fix: make exec_in_container return errors instead of silently warning

- Changed from warn() to error() and return Err()
- Added info logging for each command executed
- Now we can see why downloads/installs fail

PROMPT.md

@@ -5,6 +5,24 @@
 
 ---
 
+## Build Rules - IMPORTANT
+
+**Always use debug builds during development and testing:**
+
+```bash
+# CORRECT - debug build (fast compilation)
+cargo build
+cargo check
+
+# WRONG - do NOT use release builds unless explicitly requested
+# cargo build --release
+```
+
+Debug builds compile much faster and are sufficient for testing functionality.
+Only use `--release` when building final binaries for deployment.
+
+---
+
 ## Weekly Maintenance - EVERY MONDAY
 
 ### Package Review Checklist

src/core/package_manager/facade.rs

@@ -1028,14 +1028,21 @@ Store credentials in Vault:
         Ok(())
     }
     pub fn exec_in_container(&self, container: &str, command: &str) -> Result<()> {
+        info!("Executing in container {}: {}", container, command);
         let output = Command::new("lxc")
             .args(&["exec", container, "--", "bash", "-c", command])
             .output()?;
         if !output.status.success() {
-            warn!(
-                "Container command failed: {}",
-                String::from_utf8_lossy(&output.stderr)
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            let stdout = String::from_utf8_lossy(&output.stdout);
+            error!(
+                "Container command failed.\nCommand: {}\nStderr: {}\nStdout: {}",
+                command, stderr, stdout
             );
+            return Err(anyhow::anyhow!(
+                "Container command failed: {}",
+                if stderr.is_empty() { stdout.to_string() } else { stderr.to_string() }
+            ));
         }
         Ok(())
     }