phase2: fix velocity double-scaling in bridge job, bank/program parity, golden RMS test

- render_offline: send velocity as float 0..1 (RenderJob.cpp scales *127);
  old int(0.8*127) was scaled again -> clamp 127, velocity ignored
- forward soundfont_bank/program into bridge job (presence-based, matches
  midi_events_to_messages)
- new tests: bridge branch dispatch (SF_RENDER_ENGINE=bridge -> 404),
  bridge vs pedalboard golden RMS comparison (plan section 6)

tests/test_native_render.py

@@ -44,7 +44,7 @@ def test_bridge_render_sf2_e2e():
         pytest.skip("SF2 fixture missing")
     with tempfile.TemporaryDirectory() as td:
         job = {"instrument_type": 2, "plugin_path": sf2, "sample_rate": 44100, "bpm": 120.0,
-               "notes": [{"pitch": 60, "velocity": 101, "start_beat": 0.0, "duration_beats": 1.0}]}
+               "notes": [{"pitch": 60, "velocity": 0.8, "start_beat": 0.0, "duration_beats": 1.0}]}
         jp = os.path.join(td, "job.json")
         out = os.path.join(td, "out.wav")
         with open(jp, "w", encoding="utf-8") as fh:
@@ -56,3 +56,37 @@ def test_bridge_render_sf2_e2e():
         info = sf.info(out)
         assert info.samplerate == 44100
         assert info.frames == 22050
+
+
+def test_plugins_bridge_branch_dispatch(monkeypatch):
+    """SF_RENDER_ENGINE=bridge: _render_midi_notes_pedalboard phải đi
+    vào native_render (instrument lạ -> 404), không cần pedalboard."""
+    from app.api.v1 import plugins as pl
+    monkeypatch.setattr(pl.settings, "RENDER_ENGINE", "bridge")
+    with pytest.raises(HTTPException) as ei:
+        pl._render_midi_notes_pedalboard("__no_such__", [], bpm=120.0, sample_rate=44100)
+    assert ei.value.status_code == 404
+
+
+def test_bridge_matches_pedalboard_rms():
+    """Golden so sánh (plan §6): bridge vs pedalboard cùng job Nexus → RMS
+    trong tolerance. Skip nếu máy thiếu pedalboard hoặc Nexus VST3."""
+    from app.core.vst_engine import HAS_PEDALBOARD, PluginManager
+    if not HAS_PEDALBOARD:
+        pytest.skip("pedalboard not installed")
+    itype, path = native_render._resolve_instrument("Nexus")
+    if not path:
+        pytest.skip("Nexus VST3 not installed")
+    notes = [{"pitch": 60, "velocity": 0.8, "start_beat": 0.0, "duration_beats": 1.0}]
+    out_b, dur_b = native_render.render_offline("Nexus", notes, bpm=120.0, sample_rate=44100)
+    vst = PluginManager().load_vst("Nexus")
+    if vst is None:
+        pytest.skip("pedalboard cannot load Nexus")
+    ev = [{"note": 60, "start_beat": 0.0, "duration_beats": 1.0, "velocity": 101}]
+    msgs = PluginManager.midi_events_to_messages(ev, 120.0, 44100)
+    buf = vst(msgs, sample_rate=44100, duration=dur_b, num_channels=2)
+    import numpy as np
+    audio = sf.read(out_b)[0]
+    rms_b = float(np.sqrt((audio ** 2).mean()))
+    rms_p = float(np.sqrt((np.asarray(buf.T) ** 2).mean()))
+    assert abs(rms_b - rms_p) < 0.01, f"bridge={rms_b:.5f} pedalboard={rms_p:.5f}"