feat(config): expose paper broker tuning via env (REQ-010 AC-5, BAT-009)

Wire the existing PaperBroker scenario knobs (fill_after_polls /
qty_per_poll / reject_symbols) to daemon env so REQ-011 AC-2 e2e
scenarios (delayed / partial / reject) can be reproduced by a daemon
restart. Unset == prior PaperBroker() behaviour, byte-for-byte (no
regression).

- config.py: PaperBrokerConfig + from_env parsing (TREX_PAPER_*)
- daemon.py: _build_broker injects config.paper into PaperBroker
- .env.example: document the 3 paper tuning keys (paper-only, e2e)
- tests: paper broker defaults + env tuning parsing

SDLC: REQ-010 CHG-20260606-01 (AC-5 added) / -02 (Implemented);
BAT-009 batch-lite release-candidate; REL-001 feedback handoff records
pre-deployment e2e observations incl. event-publisher idle-drop and
paper correlation_id collision (GitHub #4, #5).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/runtime/test_config_dotenv.py

@@ -5,7 +5,11 @@ import pytest
 
 from trex_core.runtime.config import DaemonConfig
 
-_KEYS = ("TREX_POSTGRESQL_DSN", "TREX_TOTAL_SLOTS", "TREX_API_HOST", "TREX_API_PORT")
+_KEYS = (
+    "TREX_POSTGRESQL_DSN", "TREX_TOTAL_SLOTS", "TREX_API_HOST", "TREX_API_PORT",
+    "TREX_PAPER_FILL_AFTER_POLLS", "TREX_PAPER_QTY_PER_POLL",
+    "TREX_PAPER_REJECT_SYMBOLS",
+)
 
 
 @pytest.fixture(autouse=True)
@@ -48,3 +52,26 @@ def test_missing_dsn_raises(tmp_path, monkeypatch):
     monkeypatch.chdir(tmp_path)
     with pytest.raises(RuntimeError):
         DaemonConfig.from_env()
+
+
+def test_paper_broker_defaults(tmp_path, monkeypatch):
+    """Unset paper env == immediate full fills, no rejects (REQ-011)."""
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setenv("TREX_POSTGRESQL_DSN", "dbname=x")
+    cfg = DaemonConfig.from_env()
+    assert cfg.paper.fill_after_polls == 0
+    assert cfg.paper.qty_per_poll is None
+    assert cfg.paper.reject_symbols == frozenset()
+
+
+def test_paper_broker_env_tuning(tmp_path, monkeypatch):
+    """Paper broker scenario knobs are parsed from env (REQ-011)."""
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setenv("TREX_POSTGRESQL_DSN", "dbname=x")
+    monkeypatch.setenv("TREX_PAPER_FILL_AFTER_POLLS", "2")
+    monkeypatch.setenv("TREX_PAPER_QTY_PER_POLL", "4")
+    monkeypatch.setenv("TREX_PAPER_REJECT_SYMBOLS", "005930, 000660 ,")
+    cfg = DaemonConfig.from_env()
+    assert cfg.paper.fill_after_polls == 2
+    assert cfg.paper.qty_per_poll == 4
+    assert cfg.paper.reject_symbols == frozenset({"005930", "000660"})