sql/logictest: skip remainder of test on snappy infra flake

When the cockroach-go/testserver-based logic tests hit the known
"Can't find decompressor for snappy" infra flake (#124966) during a
mixed-version test, handleWaitForInitErr stops the testserver cluster
and skips the current subtest. However, only the *current* subtest is
skipped; the parent test loop continues and the next subtest (e.g.
post_upgrade) calls into the dead testserver cluster, failing with
"os: process already finished" so that the overall test reports FAIL
instead of SKIP.

Add a sticky skippedDueToSnappy flag to logicTest, set it alongside
the existing ts.Stop() in handleWaitForInitErr, and check it in the
processTestFile subtest loop to break out and mark the parent test
skipped (preserving real failures with a !rootT.Failed() guard). Also
nil out testserverCluster so any stray code path trips the existing
nil guard cleanly.

Resolves: #168412
Epic: none

Release note: None

Author: spilchen

pkg/sql/logictest/logic.go

@@ -1101,6 +1101,13 @@ type logicTest struct {
 	skipOnRetry    bool
 	skippedOnRetry bool
 
+	// skippedDueToSnappy is sticky once set: it indicates that the
+	// "Can't find decompressor for snappy" infra flake was detected
+	// (#124966), the testserver cluster has been stopped, and the
+	// remainder of the test should be skipped rather than run further
+	// directives against the dead cluster.
+	skippedDueToSnappy bool
+
 	// declarativeCorpusCollector used to save declarative schema changer state
 	// to disk.
 	declarativeCorpusCollector *corpus.Collector
@@ -1438,6 +1445,8 @@ func (t *logicTest) handleWaitForInitErr(ts testserver.TestServer, err error) {
 			if ts != nil {
 				ts.Stop()
 			}
+			t.skippedDueToSnappy = true
+			t.testserverCluster = nil
 			t.t().Skip("ignoring init did not finish for node error due to snappy error")
 		}
 	}
@@ -2313,6 +2322,9 @@ func (t *logicTest) processTestFile(path string, config logictestbase.TestCluste
 		if *maxErrs > 0 && t.failures >= *maxErrs {
 			break
 		}
+		if t.skippedDueToSnappy {
+			break
+		}
 		// If subtest has no name, then it is not a subtest, so just run the lines
 		// in the overall test. Note that this can only happen in the first subtest.
 		if len(subtest.name) == 0 {
@@ -2333,6 +2345,10 @@ func (t *logicTest) processTestFile(path string, config logictestbase.TestCluste
 			t.maybeSkipOnRetry(nil)
 		}
 	}
+	if t.skippedDueToSnappy && !t.rootT.Failed() {
+		skip.IgnoreLintf(t.rootT,
+			"skipping remainder of test due to snappy infra flake; see #124966")
+	}
 
 	if (*rewriteResultsInTestfiles || *rewriteSQL) && !t.rootT.Failed() {
 		// Rewrite the test file.