recv: None = peek, positive value = opt-in long-poll

old behavior: omitted wait_seconds fell through to the 30s
RECV_LONG_POLL_DEFAULT — claude calling 'is there anything in
my inbox right now?' between actions blocked the turn for half
a minute. flip the semantics: None (or 0) returns immediately,
positive value parks up to MAX (180s, unchanged). cleaner
'peek vs wait' distinction; tool descriptions + agent/manager
prompts updated to point at the new shape.

harness's own serve loops in hive-ag3nt + hive-m1nd relied on
the old default for their inbox poll. they now explicitly pass
wait_seconds: Some(180) to opt into the full park — same
effective behavior as before, just spelled out.

retires the matching TODO under Turn loop.

hive-ag3nt/prompts/manager.md

@@ -2,7 +2,7 @@ You are the hyperhive manager `{label}` in a multi-agent system. You coordinate
 
 Tools (hyperhive surface):
 
-- `mcp__hyperhive__recv(wait_seconds?)` — drain one more message from your inbox. Without `wait_seconds` it long-polls 30s. To **wait** when you have nothing else to do, call with a long wait (e.g. `wait_seconds: 180`, the max) — you'll wake instantly on new work, otherwise return after the timeout. Use this instead of ending the turn or sleeping in a Bash command.
+- `mcp__hyperhive__recv(wait_seconds?)` — drain one more message from your inbox. Without `wait_seconds` (or with `0`) it returns immediately — a cheap inbox peek you can drop between actions. To **wait** when you have nothing else to do, call with a long wait (e.g. `wait_seconds: 180`, the max) — you'll wake instantly on new work, otherwise return after the timeout. Use that instead of ending the turn or sleeping in a Bash command.
 - `mcp__hyperhive__send(to, body)` — message an agent (by name), another peer, or the operator (`operator` surfaces in the dashboard).
 - `mcp__hyperhive__request_spawn(name)` — queue a brand-new sub-agent for operator approval (≤9 char name).
 - `mcp__hyperhive__kill(name)` — graceful stop on a sub-agent. No approval required.