Coordinate foreground search and background inference CPU budgets

apps/desktop/src-tauri/src/settings.rs

@@ -7,7 +7,7 @@ use std::{
     path::{Path, PathBuf},
 };
 
-const SETTINGS_VERSION: u32 = 1;
+const SETTINGS_VERSION: u32 = 2;
 const MAX_SETTINGS_BYTES: u64 = 128 * 1024;
 
 #[derive(Clone, Debug, Deserialize, Serialize, PartialEq, Eq)]
@@ -27,7 +27,7 @@ impl Default for Settings {
         Self {
             version: SETTINGS_VERSION,
             roots: Vec::new(),
-            cpu_threads: 1,
+            cpu_threads: 2,
             model_directory: None,
         }
     }
@@ -71,7 +71,7 @@ pub struct SettingsStore {
 
 impl SettingsStore {
     pub fn load(path: PathBuf) -> Result<Self, String> {
-        let value = match fs::metadata(&path) {
+        let mut value = match fs::metadata(&path) {
             Ok(metadata) => {
                 if metadata.len() > MAX_SETTINGS_BYTES {
                     return Err("Settings file exceeds the size limit.".into());
@@ -82,6 +82,15 @@ impl SettingsStore {
             Err(error) if error.kind() == std::io::ErrorKind::NotFound => Settings::default(),
             Err(error) => return Err(error.to_string()),
         };
+        // Version 1 applied the value independently to both workers. Reserve
+        // one background thread while retaining the old query allocation.
+        if value.version == 1 {
+            if !(1..=8).contains(&value.cpu_threads) {
+                return Err("CPU threads must be between 1 and 8.".into());
+            }
+            value.version = SETTINGS_VERSION;
+            value.cpu_threads = (value.cpu_threads + 1).min(8);
+        }
         let store = Self { path, value };
         store.value.validate()?;
         Ok(store)
@@ -126,7 +135,7 @@ mod tests {
         let directory = tempfile::tempdir().unwrap();
         let path = directory.path().join("settings.json");
         let mut store = SettingsStore::load(path.clone()).unwrap();
-        assert_eq!(store.value.cpu_threads, 1);
+        assert_eq!(store.value.cpu_threads, 2);
         store.add_root(directory.path()).unwrap();
         store.add_root(directory.path()).unwrap();
         let mut next = store.value.clone();
@@ -175,6 +184,8 @@ mod tests {
         fs::write(&path, r#"{"version":1,"roots":[],"cpu_threads":1}"#).unwrap();
         let store = SettingsStore::load(path).unwrap();
         assert!(store.value.model_directory.is_none());
+        assert_eq!(store.value.version, 2);
+        assert_eq!(store.value.cpu_threads, 2);
         let invalid = Settings {
             model_directory: Some(PathBuf::from("relative")),
             ..Settings::default()
@@ -199,3 +210,22 @@ mod tests {
         );
     }
 }
+
+#[cfg(test)]
+mod budget_migration_tests {
+    use super::*;
+    #[test]
+    fn version_two_single_thread_is_explicit_and_invalid_legacy_budget_is_rejected() {
+        let directory = tempfile::tempdir().unwrap();
+        let path = directory.path().join("settings.json");
+        fs::write(&path, r#"{"version":2,"roots":[],"cpu_threads":1}"#).unwrap();
+        assert_eq!(
+            SettingsStore::load(path.clone()).unwrap().value.cpu_threads,
+            1
+        );
+        fs::write(&path, r#"{"version":1,"roots":[],"cpu_threads":9}"#).unwrap();
+        assert!(SettingsStore::load(path.clone()).is_err());
+        fs::write(&path, r#"{"version":1,"roots":[],"cpu_threads":8}"#).unwrap();
+        assert_eq!(SettingsStore::load(path).unwrap().value.cpu_threads, 8);
+    }
+}