Add a pre-submit semantic cleanup checkpoint before verify/archive #1073

Problem

OpenSpec is effective at structuring changes through proposal, design, tasks, implementation, verification, and archive. However, AI-assisted implementation often leaves behind artifacts from earlier planning stages that are no longer part of the real implementation.

Examples include:

• unused API functions created from early assumptions
• type fields that never reach UI, validation, submission, or persistence
• store state, refs, computed values, watchers, or helpers that no longer serve the final data flow
• placeholder URLs, mock branches, temporary serialization logic, or debug code
• duplicated field mappings caused by earlier uncertainty
• planned extension points that were never connected to any remaining task

These artifacts can still pass lint, type checking, tests, and even OpenSpec verification, because they are syntactically valid and may not violate the written spec. The problem is semantic: the final implementation and the earlier planning residue have drifted apart.

Proposal

Introduce an optional pre-submit semantic cleanup checkpoint in the OpenSpec workflow, placed after the core implementation is complete and before verify / archive.

This checkpoint should audit the actual implementation against the active OpenSpec artifacts and identify code that no longer serves the real change.

Suggested lifecycle:

proposal/design/tasks
-> implementation
-> pre-submit cleanup audit
-> remaining implementation / integration
-> optional cleanup of confirmed redundant items
-> lint / typecheck / manual regression
-> openspec verify
-> archive