Add square text-to-image rendering with a spend gate

Hall of Helix needs a credential-safe render that returns a provenance
receipt and refuses a batch before the quote exceeds its cap. OpenRouter
is the only client; the model and the live budget stay with the founder.

Assistant: grok
Assistant-Session: 01a11ab6-1534-7d63-8606-662b92a80ed6

tests/test_server.py

@@ -2,6 +2,7 @@
 Tests for LLMServer HTTP serve mode (FR-1).
 """
 
+import base64
 import json
 import threading
 import time
@@ -18,6 +19,7 @@ from llm_connect._diagnostics import (
 )
 from llm_connect.adapter import ErrorLLMAdapter, MockLLMAdapter
 from llm_connect.exceptions import LLMAPIError, LLMConfigurationError, LLMTimeoutError
+from llm_connect.images import ImageSpendGate, ImageSpendPolicy
 from llm_connect.models import LLMResponse, RunConfig
 from llm_connect.profiles import CUSTODIAN_TRIAGE_BALANCED, ProfiledLLMAdapter, RuntimeProfile
 from llm_connect.server import LLMServer
@@ -138,6 +140,14 @@ class TestExecute:
         assert status == 400
         assert body == {"error": "invalid JSON body"}
 
+    def test_images_route_is_absent_until_configured(self, server):
+        status, body = _post(
+            f"http://127.0.0.1:{server.port}/images",
+            {"prompt": "a gear"},
+        )
+        assert status == 404
+        assert body == {"error": "not found"}
+
     def test_unknown_post_path_returns_404(self, server):
         status, body = _post(
             f"http://127.0.0.1:{server.port}/wrong",
@@ -411,3 +421,43 @@ class TestExecute:
 
         assert [status for status, _body in results] == [200, 200]
         assert elapsed < 1.5
+
+
+class _ServerImageClient:
+    provider = "openrouter"
+    model = "test/image"
+
+    def generate(self, request):
+        return b"\x89PNG\r\n\x1a\nserver", 0.02
+
+
+def test_images_endpoint_returns_receipt_and_png_bytes():
+    gate = ImageSpendGate(ImageSpendPolicy(max_cost_usd=0.10, quote_usd=0.05))
+    server = LLMServer(
+        adapter=MockLLMAdapter(mock_response="unused"),
+        port=0,
+        image_client=_ServerImageClient(),
+        image_gate=gate,
+    )
+    server.start()
+    try:
+        status, body = _post(
+            f"http://127.0.0.1:{server.port}/images",
+            {"prompt": "a gear", "size": "1024x1024", "output_format": "png"},
+        )
+        execute_status, execute_body = _post(
+            f"http://127.0.0.1:{server.port}/execute",
+            {"prompt": "still here"},
+        )
+    finally:
+        server.stop()
+
+    assert status == 200
+    assert body["receipt"]["provider"] == "openrouter"
+    assert body["receipt"]["model"] == "test/image"
+    assert body["receipt"]["width"] == 1024
+    assert body["receipt"]["within_cap"] is True
+    assert "prompt" not in body["receipt"]
+    assert base64.b64decode(body["image_base64"]).startswith(b"\x89PNG\r\n\x1a\n")
+    assert execute_status == 200
+    assert execute_body["content"] == "unused"