[Tabs] Fix React 18 roving tabindex and dedupe invalid-value warning

[Janpot]

Fixes the nightly-cron test_unit-react@18 failures in Tabs.test.js. Both reproduce only under React 18 (pass under React 19/next), and have separate causes.

1. useRovingTabIndex: active item not updating under React 18 (real bug)

<Tabs> did not move the roving tabIndex to the newly selected tab when the value prop changed under React 18 (confirmed with waitFor — it never converges, so it's a behavior bug, not test timing). React 18 is a supported peer dependency, so this affects real users.

The hook derived state from the activeItemId prop by mutating a ref during render:

const previousActiveItemIdPropRef = React.useRef(activeItemIdProp);
if (activeItemIdProp !== previousActiveItemIdPropRef.current) {
  previousActiveItemIdPropRef.current = activeItemIdProp; // mutating a ref during render
  ...
}

That isn't idempotent under StrictMode's double-render: React resets state between the two render invocations but preserves ref mutations, so on the replay the guard already sees the new value and skips the update. Switched to the documented "store the previous prop in state" pattern.

2. Tabs: invalid value warning logged from every effect

The invalid-value dev warning lives inside getTabsMeta, which runs from several effects, so it logged multiple times per mount and the count varied under React 18 StrictMode. Guarded it with a WeakMap keyed by the Tabs instance's ref, so the warning is logged once per instance (rather than once globally — a global flag would persist across instances/tests and suppress later warnings). The WeakMap is only referenced from process.env.NODE_ENV !== 'production' blocks and carries a /* @__PURE__ */ annotation, so minifiers drop it (and the allocation) from production builds. Simplified the test expectation accordingly.

Verification

useRovingTabIndex + Tabs + MenuList + Stepper + MobileStepper test suites pass under both react@18 (useReactVersion ^18) and react@next (19.3.0-canary).

[code-infra-dashboard]

Deploy preview

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Bundle size

Bundle	Parsed size	Gzip size
@mui/material	▼-9B(0.00%)	▼-5B(0.00%)
@mui/lab	0B(0.00%)	0B(0.00%)
@mui/private-theming	0B(0.00%)	0B(0.00%)
@mui/system	0B(0.00%)	0B(0.00%)
@mui/utils	0B(0.00%)	0B(0.00%)

Details of bundle changes

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