fix: tempo-driven audio region resizing and playhead clamping

src/core/commands/global-region/GlobalTempoCommands.test.ts

@@ -2,7 +2,9 @@ import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { KGCore } from '../../KGCore';
 import { KGProject } from '../../KGProject';
 import { GlobalTrackType } from '../../global-track';
+import { KGAudioRegion } from '../../region/KGAudioRegion';
 import { KGTempoRegion } from '../../region/KGTempoRegion';
+import { KGAudioTrack } from '../../track/KGAudioTrack';
 import { CreateTempoRegionCommand } from './CreateTempoRegionCommand';
 import { DeleteTempoRegionCommand } from './DeleteTempoRegionCommand';
 import { ResizeTempoRegionCommand } from './ResizeTempoRegionCommand';
@@ -118,4 +120,26 @@ describe('global tempo region commands', () => {
     command.undo();
     expect((tempoTrack.getRegions()[0] as KGTempoRegion).getBpm()).toBe(120);
   });
+
+  it('expands max bars when a tempo edit makes audio require more space', () => {
+    const project = KGCore.instance().getCurrentProject();
+    const tempoTrack = getTempoTrack();
+    tempoTrack.setRegions([
+      new KGTempoRegion('region', tempoTrack.getId(), tempoTrack.getTrackIndex(), 120, 0, 8, 4),
+    ]);
+
+    const audioTrack = new KGAudioTrack('Audio', 1);
+    audioTrack.setRegions([
+      new KGAudioRegion('audio', '1', 0, 'Audio', 28, 4, 'file', 'file.wav', 8, 0),
+    ]);
+    project.setTracks([audioTrack]);
+
+    const command = new UpdateTempoRegionCommand('region', 60);
+    command.execute();
+    expect(project.getMaxBars()).toBe(9);
+    expect((audioTrack.getRegions()[0] as KGAudioRegion).getLength()).toBeCloseTo(8);
+    command.undo();
+    expect(project.getMaxBars()).toBe(8);
+    expect((audioTrack.getRegions()[0] as KGAudioRegion).getLength()).toBeCloseTo(4);
+  });
 });

src/core/commands/global-region/UpdateTempoRegionCommand.ts

@@ -2,13 +2,23 @@ import { KGCommand } from '../KGCommand';
 import { KGCore } from '../../KGCore';
 import { GlobalTrackType } from '../../global-track';
 import { KGTempoRegion } from '../../region/KGTempoRegion';
-import { findGlobalTrackByType } from '../../../util/globalTrackUtil';
+import {
+  findGlobalTrackByType,
+  getRequiredMaxBarsForAudioRegions,
+  normalizeTempoRegionsForProject,
+  restoreAudioRegionLengths,
+  syncAudioRegionLengthsToPlaybackDuration,
+  type AudioRegionLengthSnapshot,
+} from '../../../util/globalTrackUtil';
 
 export class UpdateTempoRegionCommand extends KGCommand {
   private readonly regionId: string;
   private readonly nextBpm: number;
   private previousBpm: number | null = null;
+  private previousMaxBars: number | null = null;
+  private nextMaxBars: number | null = null;
   private targetRegion: KGTempoRegion | null = null;
+  private audioRegionLengthSnapshots: AudioRegionLengthSnapshot[] = [];
 
   constructor(regionId: string, nextBpm: number) {
     super();
@@ -30,15 +40,32 @@ export class UpdateTempoRegionCommand extends KGCommand {
 
     this.targetRegion = region;
     this.previousBpm = region.getBpm();
+    this.previousMaxBars = project.getMaxBars();
     region.setBpm(this.nextBpm);
+    this.audioRegionLengthSnapshots = syncAudioRegionLengthsToPlaybackDuration(project);
+
+    const requiredMaxBars = getRequiredMaxBarsForAudioRegions(project);
+    this.nextMaxBars = Math.max(project.getMaxBars(), requiredMaxBars);
+    if (this.nextMaxBars > project.getMaxBars()) {
+      project.setMaxBars(this.nextMaxBars);
+      normalizeTempoRegionsForProject(project);
+    }
   }
 
   undo(): void {
-    if (!this.targetRegion || this.previousBpm === null) {
+    if (!this.targetRegion || this.previousBpm === null || this.previousMaxBars === null) {
       throw new Error('Cannot undo tempo update without previous state');
     }
 
