fix: persist LLM config to prefs store so Settings survive restarts

set_llm_config only mutated an in-memory Mutex; lib.rs always started
from LlmConfig::default(). Config now round-trips through the same
dm-pal-prefs.json store as dataDir, with a defaults fallback so a
future shape change can't brick startup. Prefs consts now live in
lib.rs (pub) instead of being mirrored per-module.

src-tauri/src/commands/data_commands.rs

@@ -3,11 +3,8 @@ use serde::{Deserialize, Serialize};
 use std::path::{Path, PathBuf};
 use tauri::Manager;
 use tauri_plugin_store::StoreExt;
-
-// ponytail: the data-dir pref store + key are defined in lib.rs; mirror them
-// here so this module is self-contained for reads/writes.
-const PREFS_STORE: &str = "dm-pal-prefs.json";
-const DATA_DIR_KEY: &str = "dataDir";
+use crate::{DATA_DIR_KEY, PREFS_STORE};
+// PREFS_STORE / DATA_DIR_KEY live in lib.rs (pub) — single source of truth.
 
 #[derive(Debug, Serialize)]
 pub struct DataDirInfo {

src-tauri/src/commands/llm_commands.rs

@@ -3,6 +3,7 @@ use crate::llm::{self, AppState, ChatMessage, ChatResponse, GenerateRequest, Llm
 use serde_json::json;
 use tauri::ipc::Channel;
 use tauri::AppHandle;
+use tauri_plugin_store::StoreExt;
 
 // ─── Simple (non-streaming) generate ─────────────────────────
 
@@ -95,9 +96,18 @@ pub fn get_llm_config(state: tauri::State<'_, AppState>) -> Result<crate::llm::L
 }
 
 #[tauri::command]
-pub fn set_llm_config(state: tauri::State<'_, AppState>, config: crate::llm::LlmConfig) -> Result<(), String> {
-    let mut lock = state.config.lock().map_err(|e| e.to_string())?;
-    *lock = config;
+pub fn set_llm_config(
+    app: AppHandle,
+    state: tauri::State<'_, AppState>,
+    config: crate::llm::LlmConfig,
+) -> Result<(), String> {
+    let stored = serde_json::to_value(&config).map_err(|e| e.to_string())?;
+    *state.config.lock().map_err(|e| e.to_string())? = config;
+    // Persist so Settings survive restart. Same prefs store as dataDir;
+    // load_llm_config in lib.rs falls back to defaults if this ever unparses.
+    let store = app.store(crate::PREFS_STORE).map_err(|e| e.to_string())?;
+    store.set(crate::CONFIG_KEY, stored);
+    store.save().map_err(|e| e.to_string())?;
     Ok(())
 }
 

src-tauri/src/lib.rs

@@ -12,8 +12,11 @@ use tauri_plugin_store::StoreExt;
 // ponytail: the data-dir preference lives in a tiny store at the OS default
 // app_data_dir so it's always discoverable at startup, even before we know the
 // custom location. Key: `dataDir` (absolute path). Empty/missing → default.
-const PREFS_STORE: &str = "dm-pal-prefs.json";
-const DATA_DIR_KEY: &str = "dataDir";
+// The persisted LLM config lives here too (key `llmConfig`) so Settings
+// survive restarts. pub: commands modules read/write through crate::.
+pub const PREFS_STORE: &str = "dm-pal-prefs.json";
+pub const DATA_DIR_KEY: &str = "dataDir";
+pub const CONFIG_KEY: &str = "llmConfig";
 
 /// Resolve the data dir: the configured one if set and usable, else the
 /// default `$APPDATA/dm-toolkit`.
@@ -34,6 +37,15 @@ fn resolve_data_dir(app: &tauri::AppHandle) -> std::path::PathBuf {
     default
 }
 
+/// Load the persisted LLM config (Settings). Falls back to defaults when
+/// missing or unparsable — a future config-shape change never bricks startup;
+/// the DM just re-enters Settings once.
+fn load_llm_config(app: &tauri::AppHandle) -> llm::LlmConfig {
+    let Ok(store) = app.store(PREFS_STORE) else { return llm::LlmConfig::default() };
+    let Some(v) = store.get(CONFIG_KEY) else { return llm::LlmConfig::default() };
+    serde_json::from_value(v).unwrap_or_default()
+}
+
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
     tauri::Builder::default()
@@ -48,7 +60,7 @@ pub fn run() {
             let gen = generations::GenerationStore::open(&data_dir)
                 .expect("open generations db");
             app.manage(AppState {
-                config: Mutex::new(llm::LlmConfig::default()),
+                config: Mutex::new(load_llm_config(&app.handle())),
                 rag,
                 gen,
                 data_dir,