docs(editing): define structural query edit boundary

[627150795]

Problem

Text search and ordinary editing cannot reliably distinguish syntax from comments or strings, while structural rewrites would introduce a new multi-file mutation authority.

Value

Define separate read-only structural query and preview-first mutation contracts with stale-file fail-closed behavior.

Approach

• Add docs/design/STRUCTURAL_QUERY_PREVIEW_EDIT_CONTRACT.md.
• Separate query, preview, and future apply capabilities.
• Define proposal identity, parser and limit partiality, path and child authority, multi-file recovery, and hash verification.
• Keep the first step design-only; do not add an AST parser, dependency, or runtime mutation.

Validation

• git diff --check
• bun run lint
• bun run typecheck

Impact

Documentation only. This is a focused design slice for #165 and does not implement an AST query or edit runtime.

Addresses #165

[tt-a1i]

Thank you for writing down this candidate. We are closing it under the future-capability disposition in #277. The PR remains the preserved research source, but OpenPI will not promote a protocol-only or candidate design into a repository contract before there is an active implementation or experiment with a fixed owner, revision, verifier, and acceptance evidence. This is not a content rejection, and no rebase is requested. Restart the work from the linked source Issue when that evidence frontier is ready.