Flaky test TestForwardUntilError

panic: test timed out after 10m0s
	running tests:
		TestForwardUntilError (9m52s)
goroutine 6491 [running]:
testing.(*M).startAlarm.func1()
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:2682 +0x359
created by time.goFunc
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/time/sleep.go:215 +0x2d
goroutine 1 [chan receive, 9 minutes]:
testing.(*T).Run(0xc0000b6700, {0x9f7d9f?, 0x0?}, 0xa2b900)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:2005 +0x485
testing.runTests.func1(0xc0000b6700)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:2477 +0x3e
testing.tRunner(0xc0000b6700, 0xc00003fc70)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:1934 +0xea
testing.runTests(0xc000012c48, {0xe823a0, 0x24, 0x24}, {0x7?, 0xc00020dc80?, 0xe8b080?})
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:2475 +0x4b4
testing.(*M).Run(0xc000288280)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:2337 +0x63a
main.main()
	_testmain.go:137 +0x9b
goroutine 6456 [sync.WaitGroup.Wait, 9 minutes]:
sync.runtime_SemacquireWaitGroup(0x8516d0?, 0x50?)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/runtime/sema.go:114 +0x2e
sync.(*WaitGroup).Wait(0xc00033c050)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/sync/waitgroup.go:206 +0x85
github.com/pingcap/tiproxy/pkg/proxy/net.TestForwardUntilError(0xc00011ae00)
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/proxy/net/packetio_test.go:650 +0x1cf
testing.tRunner(0xc00011ae00, 0xa2b900)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:1934 +0xea
created by testing.(*T).Run in goroutine 1
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/testing/testing.go:1997 +0x465
goroutine 6458 [sync.WaitGroup.Wait, 9 minutes]:
sync.runtime_SemacquireWaitGroup(0x8516d0?, 0xa0?)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/runtime/sema.go:114 +0x2e
sync.(*WaitGroup).Wait(0xc00033c0a0)
	/home/prow/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.12.linux-amd64/src/sync/waitgroup.go:206 +0x85
github.com/pingcap/tiproxy/pkg/testkit.TestTCPConnWithListener(0xc00011ae00, 0x424b01?, 0xc00039a078, 0xc00039a090, 0x1)
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/testkit/main.go:72 +0x112
github.com/pingcap/tiproxy/pkg/testkit.TestTCPConn(...)
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/testkit/main.go:36
github.com/pingcap/tiproxy/pkg/proxy/net.testTCPConn(0xc00011ae00, 0xa2bb70, 0xc000388240, 0x1)
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/proxy/net/packetio_test.go:35 +0x112
github.com/pingcap/tiproxy/pkg/proxy/net.TestForwardUntilError.func2()
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/proxy/net/packetio_test.go:636 +0xbc
github.com/pingcap/tiproxy/lib/util/waitgroup.(*WaitGroup).RunWithLogger.func1()
	/home/prow/go/src/github.com/pingcap/tiproxy/lib/util/waitgroup/waitgroup.go:41 +0x53
created by github.com/pingcap/tiproxy/lib/util/waitgroup.(*WaitGroup).RunWithLogger in goroutine 6456
	/home/prow/go/src/github.com/pingcap/tiproxy/lib/util/waitgroup/waitgroup.go:27 +0x90
goroutine 6464 [chan receive, 9 minutes]:
github.com/pingcap/tiproxy/pkg/proxy/net.TestForwardUntilError.func2.2(0xae0cb0?, 0xc0000ce370)
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/proxy/net/packetio_test.go:645 +0xf5
github.com/pingcap/tiproxy/pkg/proxy/net.testTCPConn.func2(0xc00011ae00, {0xae0cb0?, 0xc000124010?})
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/proxy/net/packetio_test.go:43 +0x63
github.com/pingcap/tiproxy/pkg/testkit.TestTCPConnWithListener.func3()
	/home/prow/go/src/github.com/pingcap/tiproxy/pkg/testkit/main.go:67 +0x116
github.com/pingcap/tiproxy/lib/util/waitgroup.(*WaitGroup).RunWithLogger.func1()
	/home/prow/go/src/github.com/pingcap/tiproxy/lib/util/waitgroup/waitgroup.go:41 +0x53
created by github.com/pingcap/tiproxy/lib/util/waitgroup.(*WaitGroup).RunWithLogger in goroutine 6458
	/home/prow/go/src/github.com/pingcap/tiproxy/lib/util/waitgroup/waitgroup.go:27 +0x90

See https://prow.tidb.net/view/gs/prow-tidb-logs/pr-logs/pull/pingcap_tiproxy/1221/pull-unit-test/2099717962410758144

Start with TestForwardUntilError in pkg/proxy/net/packetio_test.go, especially the lines shown in the stack trace, and inspect the related helpers in pkg/testkit/main.go and lib/util/waitgroup/waitgroup.go. Reproduce it with the targeted Go test and repeated runs, then confirm the test completes reliably without the ten-minute timeout.