Fix Gemini structured output support (#43)

* Fix Gemini structured output by stripping additionalProperties

Gemini's OpenAI-compatible endpoint rejects schemas with
additionalProperties. Strip it from the request body when sending to
generativelanguage.googleapis.com, without affecting cache keys.

Also adds Gemini structured output test and bumps to v0.17.1.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix CI: gate tokio::test behind #[cfg(test)]

tokio macros feature is only available in dev-dependencies,
so the async test needs #[cfg(test)] to avoid compile errors
during cargo check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Mark gemini_structured_output test as #[ignore]

Requires GEMINI_API_KEY which isn't available in CI.
Run with `cargo test -- --ignored` to include it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Gate dotenvy usage behind feature flag in test

CI runs with --no-default-features where dotenvy is unavailable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: anchpop

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "tysm"
-version = "0.17.0"
+version = "0.17.1"
 edition = "2021"
 description = "Batteries-included Rust OpenAI Client"
 license = "MIT"

Cargo.toml

@@ -1262,20 +1262,46 @@ impl ChatClient {
     async fn chat_uncached(&self, chat_request: &ChatRequest) -> Result<String, ChatError> {
         let _permit = self.semaphore.acquire().await.unwrap();
 
-        let response = self
+        let mut request = self
             .http_client
             .post(self.chat_completions_url())
             .header("Authorization", format!("Bearer {}", self.api_key.clone()))
-            .header("Content-Type", "application/json")
-            .json(chat_request)
-            .send()
-            .await?
-            .text()
-            .await?;
+            .header("Content-Type", "application/json");
+
+        // Gemini's OpenAI-compatible endpoint doesn't support additionalProperties
+        // in JSON schemas. We strip it from the request body without affecting the
+        // cache key (which is computed from the original ChatRequest).
+        if self.base_url.host_str() == Some("generativelanguage.googleapis.com") {
+            let mut body = serde_json::to_value(chat_request).unwrap();
+            Self::strip_additional_properties(&mut body);
+            request = request.json(&body);
+        } else {
+            request = request.json(chat_request);
+        }
+
+        let response = request.send().await?.text().await?;
 
         Ok(response)
     }
 
+    /// Recursively remove all `additionalProperties` keys from a JSON value.
+    fn strip_additional_properties(value: &mut serde_json::Value) {
+        match value {
+            serde_json::Value::Object(map) => {
+                map.remove("additionalProperties");
+                for v in map.values_mut() {
+                    Self::strip_additional_properties(v);
+                }
+            }
+            serde_json::Value::Array(arr) => {
+                for v in arr.iter_mut() {
+                    Self::strip_additional_properties(v);
+                }
+            }
+            _ => {}
+        }
+    }
+
     fn decode_json<T: DeserializeOwned>(json: &str) -> Result<T, serde_json::Error> {
         match serde_json::from_str(json) {
             Ok(chat_response) => Ok(chat_response),
@@ -1393,3 +1419,28 @@ fn service_tier_excluded_from_cache_key() {
 
     assert_ne!(request1.cache_key(), request4.cache_key());
 }
+
+#[cfg(test)]
+#[tokio::test]
+#[ignore]
+async fn gemini_structured_output() {
+    use schemars::JsonSchema;
+    use serde::Deserialize;
+
+    #[derive(Deserialize, Debug, JsonSchema)]
+    #[allow(dead_code)]
+    struct CapitalCity {
+        city: String,
+        country: String,
+    }
+
+    #[cfg(feature = "dotenvy")]
+    dotenvy::dotenv().ok();
+    let api_key = std::env::var("GEMINI_API_KEY").expect("GEMINI_API_KEY must be set");
+
+    let client = ChatClient::new(api_key, "gemini-2.5-flash")
+        .with_url("https://generativelanguage.googleapis.com/v1beta/openai/");
+
+    let result: CapitalCity = client.chat("What is the capital of France?").await.unwrap();
+    assert_eq!(result.city, "Paris");
+}

src/chat_completions.rs

@@ -204,6 +204,18 @@ pub(crate) const CHAT_COMPLETIONS: &[ModelCost] = &[
         output: 1.50,
     },
     // GPT-5 models
+    ModelCost {
+        name: "gpt-5.4-pro",
+        input: 30.00,
+        cached_input: None,
+        output: 180.00,
+    },
+    ModelCost {
+        name: "gpt-5.4",
+        input: 2.50,
+        cached_input: Some(0.25),
+        output: 15.00,
+    },
     ModelCost {
         name: "gpt-5.2-chat-latest",
         input: 1.75,