<!-- SPDX-License-Identifier: CC-BY-4.0 -->
# Decision Record

## Decisions

- Readiness is `L2 V5 build-packet candidate`.
- The instrument is treated as a struck steel-bar idiophone with a keyboard
  action, not as a string piano variant.
- The first risks are hammer rebound, bar support, resonator matching, damper
  control, and action regulation.
- The packet intentionally avoids pitch ranges, bar dimensions, resonator
  dimensions, hammer weights, action ratios, and CAD/DXF outputs.
- L2 scope is limited to naming coupon classes, review gates, authority
  boundaries, and measurement logs.
- Visual-output register rows may be `concept_only` or `pending_measurement`;
  no artifact is fabrication authority.
- The first promotion artifact should be a single-bar coupon plus key-action
  mule, not a full keyboard or full pitch set.

## L2 Promotion Gates

- Bar coupon proves sustain, decay, support sensitivity, tuning response, and
  repeatable strike behavior.
- Hammer comparison records rebound, tone, wear, and contact behavior.
- Key-action mule records key feel, hammer travel, checking, damper timing,
  regulation access, and mechanical noise.
- Resonator comparison records loudness, color, sustain, and coupling without
  claiming tuned volumes.
- Damper test records clean stop behavior and release noise.
- CAD, DXF, and drawings remain blocked until measured or reviewed parameters
  exist.

## Open Questions

- What bar material and heat treatment should a first coupon use?
- How should bars be supported so they speak freely but stay stable under felt
  hammer strikes?
- What hammer felt and contact shape gives a clear attack without harshness?
- Should resonator tests begin with individual boxes or a shared resonator
  rail?
- How should dampers lift and return without adding release noise?
- What keyboard action can be regulated simply in a prototype shop setting?
- Which measurements should be captured before deciding on any full pitch set?
- What service access is required for tuning, hammer voicing, and damper
  regulation?

## Rejected From The Packet

- No dimensions.
- No tuning table.
- No bar lengths or resonator sizes.
- No hammer weights or action ratios.
- No CAD, DXF, G-code, or fabrication drawing.
- No claim that the concept is ready to build.

## Still Rejected For L2

- Full keyboard scale, pitch range, bar schedule, or tuning release.
- Bar geometry, support locations, hammer mass, or resonator dimensions.
- Action ratios, key spacing, damper lift values, or regulation settings.
- CAD, DXF, G-code, or fabrication drawing authority.
- Any L3/build-ready language.