Support thread-level originator overrides (#29477)

## Why

Work(TPP) threads can be launched from the Desktop app, but if they all
keep the Desktop app's default originator then downstream attribution
cannot distinguish local Work launches from cloud-backed Work launches.
`thread/start.serviceName` already carries that launch signal, while
`SessionMeta.originator` is the durable thread-level value that survives
resume and fork.

This change converts the Desktop Work service names into an effective
originator at thread creation time, persists that originator with the
thread, and keeps using it for later model requests and memory writes.

## What changed

- Map `CODEX_WORK_LOCAL` and `CODEX_WORK_CLOUD` service names to
per-thread originators, while preserving
`CODEX_INTERNAL_ORIGINATOR_OVERRIDE` as the highest-precedence override.
- Persist the effective originator in `SessionMeta.originator`, read it
back on resume/fork, and inherit the parent originator for subagent
spawns when there is no persisted session metadata.
- Handle truncated `SpawnAgentForkMode::LastNTurns` forks by falling
back to the live parent originator when the forked history no longer
includes `SessionMeta`.
- Thread the per-thread originator through Responses headers,
websocket/compaction request paths, thread-store creation, rollout
metadata, and memory stage-one telemetry.

## Verification

- `just test -p codex-core
agent::control::tests::spawn_thread_subagent_inherits_parent_originator_without_fork
agent::control::tests::spawn_thread_subagent_fork_last_n_turns_inherits_parent_originator_without_session_meta
thread_manager::tests::originator_override_precedes_service_name_remapping`
- `just test -p codex-core
agent::control::tests::resume_thread_subagent_restores_stored_metadata_and_effective_multi_agent_mode`
- `just test -p codex-memories-write`
- `just fix -p codex-core -p codex-memories-write`
- `git diff --check`

codex-rs/thread-store/src/in_memory.rs

@@ -118,6 +118,7 @@ mod tests {
                     parent_thread_id,
                     source: SessionSource::Exec,
                     thread_source: None,
+                    originator: "test_originator".to_string(),
                     base_instructions: BaseInstructions::default(),
                     dynamic_tools: Vec::new(),
                     multi_agent_version: None,
@@ -242,6 +243,7 @@ impl InMemoryThreadStore {
             agent_nickname: params.source.get_nickname(),
             agent_role: params.source.get_agent_role(),
             agent_path: params.source.get_agent_path().map(Into::into),
+            originator: params.originator.clone(),
             source: params.source.clone(),
             thread_source: params.thread_source.clone(),
             model_provider: Some(params.metadata.model_provider.clone()),

codex-rs/thread-store/src/local/create_thread.rs

@@ -33,6 +33,7 @@ pub(super) async fn create_thread(
             params.parent_thread_id,
             params.source,
             params.thread_source,
+            params.originator,
             params.base_instructions,
             params.dynamic_tools,
         )

codex-rs/thread-store/src/local/mod.rs

@@ -1130,6 +1130,7 @@ mod tests {
             parent_thread_id: None,
             source: SessionSource::Exec,
             thread_source: None,
+            originator: "test_originator".to_string(),
             base_instructions: BaseInstructions::default(),
             dynamic_tools: Vec::new(),
             multi_agent_version: None,

codex-rs/thread-store/src/types.rs

@@ -79,6 +79,8 @@ pub struct CreateThreadParams {
     pub source: SessionSource,
     /// Optional analytics source classification for this thread.
     pub thread_source: Option<ThreadSource>,
+    /// Effective originator used for this thread's Responses requests and analytics events.
+    pub originator: String,
     /// Base instructions persisted in session metadata.
     pub base_instructions: BaseInstructions,
     /// Dynamic tools available to the thread at startup.