What
On Linux, Claude Code's sandbox (the protection that limits what commands it runs can touch) uses a small helper program called apply-seccomp. The search for a globally installed copy of it has been split out, and there is now a way to run that search in the background instead of blocking. Both ways remember the result once found.
On Linux, sandbox setup now waits for the background search unless seccomp.argv0 is set. The warning telling you to install @anthropic-ai/sandbox-runtime globally is unchanged.
Why
The background search may let Linux sandboxing find a globally installed apply-seccomp helper that the old lookup missed.
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Whether the set of folders searched for the helper actually changed is not known.