Handle copied credentials in the broker and shell snapshots (#44038)

## Why

Shell startup can copy a credential into another variable and unset its original source. These aliases need credential brokering without losing source restrictions or mistaking ordinary shell content for credentials.

## What changed

- Discover supported GitHub and OpenAI credentials embedded in environment values, even without their canonical variables. Preserve source ownership so unbound enterprise tokens cannot acquire a default host binding.
- Redact unregistered supported credentials during text virtualization, distinguish adjacent credentials, and avoid matching unrelated provider prefixes and common hashed paths.
- Expose helpers for checking allowed credential sources and restoring known dummy credentials in trusted text for fail-open execution.
- Render allowed credential aliases as snapshot exports and replace known credential values in shell state, preserving exported functions and credential-shaped function names.

## Testing

Add regression coverage for copied aliases, enterprise host binding, source filtering, adjacent tokens, path false positives, and dummy restoration. Add a Bash snapshot test that preserves exported functions while replacing credentials in heredoc content.

GitOrigin-RevId: f1c3d531405a96ac6bfa3882a11b74643fa6f123

codex-rs/network-proxy/src/runtime.rs

@@ -477,6 +477,10 @@ impl NetworkProxyState {
         self.credential_broker.virtualize_text(text, env)
     }
 
+    pub(crate) fn restore_brokered_text(&self, text: &mut String) -> bool {
+        self.credential_broker.restore_text(text)
+    }
+
     pub fn inject_request_credentials(&self, host: &str, headers: &mut rama_http::HeaderMap) {
         self.credential_broker.inject_request_headers(host, headers);
     }