chore: add parse failure logging to E2E event parser (#713)

* chore: use stderr for E2E debug logging to ensure visibility in CI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: add parse failure logging to event parser

Log details when startRun/completeRun/stopRun events fail to parse,
to diagnose CI-only E2E failures.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: FL4TLiN3

e2e/lib/event-parser.ts

@@ -55,7 +55,19 @@ function tryParseEvent(text: string, events: ParsedEvent[]): void {
     if (data.type) {
       events.push({ ...data, raw: text })
     }
-  } catch {}
+  } catch (e) {
+    if (
+      text.includes('"startRun"') ||
+      text.includes('"completeRun"') ||
+      text.includes('"stopRun')
+    ) {
+      process.stderr.write(
+        `[PARSE_FAIL] Failed to parse event (len=${text.length}): ${(e as Error).message}\n`,
+      )
+      process.stderr.write(`[PARSE_FAIL] first 200 chars: ${text.slice(0, 200)}\n`)
+      process.stderr.write(`[PARSE_FAIL] last 200 chars: ${text.slice(-200)}\n`)
+    }
+  }
 }
 
 export function filterEventsByType<T extends RunEvent["type"]>(