auto-git:

[change] src/app/App.tsx
 [change] src/app/app.css

src/app/App.tsx

@@ -91,7 +91,11 @@ function formatDiagnosticCount(count: number, label: string): string {
   return `${count} ${label}${count === 1 ? "" : "s"}`;
 }
 
-function getViewportCaption(toolMode: "select" | "box-create", brushCount: number): string {
+function getViewportCaption(toolMode: "select" | "box-create" | "play", brushCount: number): string {
+  if (toolMode === "play") {
+    return "Runner is active.";
+  }
+
   if (toolMode === "box-create") {
     return `Box Create is active. Move over the grid to preview snapped placement, then click to place a ${DEFAULT_BOX_BRUSH_SIZE.x} x ${DEFAULT_BOX_BRUSH_SIZE.y} x ${DEFAULT_BOX_BRUSH_SIZE.z} box.`;
   }
@@ -1586,7 +1590,7 @@ export function App({ store, initialStatusMessage }: AppProps) {
 
             {primaryPlayerStart === null ? (
               <ul className="placeholder-list">
-                <li>No Player Start is authored yet. First-person can still fall back, but Orbit Visitor is the safer default.</li>
+                <li>No Player Start is authored yet. Orbit Visitor can still run, but first-person run is blocked until you place one.</li>
               </ul>
             ) : (
               <div className="stat-card">
@@ -1622,7 +1626,11 @@ export function App({ store, initialStatusMessage }: AppProps) {
             </div>
 
             <div className="inline-actions">
-              <button className="toolbar__button toolbar__button--accent" type="button" onClick={handleEnterPlayMode}>
+              <button
+                className={`toolbar__button toolbar__button--accent ${blockingDiagnostics.length > 0 ? "toolbar__button--warn" : ""}`}
+                type="button"
+                onClick={handleEnterPlayMode}
+              >
                 Enter Run Mode
               </button>
             </div>
@@ -1641,7 +1649,10 @@ export function App({ store, initialStatusMessage }: AppProps) {
           <span className="status-bar__strong">Status:</span> {statusMessage}
         </div>
         <div>
-          <span className="status-bar__strong">History:</span> {editorState.lastCommandLabel ?? "No commands yet"}
+          <span className="status-bar__strong">Diagnostics:</span>{" "}
+          {diagnostics.length === 0
+            ? "Ready"
+            : `${formatDiagnosticCount(blockingDiagnostics.length, "error")}, ${formatDiagnosticCount(warningDiagnostics.length, "warning")}`}
         </div>
       </footer>
 

src/app/app.css

@@ -137,6 +137,10 @@ button:disabled {
   font-weight: 700;
 }
 
+.toolbar__button--warn {
+  box-shadow: inset 0 0 0 1px rgba(255, 241, 213, 0.28);
+}
+
 .workspace {
   display: grid;
   grid-template-columns: minmax(240px, 280px) minmax(0, 1fr) minmax(280px, 320px);
@@ -234,6 +238,14 @@ button:disabled {
   flex-wrap: wrap;
 }
 
+.info-banner {
+  padding: 12px 14px;
+  color: var(--color-text);
+  background: rgba(137, 182, 255, 0.09);
+  border: 1px solid rgba(137, 182, 255, 0.24);
+  border-radius: 12px;
+}
+
 .form-section {
   display: flex;
   flex-direction: column;
@@ -404,6 +416,68 @@ button:disabled {
   font-size: 0.82rem;
 }
 
+.diagnostic-list {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.diagnostic-item {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  padding: 12px 14px;
+  border-radius: 14px;
+  border: 1px solid rgba(255, 255, 255, 0.09);
+  background: rgba(255, 255, 255, 0.03);
+}
+
+.diagnostic-item--error {
+  border-color: rgba(207, 123, 66, 0.45);
+  background: rgba(207, 123, 66, 0.09);
+}
+
+.diagnostic-item--warning {
+  border-color: rgba(243, 190, 143, 0.36);
+  background: rgba(243, 190, 143, 0.08);
+}
+
+.diagnostic-item__header {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.diagnostic-badge {
+  padding: 0.2rem 0.55rem;
+  border-radius: 999px;
+  font-size: 0.7rem;
+  font-weight: 700;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+.diagnostic-badge--error {
+  color: #20140c;
+  background: #cf7b42;
+}
+
+.diagnostic-badge--warning {
+  color: #20140c;
+  background: #f3be8f;
+}
+
+.diagnostic-item__scope,
+.diagnostic-item__path {
+  color: var(--color-muted);
+  font-size: 0.76rem;
+}
+
+.diagnostic-item__message {
+  font-size: 0.9rem;
+  line-height: 1.45;
+}
+
 .viewport-region {
   display: grid;
   grid-template-rows: 42px minmax(0, 1fr);
@@ -459,6 +533,10 @@ button:disabled {
   cursor: crosshair;
 }
 
+.viewport-canvas--box-create {
+  cursor: copy;
+}
+
 .runner-canvas {
   flex: 1 1 auto;
   cursor: grab;
@@ -471,6 +549,38 @@ button:disabled {
   height: 100%;
 }
 
+.viewport-canvas__overlay {
+  position: absolute;
+  top: 18px;
+  left: 18px;
+  z-index: 1;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  max-width: min(380px, calc(100% - 36px));
+  padding: 12px 14px;
+  color: #f3e8da;
+  background: rgba(8, 10, 14, 0.58);
+  border: 1px solid rgba(255, 255, 255, 0.12);
+  border-radius: 14px;
+  backdrop-filter: blur(10px);
+  pointer-events: none;
+}
+
+.viewport-canvas__overlay-badge {
+  color: var(--color-accent-strong);
+  font-size: 0.72rem;
+  font-weight: 700;
+  letter-spacing: 0.14em;
+  text-transform: uppercase;
+}
+
+.viewport-canvas__overlay-text,
+.viewport-canvas__overlay-preview {
+  font-size: 0.82rem;
+  line-height: 1.45;
+}
+
 .viewport-canvas__fallback,
 .runner-canvas__fallback {
   position: absolute;