- Changed multiline payload syntax so continuation lines must start with `+`; that prefix is stripped before writing.
- Raw unprefixed lines after an op now throw an error instead of being silently accepted as payload.
- Removed `PAYLOAD_LINE_PREFIX_DEMOTED_WARNING` and the nested-replace demotion path; inner `N:` ops inside a pending `A-B:` now raise an overlap error.
- Raw blank lines between ops are ignored; use `+` alone for an empty payload line.
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