Adds a single global concurrency cap on the data-plane dispatch path:
- orchestrator-core::gate::ExecutionGate wraps tokio::Semaphore.
Non-blocking try_acquire — no queue. PICLOUD_MAX_CONCURRENT_EXECUTIONS
env var (default 32) sets the cap.
- LocalExecutorClient acquires a permit before spawn_blocking; the
permit drops with the future so the slot returns automatically.
- On refusal, ExecError::Overloaded { retry_after_secs: 1 } surfaces
upward. ApiError::IntoResponse already maps that to 503 with a
Retry-After header (landed in the previous commit alongside the
variant itself).
- picloud binary constructs the gate once at build_app and shares it
with LocalExecutorClient.
The cap exists so a Rhai script storm can't drain the blocking-thread
pool — pushing back hard beats letting requests pile up against a
finite worker count. Per-app / per-script caps stay deferred until a
real workload demands them.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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