[0.42-r2 H1] enhanced submit URL ignores form action — `submitter.formAction` is always truthy

[SisyphusZheng]

Severity: high · Category: implementation bug

Evidence. packages/adapter-vite/src/internal/ssg/entry-generators.ts (in __onSubmit): var actionUrl = (submitter && submitter.formAction) || form.action || window.location.href;. The formAction IDL attribute returns the DOCUMENT URL when the submitter has no formaction attribute, so it always wins over form.action.

Repro (verified in browser). Page at /live?x=1 with <form action="/other" method="post" data-open-enhance> and a plain submit button: submitter.formAction === http://host/live?x=1, so the enhanced POST goes to /live?x=1, while the native POST (no JS) correctly goes to /other — the two channels disagree (ADR-0120 rule 2).

Fix. Only honor formAction when the attribute is present: (submitter && submitter.hasAttribute('formaction') && submitter.formAction) || form.action || window.location.href.

Acceptance. e2e: enhanced submit of <form action="/other-route"> with an attribute-less submitter POSTs to /other-route; the formaction case keeps working.

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Filed from the 0.42 round-2 review (docs/audit/2026-07-28-alpha5-round2-review.md). Target line: 0.42.0-alpha.6.

[SisyphusZheng]

Fixed and shipped in v0.42.0-alpha.6 (npm dist-tags latest/alpha at 0.42.0-alpha.6, tag ccc9407). The fix and its regression test landed via PR #594 (fixture suite 49 tests × 3 engines = 147 green, including the new round-2 specs; unit + parity suites green).