fix: DGR-033 repair native worker protocol per cross-review BLOCK

Address the Codex GPT-5.5 review of the standalone fake C++ gRPC Shard
worker. Four root protocol defects fixed:

- Fail closed before SessionOpen: a per-session `opened` flag gates
  chunk/decode so no activation bypasses lifecycle, cancellation, epoch
  or flow-control state (terminal ERROR_CODE_INTERNAL), even when an
  out-of-band Cancel created placeholder state.
- Strict flow-control negotiation: NegotiateFlow takes the strictest of
  peer-vs-worker bounds (mirrors codec.negotiate_flow_control) and the
  negotiated per-session max_chunk_bytes is enforced on every bundle
  instead of trusting the peer proposal.
- In-stream ReleaseSignal now erases session state immediately.
- SessionOpen rejects incompatible schema, fingerprint, and shard-range
  identity and reports the worker's own served fingerprint rather than
  echoing the caller.

Adds 9 regression tests (worker suite 18 -> 27). Real gates on the
rebuilt pinned-gRPC binary: cmake build exit 0; ctest 2/2; worker
pytest 27 passed; harness+protocol 63 passed; compileall 0; diff --check
clean; ldd/nm show 0 llama/ggml linkage. DGR-033 passes -> true.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.scratch/distributed-gguf-runtime/evidence/DGR-033/README.md

@@ -1,6 +1,7 @@
 # DGR-033 evidence — standalone fake C++ gRPC Shard worker
 
-**Completed:** 2026-07-25
+**Completed:** 2026-07-25 (initial); **repaired:** 2026-07-26 after Codex
+GPT-5.5 cross-review BLOCK (see "Cross-review repair" below).
 **Branch:** `ralph/distributed-gguf-opus`
 **Authority:** `.scratch/distributed-gguf-runtime/prd.json`
 **Dependencies:** DGR-022 (lifecycle/status contract), DGR-024 (real generated
@@ -206,3 +207,75 @@ DGR-029/030); the Python client uses that venv's `grpcio==1.82.1`,
   supervision primitives — a readiness line for start detection, `SIGTERM`
   graceful drain with a clean-exit line, and a `--selftest` liveness probe.
   A supervisor can start/monitor/restart the process around these.
+
+## Cross-review repair (2026-07-26)
+
+An independent Codex GPT-5.5 review BLOCKED the initial implementation. Four
+root protocol defects in the native worker were fixed in this worktree
+(`.claude/worktrees/distributed-gguf-opus`); the fake-engine echo semantics and
+supervision shape are unchanged.
+
+### Defects fixed
+
+1. **Activation before SessionOpen bypassed all state.** A chunk/decode whose
+   `route_session_id` had no opened session fell through every `if (state && ...)`
+   guard and was echoed — bypassing lifecycle, cancellation, epoch and
+   flow-control. `SessionState` now carries an `opened` flag set only by a valid
+   `SessionOpen`; chunk and decode fail closed with a terminal
+   `ERROR_CODE_INTERNAL` and end the stream when it is false. A placeholder state
+   created by an out-of-band `Cancel` that races `Open` has `opened == false`, so
+   it can never admit work either.
+2. **Flow control blindly trusted the peer proposal.** `SessionOpen` copied the
+   proposed `credits/max_inflight/max_chunk_bytes` verbatim into session state and
+   the accepted reply. New `ShardRuntimeServiceImpl::NegotiateFlow` takes the
+   strictest bound of peer-vs-worker for every field (mirroring
+   `negotiate_flow_control` in `native_protocol/codec.py`), stores the negotiated
+   ceilings on the session, and enforces the negotiated per-session
+   `max_chunk_bytes` on every bundle (`FakeShardEngine::Validate` now takes the
+   ceiling as an argument instead of a fixed construction-time value).
+3. **In-stream `ReleaseSignal` leaked session state.** The stream `release` arm
+   wrote a terminal status but never dropped the session. It now erases the
+   session under the lock before responding, so KV/credits/dedup are freed
+   immediately (the out-of-band `Release` RPC already erased).
+4. **`SessionOpen` echoed caller identity instead of validating it.** The handshake
+   now rejects an incompatible `schema_version` (`SCHEMA_UNSUPPORTED`), a
+   mismatched model/recipe `Fingerprint` (`FINGERPRINT_MISMATCH`), and a
+   `ShardRange` outside the worker's served range (`SHARD_RANGE_MISMATCH`), each
+   terminal; `SessionAccepted` now reports the worker's own served fingerprint
+   rather than a copy of the caller's.
+
+### Changed files (repair)
+
+- `packages/node/native/worker/shard_service.h` — `opened` +
+  `max_prefill_chunk_tokens` on `SessionState`; `NegotiateFlow` decl; engine now
+  default-constructed.
+- `packages/node/native/worker/shard_service.cpp` — worker-identity constants +
+  fill helpers; `NegotiateFlow`; `SessionOpen` validation/negotiation; fail-closed
+  chunk/decode; per-session `max_chunk_bytes`; in-stream release erase.
+- `packages/node/native/worker/fake_engine.h` — `Validate(bundle, max_chunk_bytes)`.
+- `tests/test_native_shard_worker.py` — extended `_open` (schema/fingerprint/range/
+  flow overrides); fixed `test_release_rpc_is_idempotent` for the new erase
+  semantics; added 9 regression tests (chunk/decode before open, flow-control
+  clamp, negotiated-ceiling cap, in-stream release erase, schema/fingerprint/range
+  rejection, worker-fingerprint-not-caller).
+
+### Re-run gates (real, rebuilt binary)
+
+Build driven through the pinned `cmake` (Unix Makefiles + `gmake`, gRPC 1.82.1):
+
+```text
+cmake --build build/native --parallel 8            -> BUILD_EXIT 0
+ctest --test-dir build/native --output-on-failure  -> 100% (2/2) passed
+  shard_worker_selftest ....... Passed
+  shard_protocol_conformance .. Passed
+python -m pytest -q tests/test_native_shard_worker.py         -> 27 passed
+python -m pytest -q tests/test_shard_runtime_harness.py \
+                    tests/test_native_shard_protocol.py       -> 63 passed
+python -m compileall -q packages tests                       -> exit 0
+git diff --check                                             -> clean
+ldd build/native/shard_worker | grep -iE 'llama|ggml'        -> NONE
+nm -C build/native/shard_worker | grep -cE 'llama_|ggml_'    -> 0
+```
+
+The worker integration suite grew from 18 to 27 tests; all pass against the
+freshly compiled binary. No `.ralph-lane` runtime artifacts were touched.