diff --git a/src/openhuman/threads/schemas.rs b/src/openhuman/threads/schemas.rs
index 0e64acabb..9af6cf3cb 100644
--- a/src/openhuman/threads/schemas.rs
+++ b/src/openhuman/threads/schemas.rs
@@ -346,6 +346,7 @@ fn to_json<T: serde::Serialize>(outcome: crate::rpc::RpcOutcome<T>) -> Result<Va
 #[cfg(test)]
 mod tests {
     use super::*;
+    use serde_json::json;
 
     const ALL_FUNCTIONS: &[&str] = &[
         "list",
@@ -398,4 +399,175 @@ mod tests {
         assert_eq!(s.function, "unknown");
         assert_eq!(s.namespace, "threads");
     }
+
+    // ── parse::<T>(params) contract ─────────────────────────────────────
+
+    fn obj(value: Value) -> Map<String, Value> {
+        match value {
+            Value::Object(m) => m,
+            _ => panic!("expected JSON object"),
+        }
+    }
+
+    #[test]
+    fn parse_upsert_accepts_snake_case_contract() {
+        let p: UpsertConversationThreadRequest = parse(obj(json!({
+            "id": "t1",
+            "title": "Hello",
+            "created_at": "2026-04-22T00:00:00Z",
+        })))
+        .expect("valid snake_case params parse");
+        assert_eq!(p.id, "t1");
+        assert_eq!(p.title, "Hello");
+        assert_eq!(p.created_at, "2026-04-22T00:00:00Z");
+    }
+
+    #[test]
+    fn parse_upsert_rejects_camel_case_created_at() {
+        // Request params contract is snake_case; camelCase must not silently
+        // succeed because `createdAt` leaves `created_at` missing and also
+        // trips deny_unknown_fields.
+        let err = parse::<UpsertConversationThreadRequest>(obj(json!({
+            "id": "t1",
+            "title": "Hello",
+            "createdAt": "2026-04-22T00:00:00Z",
+        })))
+        .unwrap_err();
+        assert!(err.starts_with("invalid params:"), "prefix: {err}");
+    }
+
+    #[test]
+    fn parse_upsert_rejects_unknown_fields() {
+        let err = parse::<UpsertConversationThreadRequest>(obj(json!({
+            "id": "t1",
+            "title": "Hello",
+            "created_at": "2026-04-22T00:00:00Z",
+            "extra": "nope",
+        })))
+        .unwrap_err();
+        assert!(err.starts_with("invalid params:"), "prefix: {err}");
+        assert!(err.contains("extra"), "field name in error: {err}");
+    }
+
+    #[test]
+    fn parse_upsert_missing_required_field_errors() {
+        let err = parse::<UpsertConversationThreadRequest>(obj(json!({
+            "id": "t1",
+            "title": "Hello",
+        })))
+        .unwrap_err();
+        assert!(err.starts_with("invalid params:"), "prefix: {err}");
+        assert!(err.contains("created_at"), "field name in error: {err}");
+    }
+
+    #[test]
+    fn parse_messages_list_requires_thread_id() {
+        let ok: ConversationMessagesRequest = parse(obj(json!({"thread_id": "t1"}))).unwrap();
+        assert_eq!(ok.thread_id, "t1");
+
+        let err = parse::<ConversationMessagesRequest>(obj(json!({}))).unwrap_err();
+        assert!(err.contains("thread_id"), "err: {err}");
+
+        // camelCase alias is not accepted under deny_unknown_fields.
+        let err = parse::<ConversationMessagesRequest>(obj(json!({"threadId": "t1"}))).unwrap_err();
+        assert!(err.starts_with("invalid params:"), "prefix: {err}");
+    }
+
+    #[test]
+    fn parse_message_append_nested_message_requires_camel_case() {
+        // Outer request is snake_case; nested ConversationMessageRecord is
+        // camelCase by contract (messageType / createdAt). Assert both paths.
+        let ok: AppendConversationMessageRequest = parse(obj(json!({
+            "thread_id": "t1",
+            "message": {
+                "id": "m1",
+                "content": "hi",
+                "type": "text",
+                "sender": "user",
+                "createdAt": "2026-04-22T00:00:00Z",
+            }
+        })))
+        .expect("valid nested camelCase message");
+        assert_eq!(ok.thread_id, "t1");
+        assert_eq!(ok.message.id, "m1");
+        assert_eq!(ok.message.created_at, "2026-04-22T00:00:00Z");
+
+        let err = parse::<AppendConversationMessageRequest>(obj(json!({
+            "thread_id": "t1",
+            "message": {
+                "id": "m1",
+                "content": "hi",
+                "type": "text",
+                "sender": "user",
+                "created_at": "2026-04-22T00:00:00Z",
+            }
+        })))
+        .unwrap_err();
+        assert!(
+            err.contains("createdAt"),
+            "err surfaces expected key: {err}"
+        );
+    }
+
+    #[test]
+    fn parse_generate_title_assistant_message_is_optional() {
+        let without: GenerateConversationThreadTitleRequest =
+            parse(obj(json!({"thread_id": "t1"}))).unwrap();
+        assert_eq!(without.thread_id, "t1");
+        assert_eq!(without.assistant_message, None);
+
+        let with: GenerateConversationThreadTitleRequest = parse(obj(json!({
+            "thread_id": "t1",
+            "assistant_message": "reply",
+        })))
+        .unwrap();
+        assert_eq!(with.assistant_message.as_deref(), Some("reply"));
+    }
+
+    #[test]
+    fn parse_message_update_extra_metadata_optional_and_unknown_rejected() {
+        let without: UpdateConversationMessageRequest = parse(obj(json!({
+            "thread_id": "t1",
+            "message_id": "m1",
+        })))
+        .unwrap();
+        assert!(without.extra_metadata.is_none());
+
+        let with: UpdateConversationMessageRequest = parse(obj(json!({
+            "thread_id": "t1",
+            "message_id": "m1",
+            "extra_metadata": {"k": "v"},
+        })))
+        .unwrap();
+        assert_eq!(with.extra_metadata, Some(json!({"k": "v"})));
+
+        let err = parse::<UpdateConversationMessageRequest>(obj(json!({
+            "thread_id": "t1",
+            "message_id": "m1",
+            "bogus": true,
+        })))
+        .unwrap_err();
+        assert!(err.contains("bogus"), "err: {err}");
+    }
+
+    #[test]
+    fn parse_delete_requires_thread_id_and_deleted_at() {
+        let ok: DeleteConversationThreadRequest = parse(obj(json!({
+            "thread_id": "t1",
+            "deleted_at": "2026-04-22T00:00:00Z",
+        })))
+        .unwrap();
+        assert_eq!(ok.thread_id, "t1");
+
+        let err =
+            parse::<DeleteConversationThreadRequest>(obj(json!({"thread_id": "t1"}))).unwrap_err();
+        assert!(err.contains("deleted_at"), "err: {err}");
+    }
+
+    #[test]
+    fn parse_empty_request_rejects_any_field() {
+        let _: EmptyRequest = parse(obj(json!({}))).unwrap();
+        let err = parse::<EmptyRequest>(obj(json!({"x": 1}))).unwrap_err();
+        assert!(err.starts_with("invalid params:"), "prefix: {err}");
+    }
 }