fix(playback): throttle legacy bridge-hit recording; emit loop-set for manual A/B

[OmikronApex]

Problem

The capability inspector showed playback.loop-api firing dozens of times per second — even with no song playing.

Root cause chain:

• note_detect's HUD ticks every 33 ms and called window.slopsmith.getLoop() per tick (a legitimately cheap read when it was written).
• Core instruments every window.feedBack.getLoop() call as a legacy bridge hit: compat-shim bookkeeping, a playback:bridge-hit event, and a diagnostics snapshot rebuild + JSON.stringify per call.
• Result: ~30 snapshot serializations/sec on the main thread while idle, and a saturated hitCount drowning genuine legacy-surface signal.

Fix

• _recordPlaybackBridge now throttles per bridgeId|surface (5 s window). First call records immediately; repeats inside the window are dropped. Bridge hits are a "this surface is still in use" signal, not a call counter.
• setLoopEnd() (manual A/B buttons) now emits the same loop-set transport event as setLoop(), so plugins can go event-driven via playback:loop-set / playback:loop-cleared instead of polling getLoop() — polling was the only way to see button-armed loops before.

Companion PR in note_detect makes its drill sync event-driven with a 1 Hz fallback poll.

Testing

• node --check static/app.js
• All 924 JS tests pass (node --test tests/js/*.test.js)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Throttled repeated legacy playback bridge hits to reduce overhead by limiting repeat bridge polling per bridge/surface within a 5-second window.
  • Updated manual A/B loop end control so it emits the same transport loop-set event as other loop actions (including the active loop payload), enabling plugins to react without polling.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between 37eeb9c and 8c23270.

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• CHANGELOG.md
• static/app.js

🚧 Files skipped from review as they are similar to previous changes (1)

• static/app.js

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📝 Walkthrough

Walkthrough

The playback bridge recording function now throttles repeated hits per bridge/surface pair. The manual A/B loop control setLoopEnd() now emits a loop-set transport event, and the changelog records both changes.

Changes

Playback bridge and loop event fixes

Layer / File(s)	Summary
Bridge hit throttling static/app.js	_recordPlaybackBridge() now uses a Map to throttle recordBridgeHit calls per (bridgeId, legacySurface) pair to a 5s minimum interval.
Loop-set transport event emission static/app.js, CHANGELOG.md	setLoopEnd() now dispatches playback.transportEvent('loop-set', ...) with active loopA/loopB state, and the changelog documents both changes.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant AppJS as static/app.js
    participant Plugin

    User->>AppJS: setLoopEnd()
    AppJS->>AppJS: arm loopA/loopB
    AppJS->>Plugin: transportEvent('loop-set', loopA, loopB, loop payload)
    Plugin->>Plugin: react to playback:loop-set

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main changes: throttling legacy bridge-hit recording and emitting loop-set for manual A/B loops.
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.

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[coderabbitai]

🧹 Nitpick comments (1)

static/app.js (1)

5539-5563: 🚀 Performance & Scalability | 🔵 Trivial | 💤 Low value

Throttle logic looks correct.

Per-key throttling with a 5s window is implemented correctly (check-then-set ordering avoids allowing bursts). One minor note: _bridgeRecordLast is a module-level Map with no eviction, unlike playback.js's own bridges map which caps size via MAX_BRIDGES. In practice the key space (bridgeId/legacySurface pairs) is likely small and bounded, so this is unlikely to be a real problem, but consider capping it defensively if bridge identifiers can ever be dynamic/unbounded.

🤖 Prompt for 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.

In `@static/app.js` around lines 5539 - 5563, The per-surface throttling in
_recordPlaybackBridge uses a module-level _bridgeRecordLast Map that never
evicts entries, so add a bounded cleanup strategy or size cap similar to
playback.js’s bridged state handling. Update _recordPlaybackBridge and
_bridgeRecordLast so old bridgeId|legacySurface keys are removed or the map is
capped when identifiers can grow unbounded, keeping the 5s throttle behavior
intact.

🤖 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.

Nitpick comments:
In `@static/app.js`:
- Around line 5539-5563: The per-surface throttling in _recordPlaybackBridge
uses a module-level _bridgeRecordLast Map that never evicts entries, so add a
bounded cleanup strategy or size cap similar to playback.js’s bridged state
handling. Update _recordPlaybackBridge and _bridgeRecordLast so old
bridgeId|legacySurface keys are removed or the map is capped when identifiers
can grow unbounded, keeping the 5s throttle behavior intact.

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ℹ️ Review info

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Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e3ee0ae2-7f15-41dd-968f-78b0e7b1d0d2

📥 Commits

Reviewing files that changed from the base of the PR and between 115c352 and 37eeb9c.

📒 Files selected for processing (2)

• CHANGELOG.md
• static/app.js