+    const project = KGCore.instance().getCurrentProject();
     this.targetRegion.setBpm(this.previousBpm);
+    if (project.getMaxBars() !== this.previousMaxBars) {
+      project.setMaxBars(this.previousMaxBars);
+      normalizeTempoRegionsForProject(project);
+    }
+    if (this.audioRegionLengthSnapshots.length > 0) {
+      restoreAudioRegionLengths(this.audioRegionLengthSnapshots);
+    }
   }
 
   getDescription(): string {

src/core/commands/global-region/WriteTempoTrackCommand.test.ts

@@ -2,7 +2,9 @@ import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { KGCore } from '../../KGCore';
 import { KGProject } from '../../KGProject';
 import { GlobalTrackType } from '../../global-track';
+import { KGAudioRegion } from '../../region/KGAudioRegion';
 import { KGTempoRegion } from '../../region/KGTempoRegion';
+import { KGAudioTrack } from '../../track/KGAudioTrack';
 import { WriteTempoTrackCommand } from './WriteTempoTrackCommand';
 
 describe('WriteTempoTrackCommand', () => {
@@ -90,4 +92,26 @@ describe('WriteTempoTrackCommand', () => {
       { bpm: 128, startBar: 2, lengthBars: 6 },
     ]);
   });
+
+  it('expands max bars when the rebuilt tempo map makes audio overflow', () => {
+    const project = KGCore.instance().getCurrentProject();
+    const audioTrack = new KGAudioTrack('Audio', 1);
+    audioTrack.setRegions([
+      new KGAudioRegion('audio', '1', 0, 'Audio', 28, 4, 'file', 'file.wav', 8, 0),
+    ]);
+    project.setTracks([audioTrack]);
+
+    const command = new WriteTempoTrackCommand(60, []);
+    command.execute();
+
+    expect(project.getBpm()).toBe(60);
+    expect(project.getMaxBars()).toBe(9);
+    expect((audioTrack.getRegions()[0] as KGAudioRegion).getLength()).toBeCloseTo(8);
+
+    command.undo();
+
+    expect(project.getBpm()).toBe(120);
+    expect(project.getMaxBars()).toBe(8);
+    expect((audioTrack.getRegions()[0] as KGAudioRegion).getLength()).toBeCloseTo(4);
+  });
 });

src/core/commands/global-region/WriteTempoTrackCommand.ts

@@ -5,8 +5,13 @@ import { KGTempoRegion } from '../../region/KGTempoRegion';
 import {
   cloneTempoRegions,
   findGlobalTrackByType,
+  getRequiredMaxBarsForAudioRegions,
   getSongEndBar,
   getSortedTempoRegions,
+  normalizeTempoRegionsForProject,
+  restoreAudioRegionLengths,
+  syncAudioRegionLengthsToPlaybackDuration,
+  type AudioRegionLengthSnapshot,
 } from '../../../util/globalTrackUtil';
 import { generateUniqueId } from '../../../util/miscUtil';
 
@@ -24,7 +29,10 @@ export class WriteTempoTrackCommand extends KGCommand {
   private readonly replacements: WriteTempoEntry[];
   private previousRegions: KGTempoRegion[] | null = null;
   private previousProjectBpm: number | null = null;
+  private previousMaxBars: number | null = null;
   private nextRegions: KGTempoRegion[] | null = null;
+  private nextMaxBars: number | null = null;
+  private audioRegionLengthSnapshots: AudioRegionLengthSnapshot[] = [];
 
   constructor(baseBpm: number, replacements: WriteTempoEntry[]) {
     super();
@@ -46,17 +54,29 @@ export class WriteTempoTrackCommand extends KGCommand {
     if (this.nextRegions) {
       project.setBpm(this.baseBpm);
       track.setRegions(cloneRegions(this.nextRegions, beatsPerBar));
+      syncAudioRegionLengthsToPlaybackDuration(project);
+      if (this.nextMaxBars !== null) {
+        project.setMaxBars(this.nextMaxBars);
+        normalizeTempoRegionsForProject(project);
+      }
       return;
     }
 
     const currentRegions = getSortedTempoRegions(track, beatsPerBar);
     this.previousProjectBpm = project.getBpm();
+    this.previousMaxBars = project.getMaxBars();
     this.previousRegions = cloneRegions(currentRegions, beatsPerBar);
     project.setBpm(this.baseBpm);
 
     if (this.replacements.length === 0) {
       this.nextRegions = [];
       track.setRegions([]);
+      this.audioRegionLengthSnapshots = syncAudioRegionLengthsToPlaybackDuration(project);
+      this.nextMaxBars = getRequiredMaxBarsForAudioRegions(project);
+      if (this.nextMaxBars > project.getMaxBars()) {
+        project.setMaxBars(this.nextMaxBars);
+        normalizeTempoRegionsForProject(project);
+      }
       return;
     }
 
