feat(webapp): show beginning and end of task names in filter dropdown

When task names are too long to fit in the dropdown, truncate in the
middle (showing beginning...end) instead of just cutting off the end.
This helps users identify tasks with colon-namespaced names where the
unique part may be at the end. Show full name in tooltip on hover.

Author: claude

apps/webapp/app/components/primitives/MiddleTruncate.tsx

@@ -0,0 +1,148 @@
+import { useRef, useState, useLayoutEffect, useCallback } from "react";
+import { cn } from "~/utils/cn";
+import { SimpleTooltip } from "./Tooltip";
+
+interface MiddleTruncateProps {
+  text: string;
+  className?: string;
+}
+
+/**
+ * A component that truncates text in the middle, showing the beginning and end.
+ * Shows the full text in a tooltip on hover when truncated.
+ *
+ * Example: "namespace:category:subcategory:task-name" becomes "namespace:cat…task-name"
+ */
+export function MiddleTruncate({ text, className }: MiddleTruncateProps) {
+  const containerRef = useRef<HTMLSpanElement>(null);
+  const measureRef = useRef<HTMLSpanElement>(null);
+  const [displayText, setDisplayText] = useState(text);
+  const [isTruncated, setIsTruncated] = useState(false);
+
+  const calculateTruncation = useCallback(() => {
+    const container = containerRef.current;
+    const measure = measureRef.current;
+    if (!container || !measure) return;
+
+    const parent = container.parentElement;
+    if (!parent) return;
+
+    // Get the available width from the parent container
+    const parentStyle = getComputedStyle(parent);
+    const availableWidth =
+      parent.clientWidth -
+      parseFloat(parentStyle.paddingLeft) -
+      parseFloat(parentStyle.paddingRight);
+
+    // Measure full text width
+    measure.textContent = text;
+    const fullTextWidth = measure.offsetWidth;
+
+    // If text fits, no truncation needed
+    if (fullTextWidth <= availableWidth) {
+      setDisplayText(text);
+      setIsTruncated(false);
+      return;
+    }
+
+    // Text needs truncation - find optimal split
+    const ellipsis = "…";
+    measure.textContent = ellipsis;
+    const ellipsisWidth = measure.offsetWidth;
+
+    const targetWidth = availableWidth - ellipsisWidth - 4; // small buffer
+
+    if (targetWidth <= 0) {
+      setDisplayText(ellipsis);
+      setIsTruncated(true);
+      return;
+    }
+
+    // Binary search for optimal character counts
+    let startChars = 0;
+    let endChars = 0;
+
+    // Alternate adding characters from start and end
+    while (startChars + endChars < text.length) {
+      // Try adding to start
+      const testStart = text.slice(0, startChars + 1);
+      const testEnd = endChars > 0 ? text.slice(-endChars) : "";
+      measure.textContent = testStart + ellipsis + testEnd;
+
+      if (measure.offsetWidth > targetWidth) break;
+      startChars++;
+
+      if (startChars + endChars >= text.length) break;
+
+      // Try adding to end
+      const newTestEnd = text.slice(-(endChars + 1));
+      measure.textContent = text.slice(0, startChars) + ellipsis + newTestEnd;
+
+      if (measure.offsetWidth > targetWidth) break;
+      endChars++;
+    }
+
+    // Ensure minimum characters on each side for readability
+    const minChars = 4;
+    if (startChars < minChars && text.length > minChars * 2 + 1) {
+      startChars = minChars;
+    }
+    if (endChars < minChars && text.length > minChars * 2 + 1) {
+      endChars = minChars;
+    }
+
+    // If combined chars would exceed text length, show full text
+    if (startChars + endChars >= text.length) {
+      setDisplayText(text);
+      setIsTruncated(false);
+      return;
+    }
+
+    const result = text.slice(0, startChars) + ellipsis + text.slice(-endChars);
+    setDisplayText(result);
+    setIsTruncated(true);
+  }, [text]);
+
+  useLayoutEffect(() => {
+    calculateTruncation();
+
+    // Recalculate on resize
+    const resizeObserver = new ResizeObserver(() => {
+      calculateTruncation();
+    });
+
+    const container = containerRef.current;
+    if (container?.parentElement) {
+      resizeObserver.observe(container.parentElement);
+    }
+
+    return () => {
+      resizeObserver.disconnect();
+    };
+  }, [calculateTruncation]);
+
+  const content = (
+    <span ref={containerRef} className={cn("block", className)}>
+      {/* Hidden span for measuring text width */}
+      <span
+        ref={measureRef}
+        className="invisible absolute whitespace-nowrap"
+        aria-hidden="true"
+      />
+      {displayText}
+    </span>
+  );
+
+  if (isTruncated) {
+    return (
+      <SimpleTooltip
+        button={content}
+        content={<span className="max-w-xs break-all font-mono text-xs">{text}</span>}
+        side="top"
+        asChild
+      />
+    );
+  }
+
+  return content;
+}

apps/webapp/app/components/runs/v3/RunFilters.tsx

@@ -31,6 +31,7 @@ import { DateTime } from "~/components/primitives/DateTime";
 import { FormError } from "~/components/primitives/FormError";
 import { Input } from "~/components/primitives/Input";
 import { Label } from "~/components/primitives/Label";
+import { MiddleTruncate } from "~/components/primitives/MiddleTruncate";
 import { Paragraph } from "~/components/primitives/Paragraph";
 import {
   ComboBox,
@@ -654,7 +655,7 @@ function TasksDropdown({
                 <TaskTriggerSourceIcon source={item.triggerSource} className="size-4 flex-none" />
               }
             >
-              {item.slug}
+              <MiddleTruncate text={item.slug} />
             </SelectItem>
           ))}
         </SelectList>