Archive workflows miss incomplete tasks in custom schema paths #1948

What happens

The single and bulk archive workflows look for tasks.md or an artifact named tasks. A custom schema can track task checkboxes under another artifact and path, such as implementation at planning/work-items.md. In that case, the workflows can report no tasks and proceed without warning about unchecked items.

Reproduction

Define a schema whose apply.tracks points to a nonstandard task file or glob. Add an unchecked task to a change using that schema, then follow /opsx:archive or /opsx:bulk-archive. The current guidance does not reliably find those checkboxes.

Expected

Both workflows use the selected change's totalTasks and completedTasks from openspec list --json with the same root or store selection. They warn for incomplete tasks and stop if the lookup fails.

This issue covers the workflow guidance; the CLI already resolves schema-tracked task files.