chore(hardening): tighten security and footprint defaults

crates/llm/src/model_manager.rs

@@ -2,6 +2,7 @@ use std::fmt;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
+use std::sync::{LazyLock, Mutex};
 
 use futures_util::StreamExt;
 use serde::{Deserialize, Serialize};
@@ -158,6 +159,36 @@ const ALL_MODELS: &[LlmModelId] = &[
     LlmModelId::Qwen3_14BQ5,
 ];
 
+static ACTIVE_DOWNLOADS: LazyLock<Mutex<std::collections::HashSet<LlmModelId>>> =
+    LazyLock::new(|| Mutex::new(std::collections::HashSet::new()));
+
+struct DownloadReservation {
+    id: LlmModelId,
+}
+
+impl DownloadReservation {
+    fn acquire(id: LlmModelId) -> Result<Self, DownloadError> {
+        let mut active = ACTIVE_DOWNLOADS
+            .lock()
+            .map_err(|_| DownloadError::Http("download lock poisoned".into()))?;
+        if !active.insert(id) {
+            return Err(DownloadError::Http(format!(
+                "download already in progress for {}",
+                id.as_str()
+            )));
+        }
+        Ok(Self { id })
+    }
+}
+
+impl Drop for DownloadReservation {
+    fn drop(&mut self) {
+        if let Ok(mut active) = ACTIVE_DOWNLOADS.lock() {
+            active.remove(&self.id);
+        }
+    }
+}
+
 pub fn all_models() -> &'static [LlmModelId] {
     ALL_MODELS
 }
@@ -189,20 +220,7 @@ pub fn recommend_tier(total_ram_bytes: u64, total_vram_bytes: Option<u64>) -> Ll
 }
 
 pub fn model_dir() -> PathBuf {
-    if cfg!(target_os = "windows") {
-        std::env::var("LOCALAPPDATA")
-            .map(PathBuf::from)
-            .unwrap_or_else(|_| PathBuf::from("."))
-            .join("kon")
-            .join("models")
-            .join("llm")
-    } else {
-        dirs::home_dir()
-            .unwrap_or_else(|| PathBuf::from("."))
-            .join(".kon")
-            .join("models")
-            .join("llm")
-    }
+    kon_core::paths::app_paths().llm_models_dir()
 }
 
 pub fn model_path(id: LlmModelId) -> PathBuf {
@@ -235,6 +253,7 @@ pub async fn download_model<F>(id: LlmModelId, on_progress: F) -> Result<(), Dow
 where
     F: FnMut(u64, u64) + Send + 'static,
 {
+    let _reservation = DownloadReservation::acquire(id)?;
     let dest = model_path(id);
     tokio::fs::create_dir_all(model_dir()).await?;