@@ -64,6 +84,7 @@ export class WriteTempoTrackCommand extends KGCommand {
     if (songEndBar <= 0) {
       this.nextRegions = [];
       track.setRegions([]);
+      this.nextMaxBars = getRequiredMaxBarsForAudioRegions(project);
       return;
     }
 
@@ -119,10 +140,16 @@ export class WriteTempoTrackCommand extends KGCommand {
 
     this.nextRegions = nextRegions;
     track.setRegions(cloneRegions(this.nextRegions, beatsPerBar));
+    this.audioRegionLengthSnapshots = syncAudioRegionLengthsToPlaybackDuration(project);
+    this.nextMaxBars = getRequiredMaxBarsForAudioRegions(project);
+    if (this.nextMaxBars > project.getMaxBars()) {
+      project.setMaxBars(this.nextMaxBars);
+      normalizeTempoRegionsForProject(project);
+    }
   }
 
   undo(): void {
-    if (!this.previousRegions || this.previousProjectBpm === null) {
+    if (!this.previousRegions || this.previousProjectBpm === null || this.previousMaxBars === null) {
       throw new Error('Cannot undo tempo write without original state');
     }
 
@@ -134,7 +161,12 @@ export class WriteTempoTrackCommand extends KGCommand {
     }
 
     project.setBpm(this.previousProjectBpm);
+    project.setMaxBars(this.previousMaxBars);
     track.setRegions(cloneRegions(this.previousRegions, beatsPerBar));
+    normalizeTempoRegionsForProject(project);
+    if (this.audioRegionLengthSnapshots.length > 0) {
+      restoreAudioRegionLengths(this.audioRegionLengthSnapshots);
+    }
   }
 
   getDescription(): string {

src/core/commands/project/ChangeProjectPropertyCommand.ts

@@ -2,7 +2,13 @@ import { KGCommand } from '../KGCommand';
 import { KGCore } from '../../KGCore';
 import { KGProject, type KeySignature } from '../../KGProject';
 import type { TimeSignature } from '../../../types/projectTypes';
-import { normalizeTempoRegionsForProject } from '../../../util/globalTrackUtil';
+import {
+  getRequiredMaxBarsForAudioRegions,
+  normalizeTempoRegionsForProject,
+  restoreAudioRegionLengths,
+  syncAudioRegionLengthsToPlaybackDuration,
+  type AudioRegionLengthSnapshot,
+} from '../../../util/globalTrackUtil';
 
 /**
  * Interface defining properties that can be updated on a project
@@ -26,12 +32,25 @@ export class ChangeProjectPropertyCommand extends KGCommand {
   private originalProperties: ProjectUpdateProperties = {};
   private targetProject: KGProject | null = null;
   private changedProperties: Set<keyof ProjectUpdateProperties> = new Set();
+  private audioRegionLengthSnapshots: AudioRegionLengthSnapshot[] = [];
 
   constructor(properties: ProjectUpdateProperties) {
     super();
     this.newProperties = properties;
   }
 
+  private clampPlayheadToSongEndIfNeeded(): void {
+    if (!this.targetProject) {
+      return;
+    }
+
+    const core = KGCore.instance();
+    const songEndBeat = this.targetProject.getMaxBars() * this.targetProject.getTimeSignature().numerator;
+    if (core.getPlayheadPosition() > songEndBeat) {
+      core.setPlayheadPosition(songEndBeat);
+    }
+  }
+
   execute(): void {
     const core = KGCore.instance();
     this.targetProject = core.getCurrentProject();
@@ -63,6 +82,7 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       normalizeTempoRegionsForProject(this.targetProject);
       this.changedProperties.add('maxBars');
       updatedProperties.push(`maxBars: ${this.originalProperties.maxBars} → ${this.newProperties.maxBars}`);
+      this.clampPlayheadToSongEndIfNeeded();
     }
 
     // Update currentBars
@@ -79,6 +99,19 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       updatedProperties.push(`bpm: ${this.originalProperties.bpm} → ${this.newProperties.bpm}`);
     }
 
