Replay a synthetic log through the core

Replay a synthetic log through the core

The exit check of the memory core runs a synthetic log of 100,000
messages through the core with the fake summarizer. The log mixes short
user lines, replies, notes, reports, tool calls, and tool output, and
one output in a hundred is over 30 KB. The core has no reader of the
optchat log, because that belongs to the history import.

After each message the test checks that the chat view is at most 128,000
bytes and the compaction view at most 32,000, and that a batch merges
the chat view to 64,000 bytes or less. It checks each rendered line: a
built line holds its node, a long message has a summary and not its
text, and an unbuilt line holds only the pending mark. A restart in the
middle and at the end loads the same views and view.json byte for byte.

Issue: beb9a70