feat(editor): DAW mixer console — vertical channel strips, live meters, +10 dB

[ChrisBeWithYou]

Correction PR (parity item) — the mixer/meters #285 features I'd deferred, ported faithfully to #285's design at Christian's direction (vertical channel strips in a bottom drawer, not my earlier docked-panel adaptation).

What changed

The docked mixer side-panel becomes #285's bottom mixer drawer: a horizontal row of vertical channel strips (one per stem + transcription part), each a live level meter beside a rotated fader, then the SOURCE / GUIDE / CLICK utility buses and a dedicated MASTER output strip. It rises on open, falls on close (reduced-motion aware), and opens closed each session (a per-screen view toggle, not a persisted pref).

• Live meters — an AnalyserNode taps each bus and per-stem gain (a zero-gain sink keeps the browser processing them silently). audioMixerMeterLevels reads RMS→(−60..0 dBFS) levels + peak dB each frame; the panel's rAF tick fills the bars with instant-attack/gravity-decay ballistics and a peak-hold clip readout.
• Master bus — a master gain sits post-limiter (limiter → masterGain → destination). The reference recording joins there too, so it's metered and master-trimmed but still never through the limiter — a hot recording is never colored.
• +6 dB headroom — the fader range is 0–106 (0–100 linear to unity, 100–106 a log map to +6 dB). partStripState/clapState resolve volume through _mixerGainForFaderPure, so stems and synth parts alike can be pushed to +6 dB; every fader reads its level in dB.
• Selection sync — the strip matching the selected Tracks-column row lights up.
• Removed the vestigial edit-blip toggle (functionally useless; feat(editor): add source-aware DAW track session #285 dropped it too).

Tests

• tests/mixer_meters.test.mjs (new, 4): the sample→level/peak math, the meter ballistics, and the dB readout label.
• tests/mixer_panel.test.mjs: reconciled to the +6 dB clamp, dB fader labels, the master bus, the animated close (instant in the unit env), and the always-closed init; a new fader-gain pure case.
• tests/audio_mixer.test.js + tests/loop_ab.test.js: the sliced-source envs inject the meter-tap stub, and the ref-routing assertion now expects refGain → masterGain → destination (still bypassing the limiter).

Gates: 184 JS suites, pytest 291 / 2 skipped, lint 0 errors / 3 baseline warnings.

⚠️ Interactive desktop verification pending — a build is being produced to eyeball the console + live meters.

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https://claude.ai/code/session_01EBQCHCNA81E9tHmSDHSe2Q

Summary by CodeRabbit

• New Features

  • Replaced the docked mixer with a bottom drawer featuring channel strips for tracks, SOURCE, GUIDE, CLICK, and MASTER.
  • Added live level and peak meters, track highlighting, and an “All tracks” playback control.
  • Faders now display dB values and provide up to +10 dB of headroom.
  • Recording is now metered and master-trimmed without being affected by limiter coloration.

• Bug Fixes

  • Improved meter cleanup when tracks or stems are reset.
  • Removed the obsolete edit-blip control.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: f82adce7-cca0-44d7-a4ba-e2249a044181

📥 Commits

Reviewing files that changed from the base of the PR and between c16b625 and e199123.

📒 Files selected for processing (12)

• CHANGELOG.md
• assets/v3-theme.css
• screen.html
• src/audio.js
• src/host.js
• src/main.js
• src/mixer-panel.js
• tests/audio_mixer.test.js
• tests/loop_ab.test.js
• tests/mixer_meter_teardown.test.js
• tests/mixer_meters.test.mjs
• tests/mixer_panel.test.mjs

---

📝 Walkthrough

Walkthrough

The mixer is replaced with a bottom-drawer channel-strip interface. Audio routing adds a post-limiter master bus, 0..110 dB fader headroom, analyser-based live metering, dB labels, host meter hooks, and updated lifecycle and regression tests.

