Validate implicit API keys for Guardian Decisions (#59905)

## Why

Decisions uses a commercial endpoint, so implicitly inherited credentials must exclude FedRAMP API keys.

## What changed

Reject empty, whitespace-padded, and FedRAMP keys selected from cached authentication or `OPENAI_API_KEY`, returning a credentials error without rewriting the key. Explicit `CODEX_GUARDIAN_DECISIONS_API_KEY` overrides retain their existing behavior.

## Testing

Extend the cached-key precedence test to verify that FedRAMP project and service-account keys, including a whitespace-padded key, are rejected even when `OPENAI_API_KEY` provides a fallback.

GitOrigin-RevId: 8904b0e5b30662aaf7eb7535309b01c254bcbb82

codex-rs/ext/guardian-v2/src/async_scorer/decisions_tests.rs

@@ -160,6 +160,17 @@ fn decisions_prefers_cached_api_key_over_openai_env() -> anyhow::Result<()> {
         decisions_api_key("openai", /*base_url*/ None, &cached) == Ok(auth_key.into()),
         "cached API-key auth must take priority over OPENAI_API_KEY"
     );
+    for auth_key in [
+        "sk-proj-fedramp-synthetic",
+        "sk-svcacct-fedramp-synthetic",
+        " sk-proj-fedramp-synthetic",
+    ] {
+        let cached = AuthManager::from_auth_for_testing(CodexAuth::from_api_key(auth_key));
+        assert!(matches!(
+            decisions_api_key("openai", /*base_url*/ None, &cached),
+            Err(DecisionsError::Credentials)
+        ));
+    }
     Ok(())
 }
 

codex-rs/ext/guardian-v2/src/async_scorer/startup.rs

@@ -67,6 +67,7 @@ pub(super) fn decisions_api_key(
                 .and_then(CodexAuth::api_key)
                 .map(str::to_owned)
                 .or_else(codex_login::read_openai_api_key_from_env)
+                .filter(|key| valid_implicit_decisions_key(key))
                 .ok_or(DecisionsError::Credentials)
         }
         Err(std::env::VarError::NotPresent | std::env::VarError::NotUnicode(_)) => {
@@ -75,6 +76,11 @@ pub(super) fn decisions_api_key(
     }
 }
 
+// Decisions uses a commercial endpoint. Reject padded keys without rewriting credentials.
+pub(super) fn valid_implicit_decisions_key(key: &str) -> bool {
+    !key.is_empty() && key.trim() == key && !codex_login::auth::is_fedramp_api_key(key)
+}
+
 pub(super) async fn sampler_config(
     input: &ThreadStartInput<'_, Config>,
     manager: Option<Arc<ThreadManager>>,