diff --git a/server/src/builder.rs b/server/src/builder.rs
index c88e749..839d30d 100644
--- a/server/src/builder.rs
+++ b/server/src/builder.rs
@@ -45,6 +45,9 @@ pub async fn build_worker(state: AppState) {
             Some(id) => {
                 if let Err(e) = run_build(&state, &id).await {
                     tracing::error!("Build {} failed: {}", id, e);
+                    // Surface the Rust-level error in the deploy log so it's visible in the UI.
+                    let msg = format!("\n[hiy] FATAL: {}\n", e);
+                    let _ = append_log(&state.db, &id, &msg).await;
                     let _ = set_status(&state.db, &id, "failed").await;
                 }
             }
@@ -97,6 +100,24 @@ async fn run_build(state: &AppState, deploy_id: &str) -> anyhow::Result<()> {
 
     let build_dir = format!("{}/builds/{}", state.data_dir, app.id);
 
+    // Log diagnostics before spawning so even a spawn failure leaves a breadcrumb.
+    let cwd = std::env::current_dir()
+        .map(|p| p.display().to_string())
+        .unwrap_or_else(|_| "<unknown>".into());
+    let script_exists = std::path::Path::new(&build_script).exists();
+    append_log(
+        &state.db,
+        deploy_id,
+        &format!(
+            "[hiy] CWD:          {}\n\
+             [hiy] Build script: {} (exists={})\n\
+             [hiy] Build dir:    {}\n\
+             [hiy] Env file:     {}\n---\n",
+            cwd, build_script, script_exists, build_dir, env_file
+        ),
+    )
+    .await?;
+
     let mut child = Command::new("bash")
         .arg(&build_script)
         .env("APP_ID",    &app.id)
@@ -109,7 +130,8 @@ async fn run_build(state: &AppState, deploy_id: &str) -> anyhow::Result<()> {
         .env("BUILD_DIR", &build_dir)
         .stdout(std::process::Stdio::piped())
         .stderr(std::process::Stdio::piped())
-        .spawn()?;
+        .spawn()
+        .map_err(|e| anyhow::anyhow!("Failed to spawn '{}': {}", build_script, e))?;
 
     let stdout = child.stdout.take().expect("piped stdout");
     let stderr = child.stderr.take().expect("piped stderr");