+    if (this.changedProperties.has('bpm')) {
+      this.audioRegionLengthSnapshots = syncAudioRegionLengthsToPlaybackDuration(this.targetProject);
+      const requiredMaxBars = getRequiredMaxBarsForAudioRegions(this.targetProject);
+      if (requiredMaxBars > this.targetProject.getMaxBars()) {
+        this.targetProject.setMaxBars(requiredMaxBars);
+        normalizeTempoRegionsForProject(this.targetProject);
+        this.changedProperties.add('maxBars');
+        if (this.originalProperties.maxBars !== requiredMaxBars) {
+          updatedProperties.push(`maxBars: ${this.originalProperties.maxBars} → ${requiredMaxBars}`);
+        }
+      }
+    }
+
     // Update time signature
     if (this.newProperties.timeSignature !== undefined) {
       const originalTS = this.originalProperties.timeSignature!;
@@ -88,8 +121,10 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       if (originalTS.numerator !== newTS.numerator || originalTS.denominator !== newTS.denominator) {
         this.targetProject.setTimeSignature(newTS);
         normalizeTempoRegionsForProject(this.targetProject);
+        this.audioRegionLengthSnapshots = syncAudioRegionLengthsToPlaybackDuration(this.targetProject);
         this.changedProperties.add('timeSignature');
         updatedProperties.push(`timeSignature: ${originalTS.numerator}/${originalTS.denominator} → ${newTS.numerator}/${newTS.denominator}`);
+        this.clampPlayheadToSongEndIfNeeded();
       }
     }
 
@@ -133,6 +168,7 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       this.targetProject.setMaxBars(this.originalProperties.maxBars);
       normalizeTempoRegionsForProject(this.targetProject);
       restoredProperties.push(`maxBars: ${this.originalProperties.maxBars}`);
+      this.clampPlayheadToSongEndIfNeeded();
     }
 
     // Restore currentBars (only if it was changed)
@@ -153,6 +189,7 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       normalizeTempoRegionsForProject(this.targetProject);
       const ts = this.originalProperties.timeSignature;
       restoredProperties.push(`timeSignature: ${ts.numerator}/${ts.denominator}`);
+      this.clampPlayheadToSongEndIfNeeded();
     }
 
     // Restore key signature (only if it was changed)
@@ -167,6 +204,10 @@ export class ChangeProjectPropertyCommand extends KGCommand {
       restoredProperties.push(`selectedMode: "${this.originalProperties.selectedMode}"`);
     }
 
+    if (this.audioRegionLengthSnapshots.length > 0) {
+      restoreAudioRegionLengths(this.audioRegionLengthSnapshots);
+    }
+
     console.log(`Restored project: ${restoredProperties.join(', ')}`);
   }
 

src/stores/projectStore.test.ts

@@ -5,6 +5,7 @@ import { KGMidiTrack } from '../core/track/KGMidiTrack';
 import { KGAudioTrack } from '../core/track/KGAudioTrack';
 import { KGAudioRegion } from '../core/region/KGAudioRegion';
 import { createDefaultGlobalTracks } from '../core/global-track';
+import { getAudioRegionDisplayLengthBeats } from '../util/globalTrackUtil';
 
