[Bug]: CDC daemon task may panic on CN startup before frontend initialization

[LeftHandCold]

Is there an existing issue for the same bug?

• I have checked the existing issues.

Branch Name

3.0-dev

Commit ID

1b47702

Other Environment Information

- Hardware parameters:
- OS type:
- Others:

Actual Behavior

CN panics during CDC daemon task startup with a nil pointer dereference in frontend internal executor initialization:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4103038]

goroutine 1027 [running]:
github.com/matrixorigin/matrixone/pkg/frontend.getPu(...)
	/go/src/github.com/matrixorigin/matrixone/pkg/frontend/server.go:403
github.com/matrixorigin/matrixone/pkg/frontend.(*internalExecutor).Query(...)
	/go/src/github.com/matrixorigin/matrixone/pkg/frontend/internal_executor.go:172
github.com/matrixorigin/matrixone/pkg/frontend.(*CDCTaskExecutor).retrieveCdcTask(...)
	/go/src/github.com/matrixorigin/matrixone/pkg/frontend/cdc_exector.go:1214
github.com/matrixorigin/matrixone/pkg/frontend.(*CDCTaskExecutor).Start(...)
	/go/src/github.com/matrixorigin/matrixone/pkg/frontend/cdc_exector.go:245

Expected Behavior

CDC daemon tasks should not start until the CN frontend / internal executor dependencies are ready. CN startup should not panic even if HAKeeper delivers CreateTaskService before the frontend stack finishes initialization.

Steps to Reproduce

1. Use branch `3.0-dev`.
2. Ensure there is an existing CDC daemon task that can be claimed when the CN comes up.
3. Start or restart a CN.
4. Let HAKeeper send `CreateTaskService` during early startup.
5. The heartbeat path may create the task service and start the task runner before `initMOServer()` has finished initializing frontend server-level vars and engine dependencies.
6. A claimed CDC task can then call `frontend.NewInternalExecutor(...).Query(...)` and panic in `getPu(service)`.

Additional information

The root cause is a startup ordering race in CN service initialization:

• NewService() calls getHAKeeperClient(), which starts the CN heartbeat task.
• The heartbeat command path can call createTaskService() and startTaskRunner() before initMOServer() completes.
• initMOServer() is what initializes frontend server-level runtime dependencies used by internal executor sessions (setPu, engine, txn client, storage engine, etc.).
• CDC task startup uses an internal executor immediately in retrieveCdcTask(), so starting the runner too early can dereference an uninitialized frontend Pu and crash the CN.

A behavior-safe fix is to allow task service creation early, but defer starting the task runner until CN startup has completed.