PR-N4: remove SDK conftest stub + finalize no-doubles cleanup

[FluffyAIcode]

Why

Final installment of the no-test-doubles cleanup. Closes the sequence PR-N1 → N2 → N3 → N4. After PR-N4 lands, NO test doubles implementing the verifier / engine / tokenizer protocols remain in the Linux test tree.

What was deleted

File	Δ	What
tests/sdk/python/conftest.py	−203	_start_runtime / _stop_runtime helpers + runtime_address fixture (FakeVerifier-backed)
tests/sdk/python/test_client.py	−157, 13 tests	Client lifecycle against fake runtime
tests/sdk/python/test_session.py	−502, 33 tests	Session.append + .generate + .info + .close end-to-end against fake runtime

Total: ~860 lines, 46 tests deleted.

What was added

File	Lines	Tests	What
tests/integration/test_sdk_real.py	+137	11	Client + Session integration against real Qwen3-0.6B-backed gRPC runtime: lifecycle, error mapping (NOT_FOUND / INVALID_ARGUMENT / SessionClosedError), session info round-trip, close idempotency
tests/integration/conftest.py	+180	—	pytest_collection_modifyitems hook + real_speculative_engine (Qwen3-0.6B SpeculativeEngine, session-scoped) + NEW real_grpc_runtime_address (in-process gRPC server backed by real verifier on background thread, yields host:port)
tests/integration/__init__.py	+0	—	placeholder
scripts/review_pr_n4_on_mac.sh	+93	—	Mac M4 reviewer aid running the full accumulated integration suite

What stays on Linux

tests/sdk/python/test_errors.py (9 tests) — pure _wrap_grpc_error mapping with synthesized grpc.RpcError objects. Verifier-independent; transport-only error-class translation.

CI workflow change

.github/workflows/ci.yaml — dropped kakeya.client, kakeya.session from --include= filter. Linux gate now covers ONLY:

inference_engine/server/{auth, config, errors, grpc_app, metrics, schemas, proto_gen}
inference_engine/memory/*
inference_engine/scheduler/{config, session, pooled_verifier}
inference_engine/pipeline/*
inference_engine/session/store
sdks/python/kakeya/{__init__, errors}
training/repr_align/*

This is the verifier-independent boundary, frozen post PR-N4.

Final state of the no-doubles cleanup

PR	Scope	Tests deleted	Integration test added
#53 PR-N1	FakeVerifier hierarchy	~70	test_coordinator_real.py, test_generator_real.py
#54 PR-N2	DeterministicEngine/Tokenizer (scheduler)	20	test_scheduler_real.py
#55 PR-N3	HTTP shim cluster	88	test_http_shim_real.py, test_engine_real.py, test_tokenizer_real.py, test_streaming_real.py
#56 PR-N4 (this)	SDK conftest stub	46	test_sdk_real.py

After all four merge, tests/integration/ contains:

test_inv3_session_determinism_gate.py          (PR-E1)
test_coordinator_real.py                       (PR-N1)
test_generator_real.py                         (PR-N1)
test_scheduler_real.py                         (PR-N2)
test_http_shim_real.py                         (PR-N3)
test_engine_real.py                            (PR-N3)
test_tokenizer_real.py                         (PR-N3)
test_streaming_real.py                         (PR-N3)
test_sdk_real.py                               (PR-N4)

Linux verification

PYTHONPATH=.:sdks/python coverage run -m pytest <Linux gate paths>:
  649 passed (was 695 on main; -46 net = removed 46 SDK runtime tests).
  100% coverage on 999 stmts (was 1660 on main; -661 net = all
  verifier-dependent modules now integration-only).

Mac M4 evidence (REQUIRED for merge)

bash scripts/review_pr_n4_on_mac.sh runs the full accumulated integration suite (PR-E1 INV-3 + PR-N1 coordinator/generator + PR-N2 scheduler + PR-N3 http_shim/engine/tokenizer/streaming + PR-N4 SDK) against real Qwen3-0.6B and produces pr-n4-mac-integration-tests-<unix>.json evidence.

Stack & merge order note

PR-N4 is branched off main, independent at the file level from PR-N1 (#53), PR-N2 (#54), PR-N3 (#55). However all four PRs add to tests/integration/conftest.py (each contributes a fixture), so post-merge the conftest needs a small reconciliation. Recommended merge order:

1. PR-N1 (adds the marker hook)
2. PR-N2 (adds real_speculative_engine)
3. PR-N3 (uses real_speculative_engine)
4. PR-N4 (this, adds real_grpc_runtime_address)

PR-N4's tests/integration/conftest.py is a superset of N1/N2's; if N4 lands first, the others need to skip their conftest creation and reuse the merged version.