Changes

Mixer audio and metering

Layer / File(s)	Summary
Audio metering and master routing src/audio.js, src/main.js, src/host.js, tests/audio_mixer.test.js, tests/loop_ab.test.js, tests/mixer_meter_teardown.test.js	Master routing, analyser taps, per-track meters, dB gain mapping, host callbacks, and related routing and teardown tests are added.
Fader model and drawer lifecycle src/mixer-panel.js, tests/mixer_panel.test.mjs, tests/mixer_meters.test.mjs	Faders use 0..110 positions with dB labels, live meter updates, master initialization, accessibility text, and animated or immediate drawer closing.
Bottom-drawer mixer interface screen.html, assets/v3-theme.css, CHANGELOG.md	The docked mixer is replaced by styled bottom-drawer track strips, utility buses, a master strip, meter readouts, and updated release notes.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Editor
  participant MixerPanel
  participant AudioMixer
  participant Host
  Editor->>MixerPanel: open bottom-drawer mixer
  MixerPanel->>AudioMixer: update fader level
  AudioMixer->>AudioMixer: route audio through masterGain
  MixerPanel->>Host: request mixerMeterLevels()
  Host->>AudioMixer: read analyser levels and peaks
  AudioMixer-->>Host: return bus and track meters
  Host-->>MixerPanel: provide live meter data

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Possibly related PRs

• got-feedBack/feedBack-plugin-editor#109: Shares mixer gain routing and reference-gain wiring changes.
• got-feedBack/feedBack-plugin-editor#213: Shares mixer-panel, host, and audio mixer integration.
• got-feedBack/feedBack-plugin-editor#280: Shares track-strip gain and all-tracks playback integration.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main mixer overhaul with vertical strips and live meters.

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• Commit unit tests in branch feat/editor-mixer-meters

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Actionable comments posted: 6

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@assets/v3-theme.css`:
- Around line 602-613: Update the opening animation behavior for `#plugin-editor`
.editor-mixer-drawer so reduced-motion users do not run editor-mixer-rise when
the drawer opens. Add an appropriate prefers-reduced-motion override while
preserving the existing closing-animation behavior and normal-motion
transitions.

In `@screen.html`:
- Around line 389-390: Update screen.html lines 389-390 so the
`#editor-mixer-play-all` button uses a dedicated full-text class instead of
.editor-mix-ms. In assets/v3-theme.css lines 619-633, scope the 18px titlebar
font-size rule to the close button and style the All tracks class with automatic
width and appropriate padding.

In `@src/mixer-panel.js`:
- Around line 200-202: Expose the formatted dB value through aria-valuetext for
every fader. In src/mixer-panel.js at lines 200-202, initialize generated track
sliders from _mixerFaderLabelPure(st.vol); at lines 292-296, set it when bus
sliders are seeded; and at lines 356-363, update it whenever the visible track
label changes. In screen.html at lines 397-424, add initial dB aria-valuetext
values for SOURCE, GUIDE, CLICK, and MASTER and keep them synchronized in the
bus input handler.
- Around line 215-228: Update _meterPeakForKey to mirror _mixerMeterInputPure:
return levels.ref for the active audio key and levels.guide for the active
transcription key, using the relevant active identifiers in its arguments or
call sites. Preserve existing bus and track peak handling, and apply the same
fallback behavior to the additional peak-readout path noted in the comment.

In `@tests/mixer_meter_teardown.test.js`:
- Line 24: Update the `_stemGainsReset` extraction in the test to capture the
complete function body, including the `stemGainNodes.clear()` call after the
loop. Replace the current brace-limited regex approach with parsing or matching
that accounts for nested braces, while preserving the existing function-size
assertion.

In `@tests/mixer_panel.test.mjs`:
- Around line 189-198: Update the test “bus faders seed from host.mixUiState on
open” to wrap the stub assignment and assertions in a try/finally block. In the
finally block, always restore the saved host.mixUiState value and close the
mixer panel with editorToggleMixerPanel(false, true), preserving the existing
assertions and setup.

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---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 07540a8c-0f33-4d86-bf5d-805fc202ef26

📥 Commits

Reviewing files that changed from the base of the PR and between dc58021 and c16b625.

📒 Files selected for processing (12)

• CHANGELOG.md
• assets/v3-theme.css
• screen.html
• src/audio.js
• src/host.js
• src/main.js
• src/mixer-panel.js
• tests/audio_mixer.test.js
• tests/loop_ab.test.js
• tests/mixer_meter_teardown.test.js
• tests/mixer_meters.test.mjs
• tests/mixer_panel.test.mjs

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[ChrisBeWithYou]

Product ruling applied (decision item 3 from the review): +10 dB of headroom on EVERY fader — the SOURCE/GUIDE/CLICK buses and MASTER now ride the same 0–110 scale as the channel strips (one pct→gain curve everywhere, no inert fader zones). 5c48b4d. Decision item 2 (#296 master = output bus, immune to track solo/mute) was already implemented in d15def8 — confirmed as the intended behavior. Item 1 (#297 Alt-click overlap): accepted as-is, no code change.

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