feat: professional reggaeton production engine — 7 SDD changes, 302 tests

- section-energy: track activity matrix + volume/velocity multipliers per section
- smart-chords: ChordEngine with voice leading, inversions, 4 emotion modes
- hook-melody: melody engine with hook/stabs/smooth styles, call-and-response
- mix-calibration: Calibrator module (LUFS volumes, HPF/LPF, stereo, sends, master)
- transitions-fx: FX track with risers/impacts/sweeps at section boundaries
- sidechain: MIDI CC11 bass ducking on kick hits via DrumLoopAnalyzer
- presets-pack: role-aware plugin presets (Serum/Decapitator/Omnisphere per role)

Full SDD pipeline (propose→spec→design→tasks→apply→verify) for all 7 changes.
302/302 tests passing.

.sdd/changes/presets-pack/design.md

@@ -0,0 +1,80 @@
+# Design: presets-pack
+
+## Technical Approach
+
+Restructure `PLUGIN_PRESETS` to `{(plugin, role): chunks}`, add `PresetTransformer` class with per-plugin decoders (Serum=JSON, SoundToys=key=value text, Omnisphere=SynthMaster text), and thread `role` parameter through `make_plugin()` → `_build_plugin()`. No new dependencies — pure Python `base64`, `json`, `re`.
+
+## Architecture Decisions
+
+| Decision | Choice | Rationale |
+|----------|--------|-----------|
+| Data structure | `dict[tuple[str,str], list[str]]` — `{(plugin, role): chunks}` | Avoids dict-of-dicts nesting; simpler iteration in tests |
+| Transformation | Separate `PresetTransformer` class per plugin format | Serum/JSON, SoundToys/text, Omnisphere/text are different parsers; isolation = testability |
+| Role threading | Optional `role` param on `make_plugin()` and `_build_plugin()` | Zero breaking changes; None = current behavior |
+| Fallback chain | role → default → None | Backward compatible; existing tests don't break |
+
+## Data Flow
+
+```
+compose.py: make_plugin("Serum_2", 0, role="bass")
+  → _resolve_preset("Serum_2", "bass")
+    → PLUGIN_PRESETS[("Serum_2", "bass")]  ← PresetTransformer output
+  → PluginDef(preset_data=bass_chunks)
+
+reaper_builder: _build_plugin(plugin)
+  → entry = PLUGIN_REGISTRY.get(resolved_name)
+  → preset_data = PLUGIN_PRESETS.get((resolved_name, plugin.role))
+                  or PLUGIN_PRESETS.get((resolved_name, "default"))
+  → _build_plugin_element(display, file, uid, preset_data)
+```
+
+## File Changes
+
+| File | Action | Description |
+|------|--------|-------------|
+| `src/reaper_builder/__init__.py` | Modify | Restructure `PLUGIN_PRESETS` to `{(k,role): chunks}`; `_build_plugin()` reads `plugin.role` for lookup |
+| `src/reaper_builder/preset_transformer.py` | Create | `PresetTransformer` class with `decode()`, `transform(role)`, `encode()`; per-plugin transformers |
+| `src/composer/templates.py` | Modify | `_parse_vst_block()` and `_make_plugin_template()` handle new `PLUGIN_PRESETS` structure |
+| `scripts/compose.py` | Modify | `make_plugin()` accepts `role` param, threads from `FX_CHAINS` key |
+| `src/core/schema.py` | Modify | `PluginDef` gets optional `role: str \| None = None` field |
+| `tests/test_preset_transform.py` | Create | Round-trip tests for 3 plugins × N roles |
+
+## PresetTransformer Design
+
+```python
+class PresetTransformer:
+    TRANSFORMERS: dict[str, Callable] = {
+        "Serum_2": _transform_serum,
+        "Decapitator": _transform_decapitator,
+        "Omnisphere": _transform_omnisphere,
+    }
+
+    @staticmethod
+    def derive(plugin: str, default_chunks: list[str], role: str) -> list[str]:
+        transformer = PresetTransformer.TRANSFORMERS.get(plugin)
+        if not transformer:
+            return default_chunks  # no transform = use default unchanged
+        return transformer(default_chunks, role)
+```
+
+Per-transformer functions:
+- `_transform_serum(chunks, role)` — decode JSON body, modify `processor.osc.type`, `processor.filter.cutoff`, `processor.fx`
+- `_transform_decapitator(chunks, role)` — decode text body, modify `Drive`, `Tone`, `Style` lines
+- `_transform_omnisphere(chunks, role)` — decode SynthMaster body, modify `Atk`, `Dec`, `Filter Freq` lines
+
+## Testing Strategy
+
+| Layer | What | Approach |
+|-------|------|----------|
+| Unit | PresetTransformer per plugin | decode → modify → encode for each (plugin, role); verify JSON/keys changed |
+| Integration | make_plugin + _build_plugin with role | Build PluginDef, verify preset_data differs per role |
+| Regression | `test_make_plugin_known_key` | Existing tests pass unchanged (role=None fallback) |
+| Round-trip | encode(decode(chunks)) == chunks | Each plugin × role; verify chunk count, base64 charset, structure integrity |
+
+## Migration / Rollout
+
+No migration required. `PluginDef.role` defaults to None. Existing callers that don't pass role continue working with `"default"` preset. Revert: flatten `PLUGIN_PRESETS` back to single-level dict, remove `role` param.
+
+## Open Questions
+
+None.