Extract pure scanner functions into scanner-core module

Acceptance Criteria

• New file runes/plan/src/scanner-core.ts exists and contains all pure scanner functions
• scanner-core.ts has zero imports from node:fs, node:path, node:child_process, or @refrakt-md/content
• parseFileContent(source, relPath) is exported from scanner-core.ts
• scanPlanSources(sources) is exported from scanner-core.ts
• All supporting pure functions (extractCriteria, extractResolution, extractRefs, extractScopedRefs, walkNodes, extractHeadingText, matchKnownSection, extractTitle) move to scanner-core.ts
• scanner.ts imports from scanner-core.ts and re-exports the pure functions alongside its filesystem functions
• All existing imports from ./scanner and the main entry point continue to work (no breaking changes)
• index.ts re-exports parseFileContent and scanPlanSources unchanged
• Existing tests pass without modification

Approach

1. Create scanner-core.ts and move all pure functions into it. Keep the Markdoc import (pure JS, no Node.js APIs) and any type imports from ./types.ts.
2. In scanner.ts, replace the moved function bodies with import { parseFileContent, scanPlanSources, ... } from './scanner-core.js' and export { parseFileContent, scanPlanSources } from './scanner-core.js'.
3. Filesystem-dependent functions (parseFile, scanPlanFiles, collectMdFiles, readCache, writeCache) stay in scanner.ts.
4. Verify that scanner.ts is the only file that imports node:fs, node:path, and @refrakt-md/content.
5. Run existing tests to confirm no regressions.

Dependencies

None — this is the first extraction step.

References

• Edge Runtime Compatibility for Plan Package — Edge Runtime Compatibility for Plan Package

Resolution

Completed: 2026-04-14

Branch: claude/edge-runtime-refactor-HOg8v

What was done

• Created runes/plan/src/scanner-core.ts with all pure scanner functions (parseFileContent, scanPlanSources, extractCriteria, extractResolution, extractRefs, extractScopedRefs, walkNodes, extractHeadingText, matchKnownSection, extractTitle, and supporting constants)
• Rewrote runes/plan/src/scanner.ts to import from scanner-core and re-export pure functions; kept only filesystem-dependent code (parseFile, scanPlanFiles, collectMdFiles, readCache, writeCache, getGitMtimes)
• index.ts re-exports unchanged — no breaking changes to public API

Notes

• scanner-core.ts depends only on @markdoc/markdoc (pure JS) and @refrakt-md/runes (escapeFenceTags only)
• All 321 plan tests pass without modification