.json`
Clean up after: `rm -f graphify-out/.graphify_old.json`

An agent that follows the runbook from top to bottom reaches the backup sentence only after Step 4 has rewritten graph.json. By then it's too late:

• If the agent never takes the backup, the diff block's if old_data: has no else, so the diff prints nothing at all. The user gets no diff and no sign that one was skipped.
• If it takes the backup on reaching the sentence, the "old" graph is already the new one, and the diff reports no changes.

Repro

1. Build a graph, change a code file, and run /graphify . --update, following references/update.md in order.
2. After Step 4 the diff block runs before any .graphify_old.json exists, and it prints nothing.

Expected

The backup is taken before the merge, and the diff block says so when the backup is missing instead of skipping silently.