Previously the UC-09 scenario used an allow decision, which exits before
calling queue_event — so saas_unreachable flag had no effect on the test.

Now uses a reject decision (TPM exceeded) which does call queue_event.
Track saas_event_attempts in mock to assert the call was made.
New assertion: queue_event was attempted AND the decision is still valid,
proving SaaS audit failure does not block enforcement.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…truncation

- decision_api.lua: wire llm_limiter.build_error_response in reject path;
  tpm_exceeded/tpd_exceeded/prompt_tokens_exceeded/max_tokens_per_request_exceeded
  now return Content-Type: application/json with OpenAI error structure before ngx.exit(429)
- tests/e2e/test_llm_openai_contract.py: 5 tests verifying 429 body is valid OpenAI
  JSON (error.type=rate_limit_error, error.code=rate_limit_exceeded, message references reason)
  plus Content-Type and RateLimit-* headers still present
- tests/e2e/test_llm_streaming.py: 5 tests verifying mid-stream truncation at
  max_completion_tokens=10 — events 1+2 pass, event 3 triggers truncation,
  response ends with finish_reason=length and [DONE]
- tests/e2e/policy_llm_openai_contract.json: TPM=500, header_hint estimator
- tests/e2e/policy_llm_streaming.json: TPM=100k, defaults.max_completion_tokens=10,
  streaming.buffer_tokens=1, graceful_close mode
- tests/e2e/sse_fixture.txt: 3 SSE events (4+5+6 tokens) + [DONE]
- tests/e2e/mock-streaming-backend.conf: nginx serving sse_fixture.txt as SSE
- docker-compose.test.yml: edge_llm_openai_contract (18089), mock_streaming_backend,
  edge_llm_streaming (18090)
- conftest.py: fixtures for edge_llm_openai_contract_base_url and edge_llm_streaming_base_url

All 497 unit+integration tests continue to pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…on POST

nginx's static file module only handles GET/HEAD — serving sse_fixture.txt
via try_files returned 405 for POST /v1/chat/completions, causing all 5
streaming e2e tests to fail.

Replace mock_streaming_backend with a minimal Python http.server that:
- Accepts POST on any path → returns SSE fixture with correct Content-Type
- Accepts GET / → returns "ok" (used by healthcheck)
- Embeds the SSE content inline (4+5+6 token events for truncation test)

Remove broken mock-streaming-backend.conf and sse_fixture.txt.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

When nginx buffers multiple SSE events into a single body_filter call,
the early return on truncation was discarding events that had already
passed the token budget check and been added to `out`.

Fix: return table_concat(out) .. _build_termination(ctx) so that events
processed before the truncation threshold are forwarded to the client.

For single-event calls (the common streaming case), out is empty so
table_concat({}) = "" — identical behavior to before.

This was caught by the e2e streaming truncation test where the Python
mock sends the complete SSE fixture as a single HTTP response body.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>