Remove CODEX_RS_SSE_FIXTURE test hook (#22413)

## Why

`CODEX_RS_SSE_FIXTURE` let integration-style CLI, exec, and TUI tests
bypass the normal Responses transport by reading SSE from local files.
That kept test-only behavior wired through production client code. The
affected tests can stay hermetic by using the existing
`core_test_support::responses` mock server and passing `openai_base_url`
instead.

## What Changed

- Removed the `CODEX_RS_SSE_FIXTURE` flag,
`codex_api::stream_from_fixture`, the `env-flags` dependency, and the
checked-in SSE fixture files.
- Repointed the affected core, exec, and TUI tests at `MockServer` with
the existing SSE event constructors.
- Removed the Bazel test data plumbing for the deleted fixtures and
refreshed cargo/Bazel lock state.

## Verification

- `cargo build -p codex-cli`
- `cargo test -p codex-api`
- `cargo test -p codex-core --test all responses_api_stream_cli`
- `cargo test -p codex-core --test all
integration_creates_and_checks_session_file`
- `cargo test -p codex-exec --test all ephemeral`
- `cargo test -p codex-exec --test all resume`
- `cargo test -p codex-tui --test all
resume_startup_does_not_consume_model_availability_nux_count`
- `just bazel-lock-update`
- `just bazel-lock-check`
- `just fix -p codex-api -p codex-core -p codex-exec -p codex-tui`
- `git diff --check`

codex-rs/core/src/client.rs

@@ -112,7 +112,6 @@ use crate::client_common::Prompt;
 use crate::client_common::ResponseEvent;
 use crate::client_common::ResponseStream;
 use crate::feedback_tags;
-use crate::flags::CODEX_RS_SSE_FIXTURE;
 use crate::util::emit_feedback_auth_recovery_tags;
 use codex_api::map_api_error;
 use codex_feedback::FeedbackRequestTags;
@@ -772,7 +771,6 @@ impl ModelClient {
     pub fn responses_websocket_enabled(&self) -> bool {
         if !self.state.provider.info().supports_websockets
             || self.state.disable_websockets.load(Ordering::Relaxed)
-            || (*CODEX_RS_SSE_FIXTURE).is_some()
         {
             return false;
         }
@@ -1194,8 +1192,7 @@ impl ModelClientSession {
 
     /// Streams a turn via the OpenAI Responses API.
     ///
-    /// Handles SSE fixtures, reasoning summaries, verbosity, and the
-    /// `text` controls used for output schemas.
+    /// Handles reasoning summaries, verbosity, and the `text` controls used for output schemas.
     #[allow(clippy::too_many_arguments)]
     #[instrument(
         name = "model_client.stream_responses_api",
@@ -1221,21 +1218,6 @@ impl ModelClientSession {
         turn_metadata_header: Option<&str>,
         inference_trace: &InferenceTraceContext,
     ) -> Result<ResponseStream> {
-        if let Some(path) = &*CODEX_RS_SSE_FIXTURE {
-            warn!(path, "Streaming from fixture");
-            let stream = codex_api::stream_from_fixture(
-                path,
-                self.client.state.provider.info().stream_idle_timeout(),
-            )
-            .map_err(map_api_error)?;
-            let (stream, _last_request_rx) = map_response_stream(
-                stream,
-                session_telemetry.clone(),
-                InferenceTraceAttempt::disabled(),
-            );
-            return Ok(stream);
-        }
-
         let auth_manager = self.client.state.provider.auth_manager();
         let mut auth_recovery = auth_manager
             .as_ref()

codex-rs/core/src/config/config_tests.rs

@@ -7250,8 +7250,7 @@ model_verbosity = "high"
 /// 2. as part of a profile, where the `--profile` is specified via a CLI
 ///    (or in the config file itself)
 /// 3. as an entry in `config.toml`, e.g. `model = "o3"`
-/// 4. the default value for a required field defined in code, e.g.,
-///    `crate::flags::OPENAI_DEFAULT_MODEL`
+/// 4. the default value for a required field defined in code.
 ///
 /// Note that profiles are the recommended way to specify a group of
 /// configuration options together.

codex-rs/core/src/flags.rs

@@ -1,6 +0,0 @@
-use env_flags::env_flags;
-
-env_flags! {
-    /// Fixture path for offline tests (see client.rs).
-    pub CODEX_RS_SSE_FIXTURE: Option<&str> = None;
-}

codex-rs/core/src/lib.rs

@@ -35,7 +35,6 @@ mod environment_selection;
 pub mod exec;
 pub mod exec_env;
 mod exec_policy;
-mod flags;
 #[cfg(test)]
 mod git_info_tests;
 mod goals;