Support remote compaction for Azure responses providers (#17958)

Azure Responses providers were still falling back to local compaction
because the compaction gate only checked
`ModelProviderInfo::is_openai()`.

Move the capability check onto `ModelProviderInfo` with
`supports_remote_compaction()`, backed by the existing Azure Responses
endpoint detection used in `codex-api`, and have `core::compact`
delegate to that helper.

Add regression coverage for:
- OpenAI providers using remote compaction
- Azure providers using remote compaction
- non-OpenAI/non-Azure providers staying on the local path

resolves #17773

---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

codex-rs/model-provider-info/src/lib.rs

@@ -7,6 +7,7 @@
 
 use codex_api::Provider as ApiProvider;
 use codex_api::RetryConfig as ApiRetryConfig;
+use codex_api::is_azure_responses_provider;
 use codex_app_server_protocol::AuthMode;
 use codex_protocol::config_types::ModelProviderAuthInfo;
 use codex_protocol::error::CodexErr;
@@ -300,6 +301,10 @@ impl ModelProviderInfo {
         self.name == OPENAI_PROVIDER_NAME
     }
 
+    pub fn supports_remote_compaction(&self) -> bool {
+        self.is_openai() || is_azure_responses_provider(&self.name, self.base_url.as_deref())
+    }
+
     pub fn has_command_auth(&self) -> bool {
         self.auth.is_some()
     }

codex-rs/model-provider-info/src/model_provider_info_tests.rs

@@ -129,6 +129,61 @@ supports_websockets = true
     assert_eq!(provider.websocket_connect_timeout_ms, Some(15_000));
 }
 
+#[test]
+fn test_supports_remote_compaction_for_openai() {
+    let provider = ModelProviderInfo::create_openai_provider(/*base_url*/ None);
+
+    assert!(provider.supports_remote_compaction());
+}
+
+#[test]
+fn test_supports_remote_compaction_for_azure_name() {
+    let provider = ModelProviderInfo {
+        name: "Azure".into(),
+        base_url: Some("https://example.com/openai".into()),
+        env_key: Some("AZURE_OPENAI_API_KEY".into()),
+        env_key_instructions: None,
+        experimental_bearer_token: None,
+        auth: None,
+        wire_api: WireApi::Responses,
+        query_params: None,
+        http_headers: None,
+        env_http_headers: None,
+        request_max_retries: None,
+        stream_max_retries: None,
+        stream_idle_timeout_ms: None,
+        websocket_connect_timeout_ms: None,
+        requires_openai_auth: false,
+        supports_websockets: false,
+    };
+
+    assert!(provider.supports_remote_compaction());
+}
+
+#[test]
+fn test_supports_remote_compaction_for_non_openai_non_azure_provider() {
+    let provider = ModelProviderInfo {
+        name: "Example".into(),
+        base_url: Some("https://example.com/v1".into()),
+        env_key: Some("API_KEY".into()),
+        env_key_instructions: None,
+        experimental_bearer_token: None,
+        auth: None,
+        wire_api: WireApi::Responses,
+        query_params: None,
+        http_headers: None,
+        env_http_headers: None,
+        request_max_retries: None,
+        stream_max_retries: None,
+        stream_idle_timeout_ms: None,
+        websocket_connect_timeout_ms: None,
+        requires_openai_auth: false,
+        supports_websockets: false,
+    };
+
+    assert!(!provider.supports_remote_compaction());
+}
+
 #[test]
 fn test_deserialize_provider_auth_config_defaults() {
     let base_dir = tempdir().unwrap();