A | block scalar loses its trailing newline when it is the last key in the frontmatter (and CombineFrontmatter rewrites it as >-) #153

What's wrong

The text handed to the YAML parser has its final line ending removed, so the same YAML parses differently depending on where a key sits:

• TrySplitFrontmatterBlocks slices each block to lines[close - 1].End (Frontmatter/Frontmatter.cs, ~lines 385–387), which excludes the last line's line ending.
• The parse path then does string section = block.Trim(); (~line 329).

A literal (|) or keep (|+) block scalar on the last key therefore loses its trailing newline(s).

Repro

Frontmatter.ExtractFrontmatter("---\ntitle: T\nnotes: |\n  line1\n  line2\n---\nbody\n");
// notes = "line1\nline2"      <- clip chomping should give "line1\nline2\n"

Frontmatter.ExtractFrontmatter("---\nnotes: |\n  line1\n  line2\ntitle: T\n---\nbody\n");
// notes = "line1\nline2\n"    <- correct, only because another key follows

// keep chomping: "---\ncode: |+\n  x = 1\n\n\n---\nbody\n"
// code = "x = 1"   (YamlDotNet on the same YAML directly gives "x = 1\n\n\n")

CombineFrontmatter on the first document writes the value back as

notes: >-
  line1

  line2

so the trailing newline is permanently lost from the file, and the scalar style changes on what should be a no-op round trip.

Why it matters

Moving a key, or adding one after it, changes its value. Consumers that rely on a trailing newline (code snippets, |+ content, text compared byte-for-byte) get different data. Every CombineFrontmatter pass also rewrites the file.

Suggested fix

Parse the block with its final line ending kept: slice to lines[close].Start instead of lines[close - 1].End. Use string.IsNullOrWhiteSpace only for the empty-block check, and don't Trim() the text that gets parsed. Leading Trim() also strips first-line indentation, which would break uniformly indented frontmatter.

Acceptance criteria

• notes parses to "line1\nline2\n" regardless of key position.
• The |+ example yields "x = 1\n\n\n".
• Combine with AsIs naming and no merging leaves a trailing | block's value unchanged.