fix(providers): tolerate null tool_calls in OpenAI-compatible responses

cli/README.md

@@ -35,7 +35,7 @@ The Frontal Code CLI is the primary user interface for interacting with the Fron
 
 - `code-api` for AI provider integration and HTTP services
 - `code-commands` for slash command system and registry
-- `frontal-code-compat-harness` for testing and compatibility validation
+- `code-compat-harness` for testing and compatibility validation
 - `code-runtime` for core functionality and session management
 - `code-plugins` for extensibility and plugin management
 - `code-tools` for tool integration and execution

crates/code-providers/src/providers/openai.rs

@@ -1,6 +1,7 @@
 use std::collections::{BTreeMap, VecDeque};
 use std::time::Duration;
 
+use serde::de::DeserializeOwned;
 use serde::Deserialize;
 use serde_json::{json, Value};
 
@@ -627,10 +628,27 @@ struct ChatMessage {
     role: String,
     #[serde(default)]
     content: Option<String>,
-    #[serde(default)]
+    // Some OpenAI-compatible hosts (e.g. `SGLang`) send `"tool_calls": null`
+    // instead of omitting the field. `#[serde(default)]` only fills missing
+    // keys, so tolerate an explicit null as "no tool calls".
+    #[serde(default, deserialize_with = "deser_null_as_empty_seq")]
     tool_calls: Vec<ResponseToolCall>,
 }
 
+/// Deserialize a sequence, treating an explicit JSON `null` as empty.
+///
+/// Serde's `#[serde(default)]` only substitutes a value for *missing* keys, so
+/// a host that emits `"tool_calls": null` (e.g. `SGLang`) would otherwise fail
+/// with "invalid type: null, expected a sequence".
+fn deser_null_as_empty_seq<'de, D, T>(deserializer: D) -> Result<Vec<T>, D::Error>
+where
+    D: serde::Deserializer<'de>,
+    T: DeserializeOwned,
+{
+    let value = Option::<Vec<T>>::deserialize(deserializer)?;
+    Ok(value.unwrap_or_default())
+}
+
 #[derive(Debug, Deserialize)]
 struct ResponseToolCall {
     id: String,
@@ -673,7 +691,7 @@ struct ChunkChoice {
 struct ChunkDelta {
     #[serde(default)]
     content: Option<String>,
-    #[serde(default)]
+    #[serde(default, deserialize_with = "deser_null_as_empty_seq")]
     tool_calls: Vec<DeltaToolCall>,
 }