The runner's own writer of its consumer's oldest unacknowledged delivery is
replaced by mesh-sdk's consumer ledger: each message the hub hands a handler is
noted delivered, and applied when the handler acknowledges or ends it; one it
asks again stays unacknowledged. The key form is the same, a key per consumer
by its name in the state consumers. A runner that heard no event yet is healthy.
Builds: design 47 G §76, §468, §495; lead answers A-166, A-176
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h
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