 const pianoRollStateMocks = vi.hoisted(() => ({
   setSheetMusicViewEnabled: vi.fn(),
@@ -33,6 +34,7 @@ const toneMocks = vi.hoisted(() => {
 let mockTracks: KGTrack[] = [new KGMidiTrack('Track 1', 0, 'acoustic_grand_piano')];
 let mockIsMetronomeEnabled = false;
 let mockShowGlobalTracks = false;
+let mockPlayheadPosition = 0;
 const mockProject = {
   getTimeSignature: () => ({ numerator: 4, denominator: 4 }),
   getMaxBars: () => 32,
@@ -101,8 +103,10 @@ const mockCore = {
   clearSelectedItems: vi.fn(),
   getStatus: () => 'Ready',
   setStatus: vi.fn(),
-  getPlayheadPosition: () => 0,
+  getPlayheadPosition: () => mockPlayheadPosition,
-  setPlayheadPosition: vi.fn(),
+  setPlayheadPosition: vi.fn((position: number) => {
+    mockPlayheadPosition = position;
+  }),
   getIsPlaying: () => false,
   startPlaying: vi.fn().mockResolvedValue(undefined),
   stopPlaying: vi.fn().mockResolvedValue(undefined),
@@ -161,10 +165,13 @@ describe('projectStore piano roll state', () => {
     pianoRollStateMocks.setPianoRollZoom.mockReset();
     mockTracks = [new KGMidiTrack('Track 1', 0, 'acoustic_grand_piano')];
     currentProject = mockProject;
+    mockPlayheadPosition = 0;
     mockCore.startPlaying.mockReset();
     mockCore.startPlaying.mockResolvedValue(undefined);
     mockCore.stopPlaying.mockReset();
     mockCore.stopPlaying.mockResolvedValue(undefined);
+    mockCore.executeCommand.mockReset();
+    mockCore.setPlayheadPosition.mockClear();
     mockCore.undo.mockReset();
     mockCore.undo.mockReturnValue(true);
     mockCore.redo.mockReset();
@@ -591,4 +598,143 @@ describe('projectStore piano roll state', () => {
     expect(state.settingsReturnSidePanel).toBeNull();
     expect(state.lastActiveSidePanel).toBe('eventList');
   });
+
+  it('refreshes expanded max bars after BPM reduction', async () => {
+    const { KGAudioTrack: TestAudioTrack } = await import('../core/track/KGAudioTrack');
+    const { KGAudioRegion: TestAudioRegion } = await import('../core/region/KGAudioRegion');
+
+    const audioTrack = new TestAudioTrack('Audio 1', 1);
+    audioTrack.setTrackIndex(0);
+    const audioRegion = new TestAudioRegion('audio-region-1', '1', 0, 'clip.wav', 124, 4, 'audio-file-1.wav', 'clip.wav', 8, 0);
+    audioTrack.setRegions([audioRegion]);
+
+    let projectName = 'Test Project';
+    let bpm = 120;
+    let maxBars = 32;
+    let currentBars = 0;
+    let timeSignature = { numerator: 4, denominator: 4 };
+    let keySignature = 'C major';
+    let selectedMode = 'major';
+    const project = {
+      getName: () => projectName,
+      setName: (value: string) => { projectName = value; },
+      getMaxBars: () => maxBars,
+      setMaxBars: (value: number) => { maxBars = value; },
+      getCurrentBars: () => currentBars,
+      setCurrentBars: (value: number) => { currentBars = value; },
+      getTimeSignature: () => timeSignature,
+      setTimeSignature: (value: { numerator: number; denominator: number }) => { timeSignature = value; },
+      getBarWidthMultiplier: () => 1,
+      getTracks: () => [audioTrack],
+      getGlobalTracks: () => createDefaultGlobalTracks(),
+      getBpm: () => bpm,
+      setBpm: (value: number) => { bpm = value; },
+      getKeySignature: () => keySignature,
+      setKeySignature: (value: string) => { keySignature = value; },
+      getSelectedMode: () => selectedMode,
+      setSelectedMode: (value: string) => { selectedMode = value; },
+      getIsLooping: () => false,
+      getIsMetronomeEnabled: () => false,
+      setIsMetronomeEnabled: vi.fn(),
+      getShowGlobalTracks: () => false,
+      setShowGlobalTracks: vi.fn(),
+      getLoopingRange: () => [0, 0] as [number, number],
+      getPianoRollZoom: () => 1,
+    };
+    currentProject = project as unknown as typeof mockProject;
