The contract already documents the scale-to-zero PRIMITIVES (§3.2 going-idle/
buffered-flip, §3.3 wake poke) and what's out of scope. This adds the missing
half: the contract FROM the primitives TO the behaviour layer — the guarantees
a separate scale-to-zero workstream must honour to consume them safely (register
a wakeUrl before suspend; drain+ack before teardown; keep the reconnect loop
live; treat suspended != down in the health model; don't assume exactly-once/
prompt wake; suspend only when genuinely idle, composing with the existing drain
machine). Docs-only; lets the independent scale-to-zero stream build against a
written contract instead of re-reading the connector.
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