tokio::time::timeout over JoinHandle only drops the future — the
spawn_blocking OS thread keeps running until the Rhai script self-
completes or hits the per-op budget. A `loop {}` body with a generous
max_operations could pin a blocking worker for tens of seconds; on Pi-
class hardware one anonymous-callable script call could permanently
subtract a worker from the pool.
Installs an `engine.on_progress` hook that consults a thread-local
deadline; when `Instant::now() >= deadline` the hook returns `Some(_)`,
triggering `ErrorTerminated` inside the Rhai loop. The deadline is set
by `Engine::execute_with_deadline` / `Engine::execute_ast_with_deadline`
via an RAII `DeadlineGuard`, called from the orchestrator client; the
old `execute` / `execute_ast` paths are unchanged so tests, validation,
and the parse-only path keep working.
Invoke re-entry (`sdk/invoke.rs`) inherits the parent's deadline
transparently — the thread-local is set for the entire spawn_blocking
lifetime, and Rhai is single-threaded so the same thread services the
parent + every sub-script.
New tests:
* `deadline_terminates_a_runaway_loop` — `loop {}` body with
`max_operations = u64::MAX` and a 100 ms deadline aborts within 2 s
(typically <200 ms). Maps to `ExecError::Runtime`.
* `no_deadline_set_does_not_abort` — `None` deadline keeps the pre-
audit behavior; the op-budget still bites.
Audit ref: security_audit/05_sandbox_exec.md#f-se-h-01.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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