External debuggers for interpreter-hosted programs often rely on ad hoc integration points that are hard to evolve and validate across versions. This paper presents DDF-DBG, a compact debugger protocol that uses exported in-process protocol blocks and ptrace memory access instead of sockets or custom runtime agents. The current protocol revision separates lifecycle, request, and event ownership into three ABI-stable blocks, and adds capability negotiation so optional features can be enabled without breaking core run-control semantics. The protocol defines typed commands and events, sequence-based synchronization, request/response slots for breakpoint and value-inspection operations, and compatibility checks over protocol and ABI metadata. We also define a compact debug-data interface (DDF) consumed by the debugger to resolve source locations, source breakpoints, and structured variable metadata. A prototype integration is currently implemented end to end in a debugger and one interpreter runtime, and initial usage indicates that protocol-level separation improves interoperability and keeps implementation complexity manageable. We report current limitations and planned evaluation work on overhead, robustness, and protocol evolution.