Move the landed filter-voice-path track from PLAN.md into COMPLETED.md with full narrative (quantizer removal, editor floor raise). Mark Θ-W2 fully landed, matching W1's phrasing; fix a stale forward reference.
Two Greek-lettered phases (Θ instrument overhaul, Ξ resample loop): sequenced waves, parallel tracks on disjoint surfaces, per-track acceptance criteria, carried-forward open questions, traceability table. TODO-1.0.md retained as verbatim-provenance appendix.