Revert compaction view block messages

This reverts 0a98ccb. A compaction sends the view, its closing tag, a
newline, and the task as one user message with the same joined bytes.
Each retry adds its note as one separate user message. The prompt path,
names, style, and summary-failure log stay unchanged.

After the split, compactions read 32.8% of input from the cache across
493 calls, against 31.9% across 183 calls before it. Imports read 30.7%.
The split adds code and messages for no measured gain.