+    mockCore.executeCommand.mockImplementation((command: { execute: () => void }) => command.execute());
+
+    const { useProjectStore } = await import('./projectStore');
+
+    act(() => {
+      useProjectStore.getState().setBpm(60);
+    });
+
+    const state = useProjectStore.getState();
+    expect(bpm).toBe(60);
+    expect(maxBars).toBe(33);
+    expect(state.maxBars).toBe(33);
+    expect(audioRegion.getLength()).toBeCloseTo(8);
+    expect(getAudioRegionDisplayLengthBeats(project as any, audioRegion)).toBeCloseTo(8);
+  });
+
+  it('does not auto-shrink max bars after BPM increase', async () => {
+    const { KGAudioTrack: TestAudioTrack } = await import('../core/track/KGAudioTrack');
+    const { KGAudioRegion: TestAudioRegion } = await import('../core/region/KGAudioRegion');
+
+    const audioTrack = new TestAudioTrack('Audio 1', 1);
+    audioTrack.setTrackIndex(0);
+    audioTrack.setRegions([
+      new TestAudioRegion('audio-region-1', '1', 0, 'clip.wav', 124, 8, 'audio-file-1.wav', 'clip.wav', 4, 0),
+    ]);
+
+    let projectName = 'Test Project';
+    let bpm = 120;
+    let maxBars = 40;
+    let currentBars = 0;
+    let timeSignature = { numerator: 4, denominator: 4 };
+    let keySignature = 'C major';
+    let selectedMode = 'major';
+    const project = {
+      getName: () => projectName,
+      setName: (value: string) => { projectName = value; },
+      getMaxBars: () => maxBars,
+      setMaxBars: (value: number) => { maxBars = value; },
+      getCurrentBars: () => currentBars,
+      setCurrentBars: (value: number) => { currentBars = value; },
+      getTimeSignature: () => timeSignature,
+      setTimeSignature: (value: { numerator: number; denominator: number }) => { timeSignature = value; },
+      getBarWidthMultiplier: () => 1,
+      getTracks: () => [audioTrack],
+      getGlobalTracks: () => createDefaultGlobalTracks(),
+      getBpm: () => bpm,
+      setBpm: (value: number) => { bpm = value; },
+      getKeySignature: () => keySignature,
+      setKeySignature: (value: string) => { keySignature = value; },
+      getSelectedMode: () => selectedMode,
+      setSelectedMode: (value: string) => { selectedMode = value; },
+      getIsLooping: () => false,
+      getIsMetronomeEnabled: () => false,
+      setIsMetronomeEnabled: vi.fn(),
+      getShowGlobalTracks: () => false,
+      setShowGlobalTracks: vi.fn(),
+      getLoopingRange: () => [0, 0] as [number, number],
+      getPianoRollZoom: () => 1,
+    };
+    currentProject = project as unknown as typeof mockProject;
+    mockCore.executeCommand.mockImplementation((command: { execute: () => void }) => command.execute());
+
+    const { useProjectStore } = await import('./projectStore');
+
+    act(() => {
+      useProjectStore.getState().setBpm(180);
+    });
+
+    const state = useProjectStore.getState();
+    expect(bpm).toBe(180);
+    expect(maxBars).toBe(40);
+    expect(state.maxBars).toBe(40);
+    expect((audioTrack.getRegions()[0] as KGAudioRegion).getLength()).toBeCloseTo(12);
+  });
+
+  it('moves the playhead to the song end when max bars shrink past it', async () => {
+    const { KGProject } = await import('../core/KGProject');
+    mockPlayheadPosition = 124;
+
+    currentProject = new KGProject('Test Project', 32, 0, 120) as unknown as typeof mockProject;
+    mockCore.executeCommand.mockImplementation((command: { execute: () => void }) => command.execute());
+
+    const { useProjectStore } = await import('./projectStore');
+
+    act(() => {
+      useProjectStore.getState().setMaxBars(16);
+    });
+
+    const state = useProjectStore.getState();
+    expect(currentProject.getMaxBars()).toBe(16);
+    expect(mockPlayheadPosition).toBe(64);
+    expect(mockCore.setPlayheadPosition).toHaveBeenCalledWith(64);
+    expect(state.maxBars).toBe(16);
+    expect(state.playheadPosition).toBe(64);
+  });
 });

