TiFlash panic if an Region across multiple table_id or index keyrange

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Generate a Region that across multiple table_id or index keyrange. With

{"id":1560448274,"start_key":"7480000000002874FF3E00000000000000F8","end_key":"7480000000002874FFA55F698000000000FF0000010400000000FF0009EEB500000000FB"}

2. Manually add a Region learner peer to tiflash using pd-ctl

pd-ctl -u 127.0.0.1:2379 operator add add-learner 1560448274 36

2. What did you expect to see? (Required)

3. What did you see instead (Required)

tiflash panic

[2026/06/22 13:12:06.248 +00:00] [FATAL] [Exception.cpp:96] ["Code: 49, e.displayText() = DB::Exception: Illegal region range, should not happen, start_key=? end_key=?, e.what() = DB::Exception, Stack trace:
  0xaaaae5344cc4    DB::Exception::Exception<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>(int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>&&) [tiflash+79252676]
  0xaaaae8ff9e78    DB::RegionRangeKeys::RegionRangeKeys(DB::StringObject<true>&&, DB::StringObject<true>&&) [tiflash+142909048]
                    dbms/src/Storages/KVStore/MultiRaft/RegionState.cpp:149
  0xaaaae8ff9310    DB::RegionState::updateRegionRange() [tiflash+142906128]
                    /usr/local/bin/../include/c++/v1/__memory/construct_at.h:41
  0xaaaae8fe8878    DB::RegionMeta::RegionMeta(metapb::Peer, metapb::Region, raft_serverpb::RaftApplyState) [tiflash+142837880]
                    dbms/src/Storages/KVStore/MultiRaft/RegionMeta.cpp:495
  0xaaaae8f24e98    DB::KVStore::genRegionPtr(metapb::Region&&, unsigned long, unsigned long, unsigned long) [tiflash+142036632]
                    dbms/src/Storages/KVStore/KVStore.cpp:495
  0xaaaae8f76338    PreHandleSnapshot [tiflash+142369592]
                    dbms/src/Storages/KVStore/FFI/ProxyFFI.cpp:685
  0xffff8cf5eb64    proxy_ffi::engine_store_helper_impls::_$LT$impl$u20$proxy_ffi..interfaces..root..DB..EngineStoreServerHelper$GT$::pre_handle_snapshot::hf1ec63b2511a1357 [libtiflash_proxy.so+63744868]
                    contrib/tiflash-proxy/proxy_components/proxy_ffi/src/engine_store_helper_impls.rs:292
  0xffff8ca7c978    engine_store_ffi::core::forward_raft::snapshot::pre_handle_snapshot_impl::hf91bcd6c2b69826b [libtiflash_proxy.so+58624376]
                    contrib/tiflash-proxy/proxy_components/engine_store_ffi/src/core/forward_raft/snapshot.rs:97
  0xffff8d81eaa4    yatp::task::future::RawTask$LT$F$GT$::poll::h2879d332e78fab98 [libtiflash_proxy.so+72919716]
                    /workspace/.cargo/git/checkouts/yatp-e704b73c3ee279b6/793be4d/src/task/future.rs:59
  0xffff8f21b6d8    _$LT$yatp..task..future..Runner$u20$as$u20$yatp..pool..runner..Runner$GT$::handle::h5569b38cc95e4640 [libtiflash_proxy.so+100169432]
                    /workspace/.cargo/git/checkouts/yatp-e704b73c3ee279b6/793be4d/src/task/future.rs:387
  0xffff8f20b010    std::sys_common::backtrace::__rust_begin_short_backtrace::h9b780a3f40586e98 [libtiflash_proxy.so+100102160]
                    /root/.rustup/toolchains/nightly-2023-12-28-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:155
  0xffff8f20cec4    core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::hd3739b609fe7651a [libtiflash_proxy.so+100110020]
                    /root/.rustup/toolchains/nightly-2023-12-28-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250
  0xffff8e864d18    std::sys::unix::thread::Thread::new::thread_start::h35e031273648d290 [libtiflash_proxy.so+89984280]
                    /root/.rustup/toolchains/nightly-2023-12-28-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/unix/thread.rs:108
  0xffff88f4ab40    start_thread [libc.so.6+527168]
  0xffff88fb515c    thread_start [libc.so.6+962908]"] [source="RawCppPtr DB::PreHandleSnapshot(EngineStoreServerWrap *, BaseBuffView, uint64_t, SSTViewVec, uint64_t, uint64_t)"] [thread_id=4581]

4. What is your TiFlash version? (Required)

v8.5.4

Reproduce the failure by creating the Region described and adding a learner with pd-ctl. Start at dbms/src/Storages/KVStore/MultiRaft/RegionState.cpp:149 and follow the snapshot path through RegionMeta.cpp:495, KVStore.cpp:495, ProxyFFI.cpp:685, and the Rust snapshot entry point. Done means a Region spanning multiple table_id or index keyranges no longer causes TiFlash to panic.