flatCallTracer returns wrong result instead of error at timeout

[draganm]

System information

Geth version: geth-1.13.4
CL client & version: lighhouse@lighthouse-5.1.3
OS & Version: Ubuntu 22.04.4 LTS

Expected behaviour

When debug_traceBlockByNumber with flatCallTracer times out, RPC should return an error.

Actual behaviour

Currently debug_traceBlockByNumber with flatCallTracer returns an incorrect trace.

Steps to reproduce the behaviour

• Perform request with very low timeout to force the issue:

{"method":"debug_traceBlockByNumber","params":["0x12cdbd2",{"timeout":"1ms","tracer":"flatCallTracer"}],"id":0,"jsonrpc":"2.0"}

• Perform request with very high timeout to obtain the correct trace:

{"method":"debug_traceBlockByNumber","params":["0x12cdbd2",{"timeout":"20s","tracer":"flatCallTracer"}],"id":0,"jsonrpc":"2.0"}

• compare the outputs

Credit to https://github.com/tsahee for identifying the issue.