Skip the Wrapper

The wrapper is the whole finding. vibium on PATH is not Vibium: it is a Node script that resolves a platform package and execFileSyncs the real native binary. Every vibium <verb> is two process spawns, and the first is a Node runtime boot — paid before any browser work begins.

On a near-empty command the shim costs ~118ms against ~10ms calling the platform binary directly. The gap is constant whatever the command does, which is what a runtime boot looks like and not what work looks like.

That per-call figure does not multiply into a journey total. On the flat profile 6 × 106.19ms predicts 637ms against 405ms measured, and the 232ms shortfall is 10.3× the campaign's own 22.6ms single-difference floor. The tax is partly self-refunding: the shim arm arrives at each post-navigate command ~107ms later, and a later-arriving call is a cheaper call.

Stated before running: if the delta is flat across groups, the refund story is wrong. It did not fire. after_poll is the discriminator — a post-navigate position that pays the FULL tax, which rules out 'post-navigate steps are simply different steps'.

The refund shrinks with page weight — but not to zero

A falsifier registered before running required the refund to vanish on a page with nothing to hydrate. It shrank monotonically, then stopped at 19.2ms — excluding zero. Hydration explains ~77%, not all.

The residual is Chrome's BiDi mapper, not the page

Chrome's WebDriver BiDi is a JS bundle in its own renderer, a target named BiDi-CDP Mapper. Probed over CDP, its context decays 9.4ms (95% CI [8.2, 13.8]) in the 150ms after a navigation; the page-context control -0.1ms. cli-v2/docs/TECHNIQUES.md:160-176

13 runs, 710 reps, 0 mismatches, saving 107.4–111.9ms per call at 40×–60× the measured noise floor. Every sweep was also run in reverse, so a direction effect could not hide in the result.

Spread 1.7% on the saving, 3.5% on the ratio. The 3 reverse-order runs land at 107.6–109.3ms, so there is no direction effect to explain. repro:README.md:163-172

+function maybeReplaceShimWithBinary(vibiumPath) {
+  if (os.platform() === 'win32') return 'skipped: win32';
+  if (isYarn())                 return 'skipped: yarn';
+  const shim = path.join(__dirname, 'bin', 'cli.js');
+  const tmp  = `${shim}.${process.pid}.tmp`;
+  try   { fs.linkSync(vibiumPath, tmp);
+          fs.renameSync(tmp, shim);   // atomic swap, keeps the shim on failure
+          return 'linked'; } catch { /* clean up tmp */ }
+}

Link then rename, so a failure never leaves a half-written entry point. Every skip path keeps the working shim. Guarded off on win32 · yarn · binary not a file · any link/rename error; on every skip it prints vibium: keeping the Node shim (<reason>) rather than failing the install.