Feature request: automatically update project.md during archive #331

Describe the problem

When using OpenSpec in my projects, I noticed that after completing a change and running openspec archive, the tool merges the spec delta back into the openspec/specs directory. However, it does not touch openspec/project.md, which is meant to capture project-level conventions and context.

This means that any high-level conventions or architectural notes that emerge during a change have to be added manually after the archive. At the moment the only way to update project.md is to ask the AI assistant to "please fill in project.md" or to edit the file by hand. This creates an extra manual step and makes it easy for project.md to drift out of sync with the specs.

Proposed solution

It would be helpful if OpenSpec (and its supported AI tooling) could optionally update openspec/project.md during the archive step. For example, when archiving a change the CLI could:

• Include project-level context updates in the change proposal and apply them automatically.
• Or, inject a global instruction so that AI agents know to update project.md when finalising a change.

An automated or semi-automated mechanism would ensure that project-wide documentation stays up-to-date without requiring a separate manual prompt every time.

Additional context

I’m currently using the slash-command workflow (/openspec-proposal, /openspec-apply, /openspec-archive) with Codex, but this issue would apply to any AI tool. The goal is to reduce manual steps and keep project.md aligned with the archived specs.