The shared proxy wrapper in tests/e2e/e2e_gateway.py was misnamed: Gateway is
not a gateway server, it is the client every suite uses to talk to the proxy
(keys, models, chat/embed/ocr, spend read-backs, poll helpers). Rename the
module to proxy_client.py and the class to ProxyClient, with build_gateway
becoming build_proxy_client and the GatewayProvider protocol becoming
ProxyClientProvider. The .gateway attribute suites held is now .proxy. Only
identifiers changed; prose and string literals that use the word gateway for the
proxy-server concept were left alone.
Each suite previously built its own instance through a per-suite build_client()
that called build_gateway() inside, duplicating the proxy wiring across suites.
There is now one session-scoped proxy fixture in tests/e2e/conftest.py; every
suite's client fixture depends on it and injects it, so the wiring lives in one
place. claude_code keeps building its own client directly since it has its own
harness and does not use the shared fixtures.
Behavior is unchanged: shared transport, data-plane/control-plane split routing,
poll budget, typed request/response models, and resource cleanup all go through
the same object.
The e2e docs claimed `e2e`-marked tests skip when no proxy answers the
liveness probe, but the harness has always hard-failed: conftest.py's
pytest_runtest_setup calls pytest.fail, its module docstring states
"hard failures only ... never skip", and logging/conftest.py forbids
skipping outright. Align the docs to the code so the single most
important contract reads the same everywhere; a dead proxy turns a run
red instead of being silently skipped and mistaken for a pass. The
per-suite conftest docstrings that described the shared hook as a
"proxy liveness skip" are corrected to "liveness gate" for the same
reason.
Also scope the no-unit-tests hard rule to what it means: never
substitute a unit test for e2e feature coverage, while explicitly
allowing tests that cover the harness itself (e.g.
coverage_registry/test_collector.py), which carry no e2e marker and
run whether or not a proxy is up.
No product code and no harness logic changed.
Resolves LIT-4554
