Algorithmically is it possible to pass only 'safe' interpreted code to the CPU? The majority of Javacript engines (Chakra, V8, Spidemonkey and JavasciptCore) are under a security-auditable FOSS license. Browsers claiming Spectre/Meltdown immunity would be in the next release notes, surely.

I'm not discounting that CPUs should operate correctly into the future but the current sandboxes would seem to rely on whims of a CPU's microcode. And the question for browser makers is whether to trust them.