fix(relay): make Code.gs header strip opt-in so Rust config is sole control

The comment in Code.gs and Config::strip_noise_response_headers claimed that
setting strip_noise_response_headers = false in config.toml would pass all
headers through "regardless of what Code.gs sends." This was wrong: with
STRIP_NOISE_RESPONSE_HEADERS = true in Code.gs those headers are removed from
the JSON before Rust receives it, so the Rust toggle cannot restore them.

Fix: change Code.gs STRIP_NOISE_RESPONSE_HEADERS default from true to false.
GAS-side stripping is now opt-in — operators who want the extra bandwidth
reduction can flip it manually after deploying. With the default false, the
Rust config.toml field is the single user-facing control that works correctly
end-to-end: strip_noise_response_headers = false shows raw headers in the
browser without requiring a simultaneous Code.gs redeploy.

Update comments in Code.gs, config.rs, and domain_fronter.rs to document
the relationship between the two layers accurately.

Author: CaptainMirage

assets/apps_script/Code.gs

@@ -52,14 +52,18 @@ const DIAGNOSTIC_MODE = false;
 // alt-svc, server-timing, etc. These add 400-700 bytes of JSON per response
 // for no benefit — the relay ignores them and the browser never reads them.
 //
-// STRIP_NOISE_RESPONSE_HEADERS controls whether _respHeaders() filters them
-// before returning. Hardcoded true here for GAS-side payload reduction.
 // The primary user toggle is `strip_noise_response_headers` in config.toml
-// on the Rust client side, which drops them even if Code.gs sends them.
+// on the Rust client side. That field controls what the browser sees and
+// works regardless of this constant.
 //
-// Set to false only if you need to see raw origin headers in GAS logs.
+// STRIP_NOISE_RESPONSE_HEADERS is a separate GAS-side optimization: when
+// true, headers are stripped before building the JSON payload, reducing the
+// data sent over the GAS -> Rust leg. Set to true only for extra bandwidth
+// savings. Leave false (the default) so the Rust config is the sole control
+// and `strip_noise_response_headers = false` in config.toml shows raw headers
+// without also requiring a Code.gs redeploy.
 // ---------------------------------------------------------------------------
-const STRIP_NOISE_RESPONSE_HEADERS = true;
+const STRIP_NOISE_RESPONSE_HEADERS = false;
 
 const STRIP_RESPONSE_HEADERS = {
   "report-to": 1, "reporting-endpoints": 1,

src/config.rs

@@ -439,8 +439,12 @@ pub struct Config {
     /// `server-timing` are attached by modern CDNs (Cloudflare, AWS,
     /// Fastly) and add 400–700 bytes per response for no benefit through
     /// a MITM relay — the proxy ignores them and the browser never reads
-    /// them. Default `true`. Set to `false` only to inspect raw origin
-    /// headers for debugging.
+    /// them. Default `true`. Set to `false` to pass all headers through.
+    ///
+    /// Note: `Code.gs` has a separate `STRIP_NOISE_RESPONSE_HEADERS`
+    /// constant (default `false`) that strips at the GAS side before the
+    /// JSON reaches Rust. To see fully raw headers in the browser, both
+    /// this field and the Code.gs constant must be `false`.
     #[serde(default = "default_strip_noise_response_headers")]
     pub strip_noise_response_headers: bool,
 }

src/domain_fronter.rs

@@ -415,7 +415,9 @@ pub struct DomainFronter {
     disable_padding: bool,
     /// Strip CDN noise headers (report-to, nel, alt-svc, etc.) from the
     /// relay response before forwarding to the browser. Default true.
-    /// Mirrors `Config::strip_noise_response_headers`.
+    /// Mirrors `Config::strip_noise_response_headers`. Independent of the
+    /// GAS-side `STRIP_NOISE_RESPONSE_HEADERS` constant in Code.gs — both
+    /// must be false to see fully raw headers.
     strip_noise_response_headers: bool,
     zstd_enabled: Arc<AtomicBool>,
     /// Per-instance auto-blacklist tuning. Mirrors `Config::auto_blacklist_*`