0364 — A non-cancellable lifecycle ctx is an error, with an explicit DisableGracefulShutdown opt-out

Context. Registering with context.Background() or TODO() (ctx.Done() == nil) would make graceful shutdown silently not exist. But a legitimate fire-and-forget persona exists: short-lived sequential scripts where Produce returning means committed and nothing is ever left to drain.

Decision. Register rejects a non-cancellable ctx with a multi-line teaching error — first line wraps ErrLifecycleContextNotCancellable for errors.Is, body shows both fixes as paste-able snippets. Fire-and-forget callers opt out explicitly via DisableGracefulShutdown: declared intent over the cargo-cult context.WithCancel ritual a bare error would breed. pkg/context.LifecycleContext() (SIGINT/SIGTERM via signal.NotifyContext) is the guided path the error points to, no-arg on purpose — anyone with a real parent ctx has outgrown the helper and uses stdlib directly.

Consequences. Known wart: the package name shadows stdlib context (import alias needed) — moot once the public API moves to root. The consumer got its own DisableGracefulShutdown with a different justification (“Consume’s ctx is my only off-switch” is a coherent style, not a script persona). The producer’s copy of the check and flag were deleted 2026-08-08 along with producer lifecycle capture; the consumer keeps its own.