fix: accept folded block scalars in handoff YAML

[TheAmericanMaker]

Closes #211.

closeout_summary: >- is valid YAML and the natural choice for a wrapped prose field, but it failed with:

Invalid YAML indentation near: Mapped rel-mcp: one module, two pure exports, …

The parser handled only | and |-. A >- header fell through to the plain-scalar path, and the block body underneath it then failed the indentation check — so the error blamed whitespace when the cause was the scalar style. That sends you re-indenting instead of changing one character; it did exactly that to me.

It matters because a handoff is usually written by a model, and a model writing a wrapped prose field reaches for >-. Found during the 0.19.2 surface verification by writing a handoff by hand and hitting it on the first try.

The fix

Both block styles and all three chomping indicators — |, |-, |+, >, >-, >+ — with real folding semantics:

• a single line break between content lines becomes a space
• a run of k blank lines becomes k newlines
• more-indented lines keep their breaks, so a folded block can still carry an indented snippet without it being flattened onto one line

Literal blocks parse exactly as before; |+ is newly supported alongside them. A value that merely starts with an indicator (|x, > not a header) is still a plain scalar.

templates/phase-handoff.yaml said "YAML literal blocks are supported" — accurate before, incomplete now. It names both styles.

Verification

The exact handoff that failed during the 0.19.2 verification now parses:

closeout_summary: "Mapped rel-mcp: one module, two pure exports, no dependencies, no lifecycle, no state. Key hazard is ESM syntax without a module declaration. Routed arch-CF1 to contracts."

Six new tests in tests/yaml.test.mjs cover folding, all three chomping indicators, blank-line runs, more-indented lines, literal-block regression, and the not-a-header cases.

npm run build clean, 677/677 tests pass.

🤖 Generated with Claude Code