feat: streaming output for bash commands (#516)

Co-authored-by: Letta <noreply@letta.com>

src/cli/components/CollapsedOutputDisplay.tsx

@@ -0,0 +1,57 @@
+import { Box, Text } from "ink";
+import { memo } from "react";
+
+const COLLAPSED_LINES = 3;
+
+interface CollapsedOutputDisplayProps {
+  output: string; // Full output from completion
+}
+
+/**
+ * Display component for bash output after completion.
+ * Shows first 3 lines with count of hidden lines.
+ * Note: expand/collapse (ctrl+o) is deferred to a future PR.
+ */
+export const CollapsedOutputDisplay = memo(
+  ({ output }: CollapsedOutputDisplayProps) => {
+    // Keep empty lines for accurate display (don't filter them out)
+    const lines = output.split("\n");
+    // Remove trailing empty line from final newline
+    if (lines.length > 0 && lines[lines.length - 1] === "") {
+      lines.pop();
+    }
+
+    if (lines.length === 0) {
+      return null;
+    }
+
+    const visibleLines = lines.slice(0, COLLAPSED_LINES);
+    const hiddenCount = Math.max(0, lines.length - COLLAPSED_LINES);
+
+    return (
+      <Box flexDirection="column">
+        {/* L-bracket on first line - matches ToolCallMessageRich format "  ⎿  " */}
+        <Box>
+          <Text>{"  ⎿  "}</Text>
+          <Text>{visibleLines[0]}</Text>
+        </Box>
+        {/* Remaining visible lines with indent (5 spaces to align with content after bracket) */}
+        {visibleLines.slice(1).map((line, i) => (
+          // biome-ignore lint/suspicious/noArrayIndexKey: Lines are positional output, stable order within render
+          <Text key={i}>
+            {"     "}
+            {line}
+          </Text>
+        ))}
+        {/* Hidden count hint */}
+        {hiddenCount > 0 && (
+          <Text dimColor>
+            {"     "}… +{hiddenCount} lines
+          </Text>
+        )}
+      </Box>
+    );
+  },
+);
+
+CollapsedOutputDisplay.displayName = "CollapsedOutputDisplay";