fix: send persona_chat wire shapes in snake_case like file chat

The mobile client dispatches POST /persona_chat/turn with snake_case
keys (persona_id, user_message, num_ctx, ...) per the file-chat
convention, but the persona request/response structs carried camelCase
serde renames (personaId, userMessage, ...), so every dispatch 400'd
with 'missing field personaId'. Drop the renames from
PersonaChatTurnRequest, PersonaChatHistoryView, RenderedPersonaMessage,
and PersonaChatResetRequest — the persona wire shapes now match the
rest of the API (history query, 202 turn_id, SSE skip_before) — and
pin the contract with serialization round-trip tests.

src/ai/persona_chat.rs

@@ -158,38 +158,36 @@ fn is_seed_greeting(content: &str) -> bool {
 }
 
 // ─────────────────────────────────────────────────────────────────────
-// Wire shapes — camelCase out the door.
+// Wire shapes — snake_case, matching the file-chat convention.
 // ─────────────────────────────────────────────────────────────────────
 
 #[derive(Debug, Deserialize)]
 pub struct PersonaChatTurnRequest {
     /// Active persona id. Must match a row in the user's persona store
     /// (built-ins seeded by migration + customs via /personas).
-    #[serde(rename = "personaId")]
     pub persona_id: String,
     /// Free-text user message. Trimmed before validation; empty input is a 400.
-    #[serde(rename = "userMessage")]
     pub user_message: String,
     #[serde(default)]
     pub model: Option<String>,
     #[serde(default)]
     pub backend: Option<String>,
-    #[serde(default, rename = "numCtx")]
+    #[serde(default)]
     pub num_ctx: Option<i32>,
     #[serde(default)]
     pub temperature: Option<f32>,
-    #[serde(default, rename = "topP")]
+    #[serde(default)]
     pub top_p: Option<f32>,
-    #[serde(default, rename = "topK")]
+    #[serde(default)]
     pub top_k: Option<i32>,
-    #[serde(default, rename = "minP")]
+    #[serde(default)]
     pub min_p: Option<f32>,
-    #[serde(default, rename = "enableThinking")]
+    #[serde(default)]
     pub enable_thinking: Option<bool>,
     /// Per-turn system-prompt override. Appended to the persona's prompt
     /// for this turn only; not persisted (persona voice survives a
     /// voice-flipped turn). Empty / whitespace = no override.
-    #[serde(default, rename = "systemPrompt")]
+    #[serde(default)]
     pub system_prompt: Option<String>,
     #[serde(default)]
     pub library: Option<String>,
@@ -200,16 +198,11 @@ pub struct PersonaChatHistoryView {
     /// Rendered transcript — same message shape the file chat's history
     /// endpoint ships, so the client's renderer is shared.
     pub messages: Vec<RenderedPersonaMessage>,
-    #[serde(rename = "turnCount")]
     pub turn_count: u32,
-    #[serde(rename = "modelVersion")]
     pub model_version: String,
     pub backend: String,
-    #[serde(rename = "activeLeafId")]
     pub active_leaf_id: i64,
-    #[serde(rename = "viewingBranchId")]
     pub viewing_branch_id: i64,
-    #[serde(rename = "forkInfo")]
     pub fork_info: Vec<serde_json::Value>,
 }
 
@@ -220,9 +213,8 @@ pub struct PersonaChatHistoryView {
 pub struct RenderedPersonaMessage {
     pub role: String,
     pub content: String,
-    #[serde(rename = "isInitial")]
     pub is_initial: bool,
-    #[serde(rename = "tools", skip_serializing_if = "Vec::is_empty")]
+    #[serde(skip_serializing_if = "Vec::is_empty")]
     pub tools: Vec<crate::ai::handlers::HistoryToolInvocation>,
 }
 
@@ -711,7 +703,6 @@ pub struct PersonaChatHistoryQuery {
 /// one persona.
 #[derive(Debug, Deserialize)]
 pub struct PersonaChatResetRequest {
-    #[serde(rename = "personaId")]
     pub persona_id: String,
 }
 
@@ -1068,4 +1059,64 @@ mod tests {
         // Guard dropped → slot free again.
         assert!(tracker.claim(1, "default", "t7").is_ok());
     }
+
+    #[test]
+    fn persona_chat_turn_request_deserializes_snake_case_wire_body() {
+        // Pins the mobile-client contract: snake_case keys, same as the
+        // file-chat request shapes. A camelCase regression here 400s the
+        // client's dispatch with "missing field persona_id".
+        let body = r#"{
+            "persona_id": "journal",
+            "user_message": "hello",
+            "num_ctx": 4096,
+            "top_p": 0.9,
+            "top_k": 40,
+            "min_p": 0.05,
+            "enable_thinking": true,
+            "system_prompt": "be brief",
+            "library": "main"
+        }"#;
+        let req: PersonaChatTurnRequest = serde_json::from_str(body).unwrap();
+        assert_eq!(req.persona_id, "journal");
+        assert_eq!(req.user_message, "hello");
+        assert_eq!(req.num_ctx, Some(4096));
+        assert_eq!(req.top_p, Some(0.9));
+        assert_eq!(req.top_k, Some(40));
+        assert_eq!(req.min_p, Some(0.05));
+        assert_eq!(req.enable_thinking, Some(true));
+        assert_eq!(req.system_prompt.as_deref(), Some("be brief"));
+        assert_eq!(req.library.as_deref(), Some("main"));
+    }
+
+    #[test]
+    fn persona_chat_history_view_serializes_snake_case_wire_shape() {
+        let view = PersonaChatHistoryView {
+            messages: vec![RenderedPersonaMessage {
+                role: "user".to_string(),
+                content: "hi".to_string(),
+                is_initial: true,
+                tools: Vec::new(),
+            }],
+            turn_count: 1,
+            model_version: "x".to_string(),
+            backend: "local".to_string(),
+            active_leaf_id: 0,
+            viewing_branch_id: 0,
+            fork_info: Vec::new(),
+        };
+        let json = serde_json::to_value(&view).unwrap();
+        // The client's shared ChatHistoryView reads snake_case keys.
+        assert_eq!(json["turn_count"], 1);
+        assert_eq!(json["active_leaf_id"], 0);
+        assert_eq!(json["viewing_branch_id"], 0);
+        assert_eq!(json["messages"][0]["is_initial"], true);
+        assert!(json["messages"][0].get("tools").is_none());
+    }
+
+    #[test]
+    fn persona_chat_reset_request_deserializes_snake_case_wire_body() {
+        let req: PersonaChatResetRequest =
+            serde_json::from_str(r#"{"persona_id": "journal"}"#).unwrap();
+        assert_eq!(req.persona_id, "journal");
+    }
 }