[0.155 hotfix] Restore none as the TUI reasoning summary default (#46467)

New local TUI sessions in 0.155 request detailed reasoning summaries by
default, which causes request rejection on providers that do not support
reasoning summaries. Restore `none` as the default while honoring
explicit `auto`, `concise`, and `detailed` settings and concurrent
delivery when summaries are explicitly enabled.

This focused backport targets `release/0.155`, based on the content
commit for `rust-v0.155.0`. It includes regression coverage for
new-thread settings and the outbound Responses request.

Validation:
- Patch applies cleanly to the 0.155 release source; `git diff --check`
passes.
- All 9 focused reasoning-default and reasoning-status tests passed,
including the outbound Responses request and existing snapshots.
- `just fmt` completed; the hotfix Rust files were unchanged. Unrelated
justfile rewrites from the locally installed formatter were discarded.
- All 4,589 non-ignored TUI tests passed across the rerun and a
follow-up of the remaining 196 tests after a runner disconnection. The
earlier cursor failures were caused by `NO_COLOR=1` / `TERM=dumb`; the
tests pass with normal terminal settings and no code or snapshot
changes.
- Release-build checks passed on Linux, macOS, and Windows.

CI currently reports failures in unchanged release-base files:
-
[Codespell](https://github.com/openai/codex/actions/runs/35380630185/job/105715678757)
flags the existing `OFlags::WRONLY` identifier.
- [Manifest
validation](https://github.com/openai/codex/actions/runs/35380630185/job/105715679235)
finds a stale feature exception for `codex-rs/code-mode/Cargo.toml`.
- [Dependency
audit](https://github.com/openai/codex/actions/runs/35380630185/job/105715679009)
reports RUSTSEC-2026-0285 for the existing `rustls 0.23.36` lockfile
entry.
- [cargo
shear](https://github.com/openai/codex/actions/runs/35380630185/job/105716110806)
reports an existing unlinked file,
`codex-rs/login/src/internal_identity.rs`.

Additional CI failures are also outside the changed TUI files: an unused
`body_json` import in `core/tests/suite/openai_file_mcp.rs` (Bazel
Clippy), a format-driver expectation in the Python SDK tests, and a
transient `Text file busy` error while spawning a code-mode test helper
(musl). These paths are unchanged from the release base.

codex-rs/tui/src/app_server_session.rs

@@ -1913,7 +1913,7 @@ fn new_thread_reasoning_overrides(config: &Config) -> Option<HashMap<String, ser
     let mut overrides = config_request_overrides_from_config(config).unwrap_or_default();
     let summary = config
         .model_reasoning_summary
-        .unwrap_or(codex_protocol::config_types::ReasoningSummary::Detailed);
+        .unwrap_or(codex_protocol::config_types::ReasoningSummary::None);
     overrides.insert(
         "model_reasoning_summary".to_string(),
         serde_json::Value::String(summary.to_string()),

codex-rs/tui/src/app_server_session/reasoning_defaults_tests.rs

@@ -10,14 +10,24 @@ use serde_json::json;
 #[tokio::test]
 async fn embedded_reasoning_defaults_reach_responses() -> Result<()> {
     for (settings, summary, stream_options) in [
-        ("", json!("detailed"), json!(null)),
+        ("", json!(null), json!(null)),
         (
             "[features]\nconcurrent_reasoning_summaries = false",
-            json!("detailed"),
+            json!(null),
             json!(null),
         ),
         (
             "[features]\nconcurrent_reasoning_summaries = true",
+            json!(null),
+            json!(null),
+        ),
+        (
+            "model_reasoning_summary = 'detailed'",
+            json!("detailed"),
+            json!(null),
+        ),
+        (
+            "model_reasoning_summary = 'detailed'\n[features]\nconcurrent_reasoning_summaries = true",
             json!("detailed"),
             json!({"reasoning_summary_delivery": "sequential_cutoff"}),
         ),
@@ -102,12 +112,19 @@ stream_max_retries = 0
 }
 
 #[tokio::test]
-async fn new_tui_threads_request_summaries_unless_explicitly_disabled() {
+async fn new_tui_threads_disable_summaries_unless_explicitly_enabled() {
     let temp_dir = tempfile::tempdir().expect("tempdir");
     for (config_text, expected_summary, expected_concurrent) in [
-        ("", "detailed", false),
+        ("", "none", false),
         (
             "[features]\nconcurrent_reasoning_summaries = true",
+            "none",
+            false,
+        ),
+        ("model_reasoning_summary = 'auto'", "auto", false),
+        ("model_reasoning_summary = 'detailed'", "detailed", false),
+        (
+            "model_reasoning_summary = 'detailed'\n[features]\nconcurrent_reasoning_summaries = true",
             "detailed",
             true,
         ),