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/section-energy/proposal.md

@@ -0,0 +1,90 @@
+# Proposal: Section Energy Curve
+
+## Intent
+
+All 9 arrangement sections sound identical — full-band at static volume. Professional reggaeton builds energy across sections via sparse-to-dense track layering, velocity variation, and section-level volume riding. This change adds the missing dynamics.
+
+## Scope
+
+### In Scope
+- Centralized `TRACK_ACTIVITY` dict: which track roles play in which sections
+- `build_section_structure()` sets `velocity_mult` and `vol_mult` per section type
+- Unified `_section_active()` helper — single source of truth for section activity
+- All 7 track builders refactored to check centralized activity + apply `velocity_mult`
+- RPPBuilder extended to apply per-clip `vol_mult` (audio items get `D_VOL`, MIDI items get velocity scaling)
+- Rename `build` section to `pre-chorus` (professional reggaeton convention)
+- Update integration tests to match new section behavior
+
+### Out of Scope
+- Volume automation envelopes (REAPER `VOLENV2`) — deferred
+- Transition FX generation (risers, impacts, filtered sweeps)
+- Per-section filter automation (AutoFilter cutoff sweeps)
+- Section scene names in REAPER project — still flat arrangement
+
+## Capabilities
+
+### Modified Capabilities
+- `section-structure`: SectionDef `velocity_mult` and `vol_mult` now populated per section type instead of defaulting to 1.0
+- `track-generation`: All builders consume centralized activity matrix + section multipliers instead of ad-hoc section name checks
+
+### New Capabilities
+- `section-activity`: Centralized activity matrix defining which track roles are active per section type
+- `clip-volume`: ClipDef receives optional `vol_mult` field; RPPBuilder applies it to item `D_VOL` (audio) or velocity scaling (MIDI)
+
+## Approach
+
+**Principle**: Schema fields (`velocity_mult`, `vol_mult`) already exist in `SectionDef`. The bug is they're never populated or consumed. Add the wiring.
+
+1. **Activity matrix** — `TRACK_ACTIVITY` dict in compose.py maps `section_type → {role: bool}`. Section types: `intro`, `verse`, `pre-chorus`, `chorus`, `bridge`, `final`, `outro`.
+
+2. **Section multipliers** — `build_section_structure()` sets `velocity_mult` (controls note velocity) and `vol_mult` (controls clip gain) based on section type:
+   | Section | velocity_mult | vol_mult |
+   |---------|--------------|----------|
+   | intro   | 0.6          | 0.70     |
+   | verse   | 0.7          | 0.85     |
+   | pre-chorus | 0.85      | 0.95     |
+   | chorus  | 1.0          | 1.00     |
+   | bridge  | 0.6          | 0.75     |
+   | final   | 1.0          | 1.00     |
+   | outro   | 0.4          | 0.60     |
+
+3. **Builder refactor** — Replace ad-hoc `if section.name in ("chorus","final")` with `_section_active(section, role, activity)` check. Multiply MIDI velocities by `section.velocity_mult`.
+
+4. **RPPBuilder** — `_build_item()` adds `D_VOL` for audio clips when `clip.vol_mult != 1.0`. MIDI clips already get velocity-scaled notes from step 3.
+
+5. **Section rename** — `build` → `pre-chorus` in `SECTIONS` and all references (`DRUMLOOP_ASSIGNMENTS`, builder filters). Existing section name "build" only appears in compose.py SECTIONS — no external consumers.
+
+## Affected Areas
+
+| Area | Impact | Description |
+|------|--------|-------------|
+| `scripts/compose.py` | Modified | Add `TRACK_ACTIVITY`, `_section_active()`, update `build_section_structure()`, refactor all 7 builders, rename build→pre-chorus |
+| `src/core/schema.py` | Modified | Add `vol_mult` field to `ClipDef` (optional, default 1.0) |
+| `src/reaper_builder/__init__.py` | Modified | `_build_item()` applies `D_VOL` from `clip.vol_mult` |
+| `tests/test_compose_integration.py` | Modified | Update section name references (build→pre-chorus), add activity matrix tests |
+| `tests/test_section_builder.py` | Modified | Add `velocity_mult`/`vol_mult` population tests |
+
+## Risks
+
+| Risk | Likelihood | Mitigation |
+|------|------------|------------|
+| RPP `D_VOL` not recognized by REAPER | Low | REAPER .rpp spec documents D_VOL on ITEM; test with actual REAPER load |
+| Section rename breaks test fixtures | Med | Grep all `.py` for "build" section name; CI catches breakage |
+| Activity matrix too strict — creative users want full band in bridge | Low | Activity matrix is a constant at file top — easy to edit; could be CLI flag later |
+
+## Rollback Plan
+
+Revert commit. No schema migrations needed — `vol_mult` on ClipDef defaults to 1.0 (zero behavioral change if not set). Section rename is cosmetic in output RPP.
+
+## Dependencies
+
+None — no new packages, no external APIs.
+
+## Success Criteria
+
+- [ ] All sections sound audibly different (sparse intro → dense chorus)
+- [ ] Drums + pad only in intro (no bass, no lead, no chords)
+- [ ] Full band in chorus (all 7 tracks active)
+- [ ] Velocity differences between verse (soft) and chorus (hard)
+- [ ] 110 existing tests still pass
+- [ ] `.rpp` output opens in REAPER without errors