Save Brainstorming Session as Design Document

The user has previously run /spec:brainstorm. Your task is to:

1. Locate the /spec:brainstorm invocation in the current session conversation history.
2. Collect all user and assistant messages AFTER that command.
3. Analyze the conversation to infer the main feature/topic being designed.
4. Transform the brainstorming content into a cohesive design document with clear sections.
5. Generate a short, descriptive slug (3-5 words, lowercase, hyphen-separated) from the main topic.
6. Get the current date in YYYY-MM-DD format.
7. Construct the filename as docs/designs/YYYY-MM-DD-.md.
8. If a file with that name already exists, adjust by either appending a suffix like -1, -2 or a short timestamp.
9. If the docs/designs directory does not exist, create it.
10. Use the write tool to create the file with the generated filename and design content.
11. At the end, print the final file path you wrote to.

If no /spec:brainstorm command is found in the history, use all messages from the beginning of the conversation instead.