[Bhekani Khumalo (bhekanik)]

What

Moves the duplicated frontmatterEnd into lib/sdk/markdown-scan.ts. Both copies are gone;
focus.ts and vault-updates.ts import it.

The comment on the vault-updates copy named its own duplicate in focus.ts and explained why it
had been left alone. That reason stopped applying when markdown-scan.ts landed.

How the two copies differed

Only in the parameter type:

-function frontmatterEnd(lines: string[]): number {          // focus.ts
+function frontmatterEnd(lines: readonly string[]): number { // vault-updates.ts

The bodies were byte-identical. The vault-updates signature is the one that moved, per the
instruction and because readonly string[] is the wider of the two; focus.ts passes a mutable
array, which satisfies it.

Verification

• bunx tsc --noEmit clean, bun run lint clean, anti-slop-check clean on changed lines.
• 818 tests passing before, 818 after. No test file is touched by this branch.
• git diff --stat: 16 insertions, 27 deletions across three files.

Observation, not changed

focus.ts has its own isArchivedHeading(line), a third variant of the archived-heading test that
markdown-scan.ts now owns for the other two files. It is not a copy: it accepts levels 2-6 only
(the others accept 1-6) and matches with a \b(?:ARCHIVED|HISTORICAL)\b regex against the raw
heading text rather than against canonicalised words. Folding it in would change behaviour, so it
needs its own decision rather than a move.