src/stores/projectStore.ts

@@ -1553,8 +1553,7 @@ export const useProjectStore = create<ProjectState>((set, get) => {
         const command = new ChangeProjectPropertyCommand({ bpm });
         KGCore.instance().executeCommand(command);
 
-        // Update the store state
+        get().refreshProjectState();
-        set({ bpm });
         get().bumpAudioWaveformRedrawVersion();
 
         console.log(`Set BPM to ${bpm}`);
@@ -1570,10 +1569,7 @@ export const useProjectStore = create<ProjectState>((set, get) => {
         const command = new ChangeProjectPropertyCommand({ maxBars });
         KGCore.instance().executeCommand(command);
 
-        // Update the store state
+        get().refreshProjectState();
-        set({ maxBars });
-        // Sync CSS var so layout adjusts immediately
-        updateMaxBarsCSS(maxBars);
 
         console.log(`Set max bars to ${maxBars}`);
       } catch (error) {
@@ -1973,6 +1969,7 @@ export const useProjectStore = create<ProjectState>((set, get) => {
         selectedMode: project.getSelectedMode(),
         isMetronomeEnabled: project.getIsMetronomeEnabled(),
         showGlobalTracks: project.getShowGlobalTracks(),
+        playheadPosition: core.getPlayheadPosition(),
         currentTime: formatCurrentTime(project, core.getPlayheadPosition()),
       });
 

src/util/globalTrackUtil.test.ts

@@ -3,7 +3,8 @@ import { KGProject } from '../core/KGProject';
 import { GlobalTrackType } from '../core/global-track';
 import { KGAudioRegion } from '../core/region/KGAudioRegion';
 import { KGTempoRegion } from '../core/region/KGTempoRegion';
-import { beatRangeToSeconds, beatToSeconds, getAudioRegionDisplayLengthBeats, getEffectiveBpmAtBeat, normalizeTempoRegionsForProject, secondsToBeat } from './globalTrackUtil';
+import { KGAudioTrack } from '../core/track/KGAudioTrack';
+import { beatRangeToSeconds, beatToSeconds, getAudioRegionDisplayLengthBeats, getEffectiveBpmAtBeat, getRequiredMaxBarsForAudioRegions, normalizeTempoRegionsForProject, secondsToBeat, syncAudioRegionLengthsToPlaybackDuration } from './globalTrackUtil';
 
 describe('globalTrackUtil tempo helpers', () => {
   it('falls back to project bpm when no tempo regions exist', () => {
@@ -72,4 +73,73 @@ describe('globalTrackUtil tempo helpers', () => {
     const region = new KGAudioRegion('audio', 'track-1', 0, 'Audio', 0, 48, 'file', 'file.wav', 24, 0);
     expect(getAudioRegionDisplayLengthBeats(project, region)).toBeCloseTo(32);
   });
+
+  it('computes required bars for a slower project BPM change', () => {
+    const project = new KGProject('Tempo', 8, 0, 60);
+    const track = new KGAudioTrack('Audio', 1);
+    track.setRegions([
+      new KGAudioRegion('audio', '1', 0, 'Audio', 28, 4, 'file', 'file.wav', 8, 0),
+    ]);
+    project.setTracks([track]);
+
+    expect(getRequiredMaxBarsForAudioRegions(project)).toBe(9);
+  });
+
+  it('computes required bars from playable audio after clip offset', () => {
+    const project = new KGProject('Tempo', 8, 0, 60);
+    const track = new KGAudioTrack('Audio', 1);
+    track.setRegions([
+      new KGAudioRegion('audio', '1', 0, 'Audio', 28, 4, 'file', 'file.wav', 10, 6),
+    ]);
+    project.setTracks([track]);
+
+    expect(getRequiredMaxBarsForAudioRegions(project)).toBe(8);
+  });
+
+  it('uses the farthest audio region end when multiple regions are present', () => {
+    const project = new KGProject('Tempo', 8, 0, 60);
+    const track = new KGAudioTrack('Audio', 1);
+    track.setRegions([
+      new KGAudioRegion('audio-a', '1', 0, 'Audio A', 24, 4, 'file-a', 'a.wav', 4, 0),
+      new KGAudioRegion('audio-b', '1', 0, 'Audio B', 28, 4, 'file-b', 'b.wav', 12, 0),
+    ]);
+    project.setTracks([track]);
+
+    expect(getRequiredMaxBarsForAudioRegions(project)).toBe(10);
+  });
+
+  it('extends beyond the current song end using the trailing tempo region BPM', () => {
+    const project = new KGProject('Tempo', 8, 0, 120);
+    const tempoTrack = project.getGlobalTracks().find(track => track.getType() === GlobalTrackType.Tempo);
+    if (!tempoTrack) {
+      throw new Error('Tempo track missing');
+    }
+
+    tempoTrack.setRegions([
+      new KGTempoRegion('a', tempoTrack.getId(), tempoTrack.getTrackIndex(), 120, 0, 4, 4),
+      new KGTempoRegion('b', tempoTrack.getId(), tempoTrack.getTrackIndex(), 60, 4, 4, 4),
+    ]);
+
+    const track = new KGAudioTrack('Audio', 1);
+    track.setRegions([
+      new KGAudioRegion('audio', '1', 0, 'Audio', 28, 4, 'file', 'file.wav', 8, 0),
+    ]);
+    project.setTracks([track]);
+
+    expect(getRequiredMaxBarsForAudioRegions(project)).toBe(9);
+  });
+
+  it('syncs stored audio region length to the tempo-aware playback duration', () => {
+    const project = new KGProject('Tempo', 16, 0, 120);
+    const track = new KGAudioTrack('Audio', 1);
+    const region = new KGAudioRegion('audio', '1', 0, 'Audio', 0, 24, 'file', 'file.wav', 12, 0);
+    track.setRegions([region]);
+    project.setTracks([track]);
+
+    project.setBpm(240);
+    syncAudioRegionLengthsToPlaybackDuration(project);
+
+    expect(region.getLength()).toBeCloseTo(48);
+    expect(getAudioRegionDisplayLengthBeats(project, region)).toBeCloseTo(48);
+  });
 });

