fix: default redirect() to "push" in Server Action context

[NathanDrake2406]

Summary

• redirect() called inside a Server Action always used "replace" navigation, breaking the Back button after form submissions. Next.js defaults to "push" in action context (via actionAsyncStorage.getStore()?.isAction).
• Instead of adding a new AsyncLocalStorage, use an empty string sentinel in the digest when no explicit type is provided. The action handler resolves empty to "push", while SSR render contexts only extract location/statusCode (no type needed at HTTP level).
• Also adds an optional type parameter to permanentRedirect() matching the Next.js signature (defaults to "replace").

How it works

1. redirect("/foo") now produces digest NEXT_REDIRECT;;%2Ffoo (empty type field)
2. redirect("/foo", "push") produces NEXT_REDIRECT;push;%2Ffoo (explicit, always respected)
3. The action handler in app-rsc-entry.ts resolves empty to "push" (parts[1] || "push")
4. The browser entry reads x-action-redirect-type header and uses window.location.assign() for push / window.location.replace() for replace

Next.js reference

• packages/next/src/client/components/redirect.ts — line 43: type ??= actionAsyncStorage?.getStore()?.isAction ? 'push' : 'replace'
• packages/next/src/client/components/redirect.ts — line 62: permanentRedirect accepts optional type parameter

Test plan

• redirect() without explicit type produces empty sentinel in digest
• redirect() with explicit "push" or "replace" preserves type in digest
• Semicolon-in-URL encoding still prevents digest injection (updated assertion)
• permanentRedirect() accepts optional type parameter
• permanentRedirect() defaults to "replace" when no type given
• Generated action handler defaults empty type to "push" (template assertion)
• Entry template snapshots updated
• All existing redirect/error-boundary/route-handler tests pass

[pkg-pr-new]

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npm i https://pkg.pr.new/vinext@779

commit: df4b44a

[james-elicx]

/bigbonk review

[ask-bonk]

Good fix. The approach of deferring type resolution to the catch site via an empty sentinel is a pragmatic alternative to adding a new AsyncLocalStorage (which is what Next.js uses with actionAsyncStorage). The SSR catch sites (app-route-handler-policy.ts, app-page-execution.ts) only extract location and statusCode from the digest and ignore parts[1], so the empty sentinel is harmless there. The action handler correctly resolves empty to "push", and the browser entry already falls back to "replace" when the header is absent.

Tests are thorough — they cover the empty sentinel, explicit types, semicolon injection, permanentRedirect with optional type, and the generated template assertion. The permanentRedirect change correctly matches Next.js, which also defaults to "replace" without isAction context-dependence.

One minor observation and one question below, but neither blocks merging.

[ask-bonk]

Nit: worth noting a subtle difference from Next.js here. Next.js resolves the type at call time using actionAsyncStorage.getStore()?.isAction, so the digest always carries an explicit "push" or "replace". Vinext defers it to the catch site using an empty sentinel.

This works correctly today because the only catch site that cares about the type is the Server Action handler (which defaults empty → "push"). The SSR catch sites (app-page-execution.ts, app-route-handler-policy.ts) ignore the type field entirely.

If a future catch site needs the type and doesn't know whether it's in an action context, the sentinel approach would need revisiting. Not a blocker — just documenting the trade-off for future readers.

[ask-bonk]

Next.js also does not use isAction-dependent defaulting for permanentRedirect — it always defaults to "replace". This matches. Good.

[ask-bonk]

Review submitted. Here's a summary of my assessment:

Approved. The PR correctly fixes redirect() to default to "push" in Server Action context, matching Next.js behavior where the Back button should work after form submissions.

What the PR does well:

• Uses an empty sentinel in the digest (NEXT_REDIRECT;;%2Ffoo) to defer type resolution to the catch site, avoiding a new AsyncLocalStorage. This is a pragmatic design trade-off vs Next.js's actionAsyncStorage.getStore()?.isAction approach.
• The SSR catch sites (app-page-execution.ts, app-route-handler-policy.ts) only extract location and statusCode — they never read parts[1], so the empty sentinel is harmless.
• The browser entry (app-browser-entry.ts:526) already falls back to "replace" when the header is missing, providing correct default behavior for non-action contexts.
• permanentRedirect() correctly matches Next.js by always defaulting to "replace" (no action-context dependence), and the optional type parameter is added to match the full signature.
• Test coverage is thorough: empty sentinel, explicit types, semicolon injection, permanentRedirect with/without type, and generated template assertion.

One observation left as a comment: The sentinel approach differs from Next.js's call-time resolution. If a future catch site needs the type without knowing whether it's in an action context, this would need revisiting. Not blocking — just documented for future readers.

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