pgs: Duplicate `cache-control` headers when using `_headers` file

[imcotton]

When setting custom cache-control headers in the _headers file, pgs.sh returns two cache-control headers in the HTTP response:

1. The default cache-control from Souin middleware (e.g., max-age=60, must-revalidate)
2. The custom cache-control from _headers file (e.g., public, max-age=31536000, immutable)

This creates ambiguity for browsers and CDNs about which cache directives to follow.

Expected Behavior

Only one cache-control header should be present, with user-defined headers in _headers taking precedence over the middleware defaults.

Actual Behavior

Two cache-control headers are returned:

cache-control: max-age=60, must-revalidate
cache-control: public, max-age=31536000, immutable

Root Cause Analysis

The issue occurs because:

• Souin cache middleware sets a default CacheControl value
• User headers from _headers file are added using w.Header().Add(), which appends without overwriting
• The default cache control is configured from PGS_CACHE_CONTROL env var or defaults to max-age=600

Suggested Solution

When applying user headers from _headers, use w.Header().Set() instead of w.Header().Add() for the cache-control header to override the middleware's default. This would ensure user-defined cache directives take precedence while preserving the ability to set other custom headers.

[neurosnap]

This should be fixed, lemme know if you still notice this behavior.

[imcotton]

I tried again still got the same results, even with manually clear the server-side cache.

curl -Is https://bip39-recast.pgs.sh/assets/index-6e3dcd27.js | grep cache-control

cache-control: max-age=60, s-maxage=604800, must-revalidate
cache-control: public, max-age=31536000, immutable