fix(gateway): use relative redirects to preserve host and port

[gustavosbarreto]

Summary

• Add absolute_redirect off to the nginx server block so redirects (like /admin → /admin/) generate relative Location headers instead of absolute ones
• Fixes the redirect dropping the port when accessing the gateway on non-standard ports (e.g. localhost:8088/admin redirected to http://localhost/admin/ instead of /admin/)

Test plan

• Access curl -v localhost:8088/admin and verify Location header is /admin/ (relative) instead of http://localhost/admin/ (absolute)

[github-actions]

[medium] Good fix — absolute_redirect off; is the correct and idiomatic nginx directive for this problem.

One thing to consider: there is a second server block further down (the Enterprise WebEndpoints block, ~line 758) that does not get this directive. The architecture analysis suggests it's probably fine since that block only has a rewrite ... break (internal, no client redirect) + proxy_pass, so nginx shouldn't generate any client-facing redirects there. However, for defensive consistency, you might want to add it there too — it's a no-op if no redirects are generated, but protects against future changes to that block.

Up to you whether to apply it there as well; the current change is correct for the immediate fix.

[github-actions]

[medium — testing] The existing TestMain_smoke test in gateway/main_test.go already spins up the gateway container on a random mapped port (i.e., a non-standard port — the exact scenario this PR fixes). It currently only checks /healthcheck. This is a great opportunity to add a regression test for the redirect behavior:

Suggested change

	absolute_redirect off;
	absolute_redirect off;

The config line itself is fine — the suggestion here is to extend gateway/main_test.go with something like:

// Disable automatic redirect following to inspect the Location header.
noRedirectClient := http.Client{
    Timeout: 5 * time.Second,
    CheckRedirect: func(req *http.Request, via []*http.Request) error {
        return http.ErrUseLastResponse
    },
}

adminURL := baseURL + "/admin"
resp, err = noRedirectClient.Get(adminURL)
assert.NoError(t, err)
defer resp.Body.Close()

assert.Equal(t, http.StatusMovedPermanently, resp.StatusCode)

location := resp.Header.Get("Location")
assert.Equal(t, "/admin/", location, "Location header should be relative, not absolute")

This would catch regressions if absolute_redirect off is ever accidentally removed.

[github-actions]

Review Summary: Reviewed PR 5860 across 5 dimensions (Code Quality, Security, Testing, Go/TS Patterns, Architecture). Security: No issues - relative redirects are safer. Architecture: No breaking changes, no cloud/enterprise impact. 2 inline comments posted (medium severity): (1) Consider adding absolute_redirect off to the second server block for consistency, (2) Extend gateway/main_test.go smoke test to verify relative redirects. Overall a clean, well-targeted fix. I have provided feedback as inline comments. When ready for re-review, comment /review.