e2e: the dataplane capture leg's outer backstop is silent while the sibling leg reports INCOMPLETE #3657

Summary

In hack/cozytest.sh, the two capture legs handle their outer bound differently. The previous-logs leg records its exit status and reports it: _prev_rc=$? and, on non-zero, "previous-instance capture INCOMPLETE (exit N); kept what landed in ..." (lines 111-124 at 605030b). The dataplane leg three stanzas later is timeout -k 30 600 .../e2e-capture-dataplane.sh ... || true (line 168): if the outer backstop kills the collector, nothing says so, and a truncated dataplane/ directory is indistinguishable from a complete one that found little.

Why it matters

The in-flight bounding work for the dataplane collector makes every read inside it name its own cutoff, which leaves exactly one way for that collector to die silently: the outer backstop at this call site. Closing it makes the collector's honesty contract complete end to end; leaving it open re-creates, one level up, the same "cut short reads as complete" gap the collector-level work removes.

Fix shape

Mirror the sibling leg: capture the exit status instead of || true, and on non-zero print an "INCOMPLETE (exit N); kept what landed" line naming the directory. Two lines, same discipline, same file.