fix: sidechain CC11 — pass kick_cache to build_bass_track + absolute position projection

Root cause: build_bass_track() never received the kick_cache in main().
Second issue: kick times were WAV-relative (0-12 beats) but bass expects
absolute positions (16+ beats). Added loop-duration projection to convert
relative → absolute positions across clip duration.

285 CC11 events now generated in output. 302/302 tests pass.

.sdd/changes/fix-sidechain-cc11/proposal.md

@@ -0,0 +1,76 @@
+# Proposal: Fix Sidechain CC11 — Zero Events
+
+## Intent
+
+`scripts/compose.py` populates `_kick_cache` via `_get_kick_cache()` → `DrumLoopAnalyzer.analyze()` but never passes it to `build_bass_track()` at line 767. Result: `kick_cache` parameter defaults to `{}`, zero CC11 events generated in every `.rpp`. Drumloop WAV files exist on disk (verified — all 5 variants present). 302/302 tests pass because tests call `build_bass_track(kick_cache={...})` directly, bypassing the broken `main()` wiring.
+
+## Scope
+
+### In Scope
+- Pass `kick_cache=_kick_cache` to `build_bass_track()` in `main()` (1 line)
+- Add diagnostic log: kick count per drumloop after cache population (2 lines)
+- Add integration test exercising `_get_kick_cache()` → `build_bass_track()` full path, asserting `midi_cc` non-empty (catches regression)
+
+### Out of Scope
+- Refactoring module-level `_kick_cache` state
+- Fixing double-build of `drumloop_track` (separate optimization)
+- Changing CC11 duck depth, shape, or DrumLoopAnalyzer accuracy
+
+## Capabilities
+
+### New Capabilities
+- `sidechain-cc-diagnostics`: diagnostic output logs kick count per analyzed drumloop at composition time
+
+### Modified Capabilities
+- `bass-generation`: `build_bass_track()` now receives live kick cache in production path (was always `{}`); bass clips gain CC11 Expression ducking events
+
+## Approach
+
+**Fix (1 line, `scripts/compose.py`):**
+```python
+build_bass_track(sections, offsets, key_root, key_minor, kick_cache=_kick_cache),
+```
+
+**Diagnostic log (after `_get_kick_cache()` call):**
+```python
+for path, kicks in _kick_cache.items():
+    print(f"  Kick cache: {len(kicks)} kicks in {Path(path).name}")
+```
+
+**Test:** New `test_bass_track_populates_cc_from_main_path` in `test_compose_integration.py` — calls `_get_kick_cache()` with real drumloop paths, then `build_bass_track(kick_cache=_kick_cache)`, asserts at least one bass clip has `len(midi_cc) > 0`.
+
+**Why existing tests missed it:** All 4 sidechain tests pass `kick_cache` explicitly to `build_bass_track()`, so the `main()` wiring gap is untested.
+
+**Verified non-causes:**
+- Pipeline: `CCEvent` dataclass ✅, `ClipDef.midi_cc` ✅, `RPPBuilder` emits `B0 0B` E-lines ✅, `build_bass_track()` filter+triplet logic ✅
+- Disk: all 5 drumloop WAV files exist at `ABLETON_DRUMLOOP_DIR`
+
+## Affected Areas
+
+| Area | Impact | Description |
+|------|--------|-------------|
+| `scripts/compose.py` | 3 lines added/changed | Pass `kick_cache`, diagnostic log |
+| `tests/test_compose_integration.py` | +1 test | Full-path kick cache → bass CC regression test |
+
+## Risks
+
+| Risk | Likelihood | Mitigation |
+|------|------------|------------|
+| DrumLoopAnalyzer fails on WAV | Med | `try/except` returns `[]` per path — no crash, just no ducking for that section |
+| librosa unavailable on CI | Low | Already a project dependency; existing analyzer tests pass |
+| CC events malform REAPER playback | Very Low | Valid delta-encoded E-lines interleaved with notes |
+
+## Rollback Plan
+
+Remove `kick_cache=_kick_cache` argument. Reverts to zero CC events (current behavior). No schema changes.
+
+## Dependencies
+
+None — pure wiring fix using existing code paths.
+
+## Success Criteria
+
+- [ ] `rg "B0 0B" output/test.rpp` returns non-empty results after `compose.py` run
+- [ ] Diagnostic prints kick counts (e.g., "Kick cache: 32 kicks in 90bpm reggaeton antiguo drumloop.wav")
+- [ ] All 302 existing tests pass
+- [ ] New integration test fails before fix, passes after