fix: preserve audio beds in head slices

[Brad-Edwards]

Summary

Preserves composition audio-bed metadata when composition slices are truncated to their addressed head scene, so loop and scrub modes keep the declared bed while standalone remains explicitly suppressed.

Requirement UIDs

• (none — bug/refactor/maintenance run; see Traceability section below)

Related Issues

Closes #147

ADR Impact

• ADR-004
• ADR-017
• ADR-018
• ADR-020
• ADR-021

Changes

• Carry audioBed through the loader's head-only composition slice rebuild.
• Carry audioBed through the direct scene-navigation bridge head truncation path.
• Add loader regression coverage proving loop and scrub head slices construct and start the composition bed, while existing standalone suppression remains intact.
• Tighten the prompter audio bypass test so a lifecycle regression cannot be masked by an empty audio allowlist.

Test Plan

• Unit tests pass (make test)

• Integration tests pass if applicable (make integration)

• make check passes (Spotless, SpotBugs, Error Prone, Checkstyle, JaCoCo)

• No coverage regression

• pnpm test -- tests/runtime/scene-loader-audio.test.ts

• pnpm test -- tests/runtime/scene-loader-audio.test.ts tests/runtime/scene-navigation.test.ts

• pnpm lint && pnpm typecheck && pnpm test

• pre-commit run --all-files

Ground Control Checks

• make policy passes
• gc_evaluate_quality_gates passes or is unchanged by this repo-only change
• gc_run_sweep reviewed; findings fixed or recorded with rationale

Traceability

• IMPLEMENTS: Issue Composition audio beds are dropped in head-only composition modes #147 <- src/runtime/scene-loader.ts, Issue Composition audio beds are dropped in head-only composition modes #147 <- src/runtime/scene-navigation.ts
• TESTS: Issue Composition audio beds are dropped in head-only composition modes #147 <- tests/runtime/scene-loader-audio.test.ts

Checklist

• Code follows project coding standards (docs/CODING_STANDARDS.md)
• No business logic in API layer
• Domain layer has no framework imports
• Envers @Audited on new entities if applicable
• Changelog fragment added at changelog.d/147.fixed.md
• Architectural docs updated if stack, package structure, or key behaviors changed

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud