Allow history and notes without experimental context capability (#47625)

## Why

Enabling `features.token_budget.use_history_notes_extension`, explicitly or through model defaults, rejected session startup when the model lacked `supports_experimental_context`, even with experimental mode disabled.

## What changed

Remove that startup restriction so token-budget history and notes can be used independently of the model's experimental context capability.

## Testing

Extend core tests to cover explicit configuration and model defaults on startup and cold resume, checking `new_context`, token-budget contexts, and `history_ingest_requested` metadata. Add app-server coverage for native history and notes tools and context-window hints without experimental context capability.

GitOrigin-RevId: 6157479aeb75ffd785b8d4b2f48b11c6f46e8f35

codex-rs/app-server/tests/suite/v2/history_notes_extension.rs

@@ -30,13 +30,15 @@ const THREAD_HINT: &str =
     "Recent notes (up to 5, most-recent first):\n- /root/notes/latest.md (2 lines, 14 UTF-8 bytes)";
 const BRIDGE_HINT: &str = "unstructured notes/thread_hint fixture result";
 
-#[test_case(true, 200, THREAD_HINT; "native_hint")]
-#[test_case(true, 200, ""; "no_notes")]
-#[test_case(true, 503, THREAD_HINT; "native_failure_does_not_use_bridge")]
-#[test_case(false, 200, THREAD_HINT; "bridge_hint")]
+#[test_case(true, true, 200, THREAD_HINT; "native_hint")]
+#[test_case(true, false, 200, THREAD_HINT; "native_hint_without_experimental_capability")]
+#[test_case(true, true, 200, ""; "no_notes")]
+#[test_case(true, true, 503, THREAD_HINT; "native_failure_does_not_use_bridge")]
+#[test_case(false, true, 200, THREAD_HINT; "bridge_hint")]
 #[tokio::test]
 async fn app_server_uses_configured_notes_backend_for_context_window_hints(
     use_history_notes_extension: bool,
+    supports_experimental_context: bool,
     hint_status: u16,
     hint_text: &str,
 ) -> Result<()> {
@@ -115,7 +117,7 @@ async fn app_server_uses_configured_notes_backend_for_context_window_hints(
     let codex_home = TempDir::new()?;
     let config = load_default_config_for_test(&codex_home).await;
     let mut model = codex_core::test_support::construct_model_info_offline("mock-model", &config);
-    model.supports_experimental_context = true;
+    model.supports_experimental_context = supports_experimental_context;
     let catalog_path = codex_home.path().join("models.json");
     std::fs::write(
         &catalog_path,
@@ -132,7 +134,7 @@ async fn app_server_uses_configured_notes_backend_for_context_window_hints(
         .with_provider_base_url(&format!("{}/backend-api/codex", server.uri()))
         .with_provider_config("supports_websockets = false\nrequires_openai_auth = true")
         .with_extra_config(&format!(
-            "[features.token_budget]\nenabled = true\nuse_history_notes_extension = {use_history_notes_extension}\n\n[mcp_servers.notes]\nurl = \"{}/mcp\"\nstartup_timeout_sec = 10\n",
+            "[features.context_management]\nexperimental_mode = false\n\n[features.token_budget]\nenabled = true\nuse_history_notes_extension = {use_history_notes_extension}\n\n[mcp_servers.notes]\nurl = \"{}/mcp\"\nstartup_timeout_sec = 10\n",
             server.uri(),
         ))
         .write(codex_home.path())?;

codex-rs/core/src/session/mod.rs

@@ -726,16 +726,6 @@ impl Session {
                 &model_info,
             )?;
             token_budget::apply_model_defaults(Arc::make_mut(&mut config), &model_info);
-            if config
-                .token_budget
-                .as_ref()
-                .is_some_and(|token_budget| token_budget.use_history_notes_extension)
-                && !model_info.supports_experimental_context
-            {
-                return Err(CodexErr::InvalidRequest(format!(
-                    "features.token_budget.use_history_notes_extension is not supported by model `{model}`; disable it or select a model that supports experimental context"
-                )));
-            }
         }
         let configured_config = Arc::clone(&config);
         let multi_agent_version = config.multi_agent_version_override().or_else(|| {

codex-rs/core/tests/suite/token_budget.rs

@@ -364,14 +364,14 @@ async fn experimental_context_requires_capable_model_and_codex_backend(
     Ok(())
 }
 
-#[test_case(false, true, false; "explicit_history_notes_unsupported")]
-#[test_case(false, true, true; "explicit_history_notes_supported")]
+#[test_case(false, true, false; "explicit_history_notes_without_experimental_capability")]
+#[test_case(false, true, true; "explicit_history_notes_with_experimental_capability")]
 #[test_case(false, false, false; "explicit_standalone_token_budget")]
-#[test_case(true, true, false; "model_default_history_notes_unsupported")]
-#[test_case(true, true, true; "model_default_history_notes_supported")]
+#[test_case(true, true, false; "model_default_history_notes_without_experimental_capability")]
+#[test_case(true, true, true; "model_default_history_notes_with_experimental_capability")]
 #[test_case(true, false, false; "model_default_standalone_token_budget")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn token_budget_history_notes_requires_capable_starting_model(
+async fn token_budget_history_notes_can_be_enabled_without_experimental_context(
     use_model_defaults: bool,
     use_history_notes: bool,
     supports_context: bool,
@@ -380,7 +380,7 @@ async fn token_budget_history_notes_requires_capable_starting_model(
 
     let server = start_mock_server().await;
     let backend_url = format!("{}/backend-api/codex", server.uri());
-    let result = test_codex()
+    let mut builder = test_codex()
         .with_auth(CodexAuth::from_external_chatgpt_tokens(
             "header.e30.signature",
             "account-123",
@@ -411,30 +411,50 @@ async fn token_budget_history_notes_requires_capable_starting_model(
         .with_config(move |config| {
             config.model_provider.base_url = Some(backend_url);
             config.model_context_window = Some(CONFIGURED_CONTEXT_WINDOW);
-        })
-        .build_with_auto_env(&server)
-        .await;
+        });
+    let test = builder.build_with_auto_env(&server).await?;
 
-    if use_history_notes && !supports_context {
-        let error = result
-            .err()
-            .expect("unsupported history/notes must fail at startup");
-        assert!(error.to_string().contains(
-            "features.token_budget.use_history_notes_extension is not supported by model `gpt-5.2`"
-        ));
-        return Ok(());
-    }
-
-    let test = result?;
-    let response = mount_sse_once(&server, sse_completed("resp-1")).await;
+    let response = mount_sse_sequence(
+        &server,
+        vec![sse_completed("resp-1"), sse_completed("resp-2")],
+    )
+    .await;
     test.submit_turn("inspect token-budget activation").await?;
-    let request = response.single_request();
-    assert!(
-        tool_names(&request)
-            .iter()
-            .any(|name| name == "new_context")
-    );
-    assert_eq!(token_budget_contexts(&request).len(), 1);
+    // Builder overrides are consumed by the initial build. Reapply the model and
+    // provider settings so the cold resume exercises the same activation defaults.
+    let initial_config = test.config.clone();
+    let resumed = builder
+        .with_config(move |config| {
+            config.model = initial_config.model;
+            config.model_catalog = initial_config.model_catalog;
+            config.model_provider = initial_config.model_provider;
+            config.model_context_window = initial_config.model_context_window;
+        })
+        .restart(&server, &test)
+        .await?;
+    resumed
+        .submit_turn("inspect token-budget activation after restart")
+        .await?;
+
+    let requests = response.requests();
+    assert_eq!(requests.len(), 2);
+    for request in requests {
+        assert!(
+            tool_names(&request)
+                .iter()
+                .any(|name| name == "new_context")
+        );
+        assert_eq!(token_budget_contexts(&request).len(), 1);
+        let turn_metadata: Value = serde_json::from_str(
+            &request
+                .header("x-codex-turn-metadata")
+                .expect("request should include turn metadata"),
+        )?;
+        assert_eq!(
+            turn_metadata["history_ingest_requested"].as_bool(),
+            use_history_notes.then_some(true)
+        );
+    }
     Ok(())
 }