<!-- GENERATED FROM prd.json — DO NOT EDIT AS AN INDEPENDENT SOURCE. prd.json IS AUTHORITATIVE. -->
# DGR-024: Implement real generated-gRPC protocol harness

- **Status / triage:** completed; `passes: true`
- **Execution mode:** `AFK`
- **Milestone:** `M1`
- **Dependencies:** `DGR-022`, `DGR-023`
- **Blocks (derived):** `DGR-033`, `DGR-042`
- **Labels:** `area:protocol`, `area:testing`, `type:vertical-slice`, `priority:p0`, `ready-for-agent`
- **Evidence class:** `model-free`
- **Hardware:** `none`
- **Model:** `none`
- **Upstream:** `no`

## Objective / description

Build a real generated-gRPC protocol harness around the versioned shard_runtime.proto contract. Use generated Python and C++ stubs over an actual localhost transport and real process lifecycle; exercise captured deterministic protocol vectors and serialized protobuf bytes before a real model worker exists. Do not implement an in-memory fake transport, synthetic model outputs, or a production-looking stub/demo service.

## Acceptance criteria

- [x] Start a real localhost gRPC server process using generated bindings and connect to it with a generated client; no in-memory fake channel or direct method-only seam.
- [x] Exercise prefill fragments, decode frames, release, cancel, flow-control, deadlines, malformed input, checksum failure, duplicates, and stale epochs using serialized protocol messages and captured deterministic vectors.
- [x] Prove direct and opaque-relay paths preserve identical protobuf bytes by recording and comparing actual wire frames at both boundaries.
- [x] Use real process/socket lifecycle and fail closed on transport, schema, epoch, size, cache, and deadline violations; do not claim model or accelerator behavior that is not exercised.
- [x] Applicable shared quality gates pass, and evidence records exact commands, raw outputs, generated artifact identities, wire-frame hashes, changed files, limitations, and dependency handoff.

## Shared quality gates

- Targeted deterministic tests pass; Python changes also pass `python -m compileall packages tests`.
- `git diff --check` passes.
- Default tests are model-download-free, API-credit-free, and GPU-free.
- Evidence README records exact changed files, commands/results, limitations, and dependency handoff; no fabricated evidence or inherited completion credit.
- Native changes pass focused out-of-tree CMake build and CTest; patch changes verify clean apply/check/reverse against the exact llama.cpp pin.
- Runs are opt-in and record exact artifact/split hashes, runtime/upstream pin, backend/driver, hardware, network, commands, and raw metrics. Model artifacts use configured mounted-drive storage and never `/home`.
- Preserve existing Transformers behavior and backend-agnostic Tracker routing/load balancing/billing/relay semantics unless an explicit versioned contract says otherwise. One scoped story commit is expected during execution, but this specification-materialization change is not committed.

## Evidence handoff

Verified evidence: `.scratch/distributed-gguf-runtime/evidence/DGR-024/README.md`. Legacy evidence remains provenance only and grants no implementation completion credit.
