fix(check): fall back to tail for empty TAP failure summaries

[YforC]

Why

When a tap-ndjson hook exited non-zero but all parsed records were SKIP or TODO, buildFailureSummary returned an empty string. runHookCompact still emitted failure:, which hid the raw hook output tail and gave agents no useful failure context.

Fixes #86.

What Changed

The hook failure path now only emits failure when buildFailureSummary returns a non-empty summary. Otherwise it falls back to tail, preserving the raw hook output. A regression test covers a non-zero hook whose TAP records are all SKIP/TODO.

Verification

• go test ./internal/check -run ''^(TestBuildFailureSummary|TestRunHookCompactShape_TapNDJSONSkipTodoFallback)$'' -count=1 -v

Full go test ./internal/check -count=1 is blocked on this Windows machine because existing hook tests require sh on PATH.

[friedenberg]

Thanks for this fix — its intent just landed via commit 67e28ef (branch bright-cedar, merging to master shortly), ported rather than merged directly: the FDR 0015 re-platform (merge/check now emit ndjson-crap instead of TAP) rewrote runHookCompactContext into runHookPhase, so the diff here no longer applies. The ported version implements the same fallback — empty failure summary → ring tail — at the new single selection point, which also covers the ndjson-crap format's identical empty-summary case, with regression tests for both formats (TestRunHookPhaseShape_TapNDJSONAllSkipFallsBackToTail / _NdjsonCrapAllSkipFallsBackToTail, modeled on this PR's all-SKIP/TODO repro). #86 will auto-close when the commit reaches master.

This PR can be closed as superseded once that lands — leaving that to you rather than closing someone else's PR.

:clown: Clown 0.4.0+cd38c2d (amarbel-llc/clown@cd38c2d)