Extract pure diffing functions into diff module

Acceptance Criteria

• New file runes/plan/src/diff.ts exists and contains all pure diffing functions
• diff.ts has zero imports from node:fs, node:path, or node:child_process
• diffAttributes(prev, curr) is exported from diff.ts with AttributeChange type
• diffCriteria(prev, curr) is exported from diff.ts with CriteriaChange type
• parseTagAttributes(line) is exported from diff.ts
• parseCheckboxes(content) is exported from diff.ts with ParsedCheckbox type
• hasResolutionSection(content) is exported from diff.ts
• history.ts imports from diff.ts and re-exports the types for backwards compatibility
• All existing imports from ./history continue to work (no breaking changes)
• Existing history tests pass without modification

Approach

1. Create diff.ts and move the five pure functions plus their types (AttributeChange, CriteriaChange, ParsedCheckbox) and supporting regex constants (TAG_ATTR_RE, CHECKBOX_RE, RESOLUTION_RE).
2. In history.ts, replace the moved code with imports: import { diffAttributes, diffCriteria, parseTagAttributes, parseCheckboxes, hasResolutionSection, type AttributeChange, type CriteriaChange, type ParsedCheckbox } from './diff.js' and re-export them.
3. Git transport functions (getFileCommits, getFileAtCommit, extractEntityHistory, getBatchCommits, extractBatchHistory, isShallowClone) and cache functions stay in history.ts.
4. Run existing tests to confirm no regressions.

Dependencies

None — independent of the scanner-core extraction.

References

• Edge Runtime Compatibility for Plan Package — Edge Runtime Compatibility for Plan Package
• Git-Native Entity History — Git-Native Entity History

Resolution

Completed: 2026-04-14

Branch: claude/edge-runtime-refactor-HOg8v

What was done

• Created runes/plan/src/diff.ts with all pure diffing functions (diffAttributes, diffCriteria, parseTagAttributes, parseCheckboxes, hasResolutionSection) and their types (AttributeChange, CriteriaChange, ParsedCheckbox)
• Updated runes/plan/src/history.ts to import from diff.ts and re-export all functions and types for backwards compatibility

Notes

• diff.ts has zero dependencies on Node.js APIs — only pure TypeScript
• All 31 history tests pass without modification