Add app-server compaction item notifications tests (#10123)

- add v2 tests covering local + remote auto-compaction item
started/completed notifications

codex-rs/app-server/tests/common/config.rs

@@ -0,0 +1,72 @@
+use codex_core::features::FEATURES;
+use codex_core::features::Feature;
+use std::collections::BTreeMap;
+use std::path::Path;
+
+pub fn write_mock_responses_config_toml(
+    codex_home: &Path,
+    server_uri: &str,
+    feature_flags: &BTreeMap<Feature, bool>,
+    auto_compact_limit: i64,
+    requires_openai_auth: Option<bool>,
+    model_provider_id: &str,
+    compact_prompt: &str,
+) -> std::io::Result<()> {
+    // Phase 1: build the features block for config.toml.
+    let mut features = BTreeMap::from([(Feature::RemoteModels, false)]);
+    for (feature, enabled) in feature_flags {
+        features.insert(*feature, *enabled);
+    }
+    let feature_entries = features
+        .into_iter()
+        .map(|(feature, enabled)| {
+            let key = FEATURES
+                .iter()
+                .find(|spec| spec.id == feature)
+                .map(|spec| spec.key)
+                .unwrap_or_else(|| panic!("missing feature key for {feature:?}"));
+            format!("{key} = {enabled}")
+        })
+        .collect::<Vec<_>>()
+        .join("\n");
+    // Phase 2: build provider-specific config bits.
+    let requires_line = match requires_openai_auth {
+        Some(true) => "requires_openai_auth = true\n".to_string(),
+        Some(false) | None => String::new(),
+    };
+    let provider_block = if model_provider_id == "openai" {
+        String::new()
+    } else {
+        format!(
+            r#"
+[model_providers.mock_provider]
+name = "Mock provider for test"
+base_url = "{server_uri}/v1"
+wire_api = "responses"
+request_max_retries = 0
+stream_max_retries = 0
+{requires_line}
+"#
+        )
+    };
+    // Phase 3: write the final config file.
+    let config_toml = codex_home.join("config.toml");
+    std::fs::write(
+        config_toml,
+        format!(
+            r#"
+model = "mock-model"
+approval_policy = "never"
+sandbox_mode = "read-only"
+compact_prompt = "{compact_prompt}"
+model_auto_compact_token_limit = {auto_compact_limit}
+
+model_provider = "{model_provider_id}"
+
+[features]
+{feature_entries}
+{provider_block}
+"#
+        ),
+    )
+}