Fix/from silence lego audio duration

[ChuxiJ]

This pull request refactors and clarifies how timing parameters are determined and sent for ACE-Step "lego" (stem) generation tasks, especially distinguishing between "from silence" and "context/cumulative" scenarios. The changes ensure the server receives accurate timing data, prevent regressions with mismatched durations, and improve code maintainability and test coverage.

Timing parameter computation and usage:

• Added a new module, legoApiTiming.ts, with the computeLegoTimingParams function to centralize the logic for calculating repainting_start, repainting_end, audio_duration, and chunk/full mode for lego tasks. This ensures correct values are sent based on whether generation is "from silence" or uses context.
• Updated generateClipInternal in generationPipeline.ts to use computeLegoTimingParams, ensuring all API calls use the correct timing fields and improving logging for debugging. [1] [2] [3]

Documentation and developer guidance:

• Added a detailed markdown document (release_task_lego_mapping.md) explaining the mapping between DAW state and ACE-Step API timing fields, chunk/full instruction logic, and the correct handling of placeholder silence WAVs. This helps prevent subtle bugs and clarifies expected behaviors.
• Improved inline documentation in silenceGenerator.ts to clarify the role of the placeholder silence WAV and direct developers to the new timing logic.

Testing and regression prevention:

• Added a comprehensive unit test suite (legoApiTiming.test.ts) to verify computeLegoTimingParams handles all expected scenarios and edge cases, protecting against regressions.

[Copilot]

Pull request overview

This PR centralizes and corrects how ACE-Step lego task timing fields are computed/sent, especially differentiating “from silence” vs “with context” generation to avoid duration mismatches when uploading a placeholder silence WAV.

Changes:

• Added computeLegoTimingParams to compute repainting_*, audio_duration, and chunk/full instruction mode consistently.
• Updated generateClipInternal to use the centralized timing computation and improved debug logging of timing values.
• Added unit tests and documentation describing the DAW → /release_task timing field mapping and placeholder silence behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/services/legoApiTiming.ts	New centralized timing computation for lego tasks (from-silence vs context).
src/services/generationPipeline.ts	Uses computeLegoTimingParams when building lego task params and instruction text; improves timing logging.
src/services/silenceGenerator.ts	Clarifies that silence WAV is a small placeholder and real duration comes from audio_duration.
tests/unit/legoApiTiming.test.ts	Unit coverage for the new timing computation behavior and overrides.
docs/release_task_lego_mapping.md	Developer-facing explanation of timing field mapping and regression to avoid.

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[Copilot]

generateSilenceWav intentionally uploads a fixed 0.1s placeholder and ignores its argument (see its _durationSeconds param). Passing timing.audio_duration here reads like it affects the generated blob length and can mislead future changes; consider either removing the parameter from generateSilenceWav (or renaming the function to indicate it's a placeholder), or pass a constant (e.g. 0) and rely exclusively on audio_duration in the task params.

Suggested change

	const srcAudioBlob = srcBlob ?? generateSilenceWav(timing.audio_duration);
	const srcAudioBlob = srcBlob ?? generateSilenceWav(0);

[Copilot]

generateSilenceWav takes a _durationSeconds argument but the implementation ignores it and always generates a fixed 0.1s placeholder WAV. To avoid confusion (especially now that call sites pass meaningful durations), consider removing this parameter from the public API or renaming it to make it explicit that it's unused/placeholder-only.

Suggested change

	* seconds). This file only uploads a tiny placeholder (0.1s at 16kHz mono ≈ 3.2KB).
	*/
	export function generateSilenceWav(_durationSeconds: number): Blob {
	* seconds). This file only uploads a tiny placeholder (0.1s at 16kHz mono ≈ 3.2KB),
	* regardless of the provided duration argument.
	*
	* NOTE: `_placeholderDurationSeconds` is accepted only for API symmetry with other
	* audio generators; it is intentionally ignored when constructing the WAV and should
	* not be relied upon to control the output duration.
	*/
	export function generateSilenceWav(_placeholderDurationSeconds: number): Blob {