[johnhldiver-beep]

Fixes #308.

Setting Element.innerHTML or innerText to a non-string value threw instead of coercing like browsers do. Repro on base: innerHTML = 1 → this.buffers[0].slice is not a function; null/undefined → reading length of null/undefined; innerText had no setter at all (only a getter), so any assignment threw "which has only a getter".

Fix (one concern):

• esm/mixin/inner-html.js (+ cjs/ mirror): parseFromString(..., html === null ? '' : String(html)) — WebIDL LegacyNullToEmptyString semantics, so null → '' and everything else is String(value) (including undefined → "undefined"). This single function backs the Element setter, the ShadowRoot setter, and the outerHTML path, so all are fixed. The String import uses the repo's existing alias pattern from shared/utils.js.
• esm/interface/element.js (+ cjs/ mirror): new set innerText with the same coercion, replacing children like textContent does. The get innerText whitespace rules are untouched.
• style/text element own setters deliberately left alone — they route through textContent + Text coercion and do not throw on the same inputs (verified: style.innerHTML=1→"1", null→"", etc.).

Tests: regression tests in test/html/element.js for innerHTML = 1/null/undefined, innerText = 1/null, plus a normal-string sanity case. New tests failed before the fix (element test exit 1 with the expected buffers[0].slice TypeError); node test/html/element.js and the full node test/index.js suite both exit 0 with no failures after the fix. Honest limits: this suite prints no numeric assertion totals, so counts are reported as exit codes + failure-grep counts; eslint/tsc/rollup were not run (devDeps deliberately skipped for disk).

Note: prior PR #333 covered the same concern but was closed unmerged because its author voluntarily withdrew it to clean a backlog (2026-09-23) — not a maintainer rejection. Its author said he was "happy to come back later with a focused change", but that was 5+ weeks ago with no refile and the issue still OPEN, so this is not a live race.