Fix auto duration mode incorrectly clamping to 15 seconds

[Copilot]

Auto duration mode (duration=-1) was being clamped to 15 seconds instead of allowing pipeline auto-detection (30-240s range). Root cause: max(15, min(240, -1)) evaluates to 15.

Changes

api/generate.py

• Conditional clamping: only apply 15-240s range to positive values
• Preserve -1/0 for auto-detection, normalize invalid negatives to -1

generate_ace.py

• generate_track_ace: Allow -1/0 values for auto-detection
• _run_ace_text2music: Preserve -1/0 for pipeline, validate negative inputs

docs/ACEFORGE_API.md

• Document auto-detection behavior for duration parameter

Technical Detail

Before:

duration = max(15, min(240, duration))  # -1 → 15

After:

if duration > 0:
    duration = max(15, min(240, duration))  # Clamp positive values only
elif duration < 0 and duration != -1:
    duration = -1  # Normalize invalid negatives
# -1 and 0 pass through to pipeline auto-detection (30-240s)

The pipeline's existing auto-detection logic (cdmf_pipeline_ace_step.py:2047-2049) now receives -1 as intended and randomly selects duration in 30-240s range.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Only generating 14s audio</issue_title>
<issue_description>v1.0.8 is only generating 14s audio when auto is selected. I think there's an issue with clamping:
Note the "UI may send duration=-1 or 0; clamp to valid range (15–240s)"</issue_description>

<agent_instructions>verify the user claim about "auto" setting cropping the generation length/duration </agent_instructions>

Comments on the Issue (you are @copilot in this section)

@lmangani Hello @riversedge thanks for the report! I seem to be able to generate any lenght audio by using the time selector - could you confirm what other generation settings you used for this test?

• Fixes Only generating 14s audio #48

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