Forward thread originators from standalone extensions (#33677)

## Why

Standalone web search and image requests need to preserve the trusted,
thread-scoped originator used for billing attribution.

## What changed

- Seed extension data with the resolved thread originator and recognize
  `codex_work_cca` and `chatgpt_cca` service names as originators.
- Forward non-default originators from the web search and image generation
  extensions with the shared originator-header helper.

## Testing

- Cover originator resolution, header validation, and forwarding for web
  search, image generation, and image editing.

GitOrigin-RevId: 165dace8e4d24e4bd92f234bff5ec77a21a7ff6e

codex-rs/ext/extension-api/src/contributors/thread_lifecycle.rs

@@ -2,6 +2,14 @@ use crate::ExtensionData;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::TurnEnvironmentSelection;
 
+/// Trusted, host-resolved billing attribution for a thread.
+///
+/// Extensions may forward this value to first-party APIs. It is seeded by Core
+/// after resolving persisted and host-provided originator state, rather than
+/// from model- or tool-controlled input.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ThreadOriginator(pub String);
+
 /// Input supplied when the host starts a runtime for a thread.
 pub struct ThreadStartInput<'a, C> {
     /// Host configuration visible at thread start.