Checking inherently needs an inference pass (~2.6x compile as a standalone
pass). But direct-link builds ALREADY run one inference pass for
specialization (run-passes' infer-top), so checking can ride along: set a
check-mode flag, turn checking? on during that existing pass, and collect
the diagnostics after — ~2% overhead measured on the ray tracer, vs 2.6x
for the separate pass.
So the checker now defaults to `warn` in direct-link builds (where it's
nearly free) and stays OFF in plain REPL/dev builds (no inference to ride,
no forced cost — opt in with JOLT_TYPE_CHECK there). JOLT_TYPE_CHECK still
overrides in both directions (off to disable, error to escalate).
It checks the POST-optimization IR, which matches what the optimized
program actually evaluates — scalar-replace only drops provably-pure code,
an accepted opt-mode divergence, so no real error is hidden. The loaders
enable position tracking whenever checking will run (env-selected or
direct-link). type-check! (the standalone pass) stays for plain builds;
both paths share report-diags!.
cli-test pins: plain build silent, direct-link warns by default,
JOLT_TYPE_CHECK=off disables. Gate green, suite 4718, runtime bench even.
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