fix(ci): carry the failing spec's error into the e2e job summary (refs #161)

The per-spec table now has a "Why" column holding the spec's first error,
flattened for a markdown cell: ANSI stripped, newlines collapsed, `|` escaped
(a real report's message is multi-line, coloured, and embeds source-snippet
gutters), clipped to 300 chars. The column only appears when something failed.

So a red e2e names its cause in the summary even when the log is truncated or
the run is killed mid-stream — which is the state #161 was filed from.

Shape verified against an actual @playwright/test 1.61 failing report, not
just the fixture.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

infra/playwright-summary.py

@@ -7,10 +7,34 @@ redirects it into $GITHUB_STEP_SUMMARY. Stdlib only.
 """
 import json
 import os
+import re
 import sys
 
 STATUS_ICON = {"expected": "✅", "unexpected": "❌", "skipped": "⏭️", "flaky": "⚠️"}
 
+# A verdict alone still costs a log dive, and a killed or truncated job leaves no log to dive into
+# (#161) — so a failing spec carries its first error into the table. Playwright errors are multi-line
+# with a "Call log:", which a markdown table cell cannot hold, so they are flattened and clipped.
+ERROR_CLIP = 300
+
+
+def first_error(spec):
+    """The first error message across a spec's test results, flattened for one table cell."""
+    for test in spec.get("tests", []):
+        for result in test.get("results", []):
+            for error in result.get("errors", []):
+                message = (error.get("message") or "").strip()
+                if not message:
+                    continue
+                # Strip ANSI colour, collapse to one line, and keep it inside the cell.
+                message = re.sub(r"\x1b\[[0-9;]*m", "", message)
+                message = " ".join(message.split())
+                if len(message) > ERROR_CLIP:
+                    message = message[:ERROR_CLIP - 1].rstrip() + "…"
+                # `|` would end the cell early.
+                return message.replace("|", "\\|")
+    return ""
+
 
 def walk(suite, out):
     for spec in suite.get("specs", []):
@@ -22,7 +46,8 @@ def walk(suite, out):
                   else "expected" if spec.get("ok", False)
                   else "unexpected")
         out.append({"file": spec.get("file") or suite.get("file") or suite.get("title", ""),
-                    "title": spec.get("title", ""), "status": status})
+                    "title": spec.get("title", ""), "status": status,
+                    "error": first_error(spec) if status in ("unexpected", "flaky") else ""})
     for child in suite.get("suites", []):
         walk(child, out)
 
@@ -46,10 +71,17 @@ def main(path):
     if not specs:
         print("_No specs ran._")
         return 0
-    print("| Spec | Result |")
-    print("| ---- | :----: |")
-    for s in specs:
-        print(f"| {s['file']} › {s['title']} | {STATUS_ICON.get(s['status'], '❔')} |")
+    # The failure column only earns its width when something failed.
+    if any(s["error"] for s in specs):
+        print("| Spec | Result | Why |")
+        print("| ---- | :----: | --- |")
+        for s in specs:
+            print(f"| {s['file']} › {s['title']} | {STATUS_ICON.get(s['status'], '❔')} | {s['error']} |")
+    else:
+        print("| Spec | Result |")
+        print("| ---- | :----: |")
+        for s in specs:
+            print(f"| {s['file']} › {s['title']} | {STATUS_ICON.get(s['status'], '❔')} |")
     return 0