src/util/globalTrackUtil.ts

@@ -13,6 +13,11 @@ import { KGTempoRegion } from '../core/region/KGTempoRegion';
 
 export const DEFAULT_MARKER_REGION_NAME = 'Marker';
 
+export interface AudioRegionLengthSnapshot {
+  region: KGAudioRegion;
+  length: number;
+}
+
 export function ensureDefaultGlobalTracks(project: KGProject): KGGlobalTrack[] {
   const existingTracks = project.getGlobalTracks?.() ?? [];
   const nextTracks = createDefaultGlobalTracks();
@@ -360,8 +365,76 @@ export function getAudioRegionDisplayLengthBeats(project: KGProject, region: KGA
   }
 
   const startBeat = region.getStartFromBeat();
-  const beatBoundSeconds = beatRangeToSeconds(project, startBeat, startBeat + region.getLength());
   const availableAudioSeconds = Math.max(0, region.getAudioDurationSeconds() - region.getClipStartOffsetSeconds());
-  const visibleSeconds = Math.min(beatBoundSeconds, availableAudioSeconds);
+  const endBeat = getAudioRegionPlaybackEndBeat(project, region);
-  return Math.max(0, secondsToBeat(project, beatToSeconds(project, startBeat) + visibleSeconds) - startBeat);
+  return Math.max(0, endBeat - startBeat);
+}
+
+export function getAudioRegionPlaybackEndBeat(project: KGProject, region: KGAudioRegion): number {
+  const startBeat = region.getStartFromBeat();
+  const availableAudioSeconds = Math.max(0, region.getAudioDurationSeconds() - region.getClipStartOffsetSeconds());
+  if (availableAudioSeconds <= 0) {
+    return startBeat;
+  }
+
+  const targetSeconds = beatToSeconds(project, startBeat) + availableAudioSeconds;
+  const songEndBeat = getSongEndBeat(project);
+  const songEndSeconds = beatToSeconds(project, songEndBeat);
+
+  if (targetSeconds <= songEndSeconds) {
+    return secondsToBeat(project, targetSeconds);
+  }
+
+  const tailBpm = getEffectiveBpmAtBeat(project, Math.max(0, songEndBeat - 1e-6));
+  return songEndBeat + ((targetSeconds - songEndSeconds) / (60 / tailBpm));
+}
+
+export function getRequiredMaxBarsForAudioRegions(project: KGProject): number {
+  const beatsPerBar = project.getTimeSignature().numerator;
+  let requiredBars = project.getMaxBars();
+
+  for (const track of project.getTracks()) {
+    for (const region of track.getRegions()) {
+      if (!(region instanceof KGAudioRegion)) {
+        continue;
+      }
+
+      const regionEndBeat = getAudioRegionPlaybackEndBeat(project, region);
+      const regionRequiredBars = Math.ceil(regionEndBeat / beatsPerBar);
+      requiredBars = Math.max(requiredBars, regionRequiredBars);
+    }
+  }
+
+  return requiredBars;
+}
+
+export function syncAudioRegionLengthsToPlaybackDuration(project: KGProject): AudioRegionLengthSnapshot[] {
+  const changedRegions: AudioRegionLengthSnapshot[] = [];
+
+  for (const track of project.getTracks()) {
+    for (const region of track.getRegions()) {
+      if (!(region instanceof KGAudioRegion)) {
+        continue;
+      }
+
+      const nextLength = Math.max(0, getAudioRegionPlaybackEndBeat(project, region) - region.getStartFromBeat());
+      if (region.getLength() === nextLength) {
+        continue;
+      }
+
+      changedRegions.push({
+        region,
+        length: region.getLength(),
+      });
+      region.setLength(nextLength);
+    }
+  }
+
+  return changedRegions;
+}
+
+export function restoreAudioRegionLengths(snapshots: AudioRegionLengthSnapshot[]): void {
+  snapshots.forEach(({ region, length }) => {
+    region.setLength(length);
+  });
 }