Both fixes are correct and the bug is real.

The break-inside-select footgun was silently swallowing ctx.Done() — classic Go gotcha, canonical fix (extract to a helper that returns). Nice.

Worth noting that this PR also fixes a second, undocumented bug: the original three-way time.After race made the 10 ms case win almost every iteration, so BlockValidation.RetrySleep (default 1s) was effectively being ignored — retries waited ~10 ms instead of the configured duration. The new helper honours the setting properly. Good catch, but worth flagging in the PR body since this changes production retry latency: with ValidationMaxRetries=5, the worst-case retry window grows from ~50 ms to ~5 s. Probably the intended behaviour (the setting docs say "Sleep duration between validation retries"), but ops should know to expect slower failure paths under "missing txmeta" storms. Worth watching prometheusSubtreeValidationValidateSubtreeRetry post-deploy.

Suggestions (non-blocking):

1. Add a test for the actual headline fix — ctx cancellation propagation. The new test verifies the metric and backoff timing, but not that ctx.Done() returns ContextCanceledError instead of being swallowed. A direct unit test on waitForRetryOrPriority would also cheaply cover the priority early-exit path:

   func TestWaitForRetryOrPriority_ContextCancellation(t *testing.T) {
       // ctx canceled mid-wait → returns ContextCanceledError, doesn't block for full retrySleep
   }

2. Error wrapping: errors.NewContextCanceledError("...: %v", subtreeHash, ctx.Err()) formats ctx.Err() into the message string, so errors.Is(err, context.Canceled) won't find it via the wrapped chain — only via the custom error code. If anything upstream relies on errors.Is(err, context.Canceled), it'll miss. Minor — depends on how callers detect cancellation.

3. Minor behaviour drift: if retrySleepDuration <= 0 || isPrioritySubtreeCheckActive(...) now short-circuits with zero wait when priority is already active on entry; the old code waited up to 10 ms first. Almost certainly an improvement, just uncovered by tests.

Strengths to call out:

• Counter delta asserted with Equal(2) not >= — future inflation regressions will fail loudly.
• time.NewTimer/time.NewTicker with defer Stop() plugs the old time.After leak in the retry hot path.