feat(agent): SSE — progressive Themen-Tabs (Phase 2)

Der Compliance-Check streamt jetzt progressive Events; der Impressum-Tab
erscheint, sobald das Thema fertig ist, statt am Ende alles auf einmal.
Additiv — das Polling fürs finale Ergebnis bleibt.

- backend: _sse.py (Queue/emit/event_generator) + Endpoint
  /compliance-check/{id}/stream; _update emittiert progress,
  run_agent_outputs emittiert topic (laeuft jetzt frueh nach Phase B),
  Orchestrator emittiert complete/error.
- frontend: SSE-Proxy-Route + EventSource in ComplianceCheckTab merged
  topic-Events in agent_outputs -> Tab erscheint progressiv.
- Tests: backend 5 passed (SSE + agent_outputs); tsc 0 neue Fehler,
  vitest 2 passed, check-loc 0.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-compliance/compliance/tests/test_sse_compliance_check.py

@@ -0,0 +1,50 @@
+"""Phase 2: SSE-Plumbing für den Compliance-Check.
+
+Deckt emit (Queue-Push), _format_sse (SSE-Zeilenformat) und den
+event_generator (hello → Events → stream_close bei 'complete') ab.
+"""
+
+from __future__ import annotations
+
+import asyncio
+
+from compliance.api.agent_check import _sse
+
+
+def test_emit_pushes_and_format():
+    cid = "sse-test-1"
+    _sse.new_queue(cid)
+    _sse.emit(cid, {"type": "topic", "topic": "impressum", "output": {"x": 1}})
+    q = _sse._check_queues[cid]
+    assert q.qsize() == 1
+    ev = q.get_nowait()
+    assert ev["type"] == "topic" and ev["topic"] == "impressum"
+    line = _sse._format_sse(ev)
+    assert line.startswith("data: ") and line.endswith("\n\n")
+    assert '"impressum"' in line
+
+
+def test_emit_is_noop_without_queue():
+    # Kein new_queue → emit darf nicht crashen (best-effort).
+    _sse.emit("does-not-exist-xyz", {"type": "topic"})
+
+
+def test_event_generator_streams_topic_then_closes_on_complete():
+    cid = "sse-test-gen"
+    _sse.new_queue(cid)
+    _sse.emit(cid, {"type": "topic", "topic": "impressum", "output": {}})
+    _sse.emit(cid, {"type": "complete", "status": "completed"})
+
+    async def collect():
+        out = []
+        async for line in _sse.event_generator(cid):
+            out.append(line)
+            if len(out) > 12:  # safety
+                break
+        return out
+
+    blob = "".join(asyncio.run(collect()))
+    assert '"type": "hello"' in blob
+    assert '"topic": "impressum"' in blob
+    assert '"type": "complete"' in blob
+    assert '"type": "stream_close"' in blob