fix: resolve relative server action redirects

[NathanDrake2406]

Overview

Item	Details
Goal	Match Next.js server action redirect semantics for dot-relative redirects.
Core change	Resolve action redirect locations against the action initiation pathname and keep same-origin redirects on the App Router navigation path.
Boundary	Browser-visible App Router behavior, with focused helper coverage for URL resolution.
Primary files	packages/vinext/src/server/app-browser-action-result.ts, packages/vinext/src/server/app-browser-entry.ts, tests/e2e/app-router/nextjs-compat/server-actions-relative-redirect.spec.ts
Impact	Nested server actions that call redirect("./...") or redirect("../...") land on the same routes as Next.js and do not force a document reload for same-origin App Router navigation.

Why

Server action redirect locations are relative to the route that initiated the action, not to an arbitrary later browser document URL, and same-origin action redirects should remain in the App Router client navigation lifecycle. The previous path treated the raw x-action-redirect value as a hard navigation target, which could resolve nested ./subpage redirects incorrectly and drop client state.

Area	Principle / invariant	What this PR changes
URL resolution	Dot-relative action redirects resolve with Next.js directory-style semantics from the action route.	Adds a typed resolver for server action redirect locations.
Client navigation	Same-origin App Router action redirects should not require a document reload.	Routes internal redirects through the app navigation runtime when available.
Compatibility tests	Regression coverage should prove the user-visible contract.	Ports the upstream browser scenario into the app-router compat fixture.

What changed

Scenario	Before	After
redirect("./subpage") from a nested route	Could land on the parent route's subpage or reload the document.	Lands on the nested subpage, matching Next.js.
redirect("../subpage") from a nested route	Hard navigation could lose client state.	Uses App Router navigation and preserves the in-page marker.
External action redirect	Hard navigation.	Still hard navigation.

Validation

• PLAYWRIGHT_PROJECT=app-router pnpm run test:e2e -- tests/e2e/app-router/nextjs-compat/server-actions-relative-redirect.spec.ts
• vp test run tests/app-browser-entry.test.ts -t "server action"
• vp fmt --check packages/vinext/src/server/app-browser-action-result.ts packages/vinext/src/server/app-browser-entry.ts tests/app-browser-entry.test.ts tests/e2e/app-router/nextjs-compat/server-actions-relative-redirect.spec.ts tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/actions.ts tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/page.tsx tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subdir/page.tsx tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subdir/subpage/page.tsx tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subpage/page.tsx
• vp env exec --node 24 ./scripts/run-nextjs-deploy-suite.sh /Users/nathan/Projects/vinext/.refs/nextjs-v16.2.6 --retries 0 -c 1 --debug test/e2e/app-dir/server-actions-relative-redirect/server-actions-relative-redirect.test.ts
• vp check
• commit hook: format, lint/typecheck, knip --no-progress

Risk / compatibility

• Public API: no new public API.
• Runtime: same-origin action redirects now use the App Router navigation runtime when present, which matches existing client navigation behavior.
• External redirects: remain hard navigations.
• Fallback behavior: parse fallback remains a hard navigation after the existing dangerous-scheme guard.

References

Reference	Why it matters
Next.js upstream test	Defines the browser-visible compatibility scenario ported here.
Next.js action handler	Shows action redirects resolving relative locations from the current pathname before rendering the redirect result.
Next.js assignLocation	Shows client-side handling of dot-relative navigation locations using a directory-style base URL.

[pkg-pr-new]

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npm i https://pkg.pr.new/vinext@1579

commit: fb66919

[Copilot]

Pull request overview

Aligns vinext’s Server Action redirect handling with Next.js semantics for dot-relative locations, ensuring redirects resolve against the action initiation route and that same-origin redirects can stay on the App Router client navigation path (avoiding document reloads).

Changes:

• Added resolveServerActionRedirectLocation() to resolve dot-relative redirect targets against the server action initiation URL.
• Updated browser server-action redirect handling to route same-origin redirects through the navigation runtime when available, falling back to hard navigations otherwise.
• Added unit + Playwright E2E coverage and fixture pages for relative/absolute/multi-level redirects.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subpage/page.tsx	Adds a target page for root-level relative redirect assertions.
tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subdir/subpage/page.tsx	Adds a nested target page for subdir relative redirect assertions.
tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/subdir/page.tsx	Adds client UI buttons to trigger server actions from a nested route.
tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/page.tsx	Adds client UI buttons to trigger server actions from the root route.
tests/fixtures/app-basic/app/nextjs-compat/server-actions-relative-redirect/actions.ts	Adds server actions that redirect via ./, ../, and absolute targets.
tests/e2e/app-router/nextjs-compat/server-actions-relative-redirect.spec.ts	Adds Playwright regression coverage for Next.js-compatible relative redirect behavior and “no reload” expectation.
tests/app-browser-entry.test.ts	Adds unit tests for redirect URL resolution + internal/external classification.
packages/vinext/src/server/app-browser-entry.ts	Updates server action redirect handling to resolve dot-relative targets and use navigation runtime for same-origin redirects.
packages/vinext/src/server/app-browser-action-result.ts	Introduces helper to resolve action redirect locations with Next.js directory-style dot-relative semantics.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.