Stage 6 review Obs 1b: the 300s default lived as a literal in two
places (DEFAULT_ASYNC_EXEC_TIMEOUT in dispatcher.rs and
DEFAULT_SAFE_VISIBILITY_VS_EXEC_BUDGET_SECS in triggers_api.rs). A
future change to the dispatcher would silently leave the
visibility-timeout warn threshold out of sync.
Extract a single pub const DEFAULT_ASYNC_EXEC_TIMEOUT_SECS: u32 = 300
in dispatcher.rs, derive the existing Duration constant from it, and
re-export it under the triggers_api name so the validator's
self-contained semantics are preserved at the call site. Tests still
inject the value explicitly via TEST_SAFE_LIMIT — no behavior change.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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