fix(server): cancel pending OpenCode prompts safely

Cancel pending SDK requests before aborting the native session. Preserve per-admission cancellation state and treat stopped initial prompts as interruption instead of provider failure.

Finding: R14 prompt cancellation

Model: GPT-5.6 Sol via Codex
1106aea50cJulius Marminge committed on 9/5/2026, 4:54:28 AMparentd4c2e78
2 files changedLine totals unavailable