A new boolean setting that causes Claude Code to exit with an error at startup if sandbox.enabled is true but the sandbox cannot start (missing dependencies, unsupported platform, or platform not in enabledPlatforms). When false (the default), a warning is logged but execution continues.
Evidence
Strict sandbox setting (search for "failIfUnavailable", "sandbox required but unavailable")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agreeAdded sandbox.failIfUnavailable setting to exit with an error when sandbox is enabled but cannot start, instead of running unsandboxed
