Under the hood
New internal diagnostics track the first message's shape to diagnose cache breaks.
Prompt-cache-break diagnostics now capture a structured shape of the first message per cache source, covering block kinds, lengths, hashes, named sections, and worker-tool counts. When a cache break is attributed to the first message, this shape is diffed against the previous call, adding msg0Sections, msg0ChangedSections, msg0AddedSections/RemovedSections, and msg0ChangedBlocks to the break-diagnosis telemetry.