address review: fail fast on missing sidecar, bound stderr buffer

Author: slvnlrt

desktop/src-tauri/build.rs

@@ -73,13 +73,26 @@ fn main() {
                 .unwrap_or_else(|_| "x86_64-pc-windows-msvc".to_string());
             let src =
                 std::path::Path::new(&manifest_dir).join(format!("binaries/spacebot-{triple}.exe"));
-            let needs_copy = src.exists()
-                && (!dest.exists()
-                    || src.metadata().and_then(|s| s.modified()).ok()
-                        > dest.metadata().and_then(|d| d.modified()).ok());
+            if !src.exists() {
+                panic!(
+                    "sidecar binary not found at {}. Build the server first \
+                     (`cargo build -p spacebot`) then copy it to binaries/.",
+                    src.display()
+                );
+            }
+
+            let needs_copy = !dest.exists()
+                || src.metadata().and_then(|s| s.modified()).ok()
+                    > dest.metadata().and_then(|d| d.modified()).ok();
             if needs_copy {
                 println!("cargo:warning=Copying sidecar to {}", dest.display());
-                let _ = std::fs::copy(&src, &dest);
+                std::fs::copy(&src, &dest).unwrap_or_else(|error| {
+                    panic!(
+                        "failed to copy sidecar from {} to {}: {error}",
+                        src.display(),
+                        dest.display()
+                    )
+                });
             }
             println!("cargo:rerun-if-changed={}", src.display());
         }

interface/src/components/ConnectionScreen.tsx

@@ -57,7 +57,7 @@ export function ConnectionScreen() {
             if (!sawReady || data.code === null || data.code !== 0) {
               const stderr =
                 stderrLines.length > 0
-                  ? `\n\nstderr:\n${stderrLines.slice(-20).join("\n")}`
+                  ? `\n\nstderr:\n${stderrLines.join("\n")}`
                   : "";
               setSidecarState("error");
               setSidecarError(
@@ -82,6 +82,9 @@ export function ConnectionScreen() {
           onStderr: (line) => {
             console.log("[sidecar stderr]", line);
             stderrLines.push(line);
+            if (stderrLines.length > 20) {
+              stderrLines.splice(0, stderrLines.length - 20);
+            }
           },
         },
       );
@@ -204,7 +207,9 @@ export function ConnectionScreen() {
               )}
 
               {sidecarState === "error" && sidecarError && (
-                <p className="text-xs text-red-400">{sidecarError}</p>
+                <p className="whitespace-pre-wrap text-xs text-red-400">
+                  {sidecarError}
+                </p>
               )}
             </div>
           </>