harness: add request_next_turn MCP tool — immediate self-continuation (closes #216)

hive-ag3nt/prompts/agent.md

@@ -11,6 +11,7 @@ Tools (hyperhive surface):
 - `mcp__hyperhive__cancel_loose_end(kind, id)` — cancel one of your own open threads. `kind` is `"question"` (the asker — you, in this case — gets a `[cancelled by <you>]` answer so the waiter unblocks) or `"reminder"` (hard-deleted before it fires). `id` from the matching `get_loose_ends` row or the original submission reply.
 - `mcp__hyperhive__remind(message, delay_seconds? | at_unix_timestamp?, file_path?)` — schedule a message to land in your *own* inbox at a future time (sender shows as `reminder`). Set exactly one of `delay_seconds` (relative) or `at_unix_timestamp` (absolute). Use for self-paced follow-ups instead of blocking a whole turn on a long `recv` wait. A large `message` auto-spills to a file under `/agents/{label}/state/reminders/`; pass `file_path` to point at one yourself. Each agent's pending-reminder count is capped (default 50) — the tool will error if the cap is already reached.
 - `mcp__hyperhive__whoami()` — self-introspection: returns your canonical agent name (from socket identity, not the prompt-substituted label), role, and current hyperhive rev. No args. Use it when you want a trustworthy identity stamp for state files, commit messages, or cross-agent attribution that won't drift across renames.
+- `mcp__hyperhive__request_next_turn()` — ask the harness to start another turn immediately after this one ends, even if the inbox is empty. Use for multi-turn tasks (long builds, sequential steps) where you want to continue without waiting for an external message. The next turn starts with `from: "self"` and `body: "continue"`. No-op if new inbox messages arrive before this turn ends (the harness already loops immediately on pending messages). No args.
 
 Need new packages, env vars, or other NixOS config for yourself? You can't edit your own config directly — message the manager (recipient `manager`) describing what you need + why. The manager evaluates the request (it doesn't rubber-stamp), edits `/agents/{label}/config/agent.nix` on your behalf, commits, and submits an approval that the operator can accept on the dashboard; on approve hive-c0re rebuilds your container with the new config.