Audio mixer loop cursor reset misses bounds re-check

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Issue #718 filed: "[Audit][High] Mixer loop cursor reset skips bounds re-check, risking OOB read and audio artifacts"

Key finding in modules/engine-audio/src/backends/sdl_audio.zig:265:

In Mixer.mix(), when a looping voice reaches end-of-buffer and voice.cursor = 0.0 is set at line 267, the loop continues without a continue statement. This means execution falls through to pos_idx * 2 + 2 > u8_buf.len check using a stale pos_idx (calculated before cursor reset). After looping, the bounds check at line 276 recalculates valid_pos_idx from the reset cursor, but the flow between lines 267-275 is problematic — if pos_idx was near the end of buffer and voice.cursor reset to 0, the check could pass when it shouldn't, leading to an incorrect sample read before proper recalculation.

The fix: add continue after voice.cursor = 0.0 to skip the rest of the iteration and let the next loop properly recalculate pos_idx from the reset cursor.

Triggered by scheduled workflow

opencode session  |  github run

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