GPT-5.5's parallel-track operation — building code while simultaneously checking for feedback — is an innovation in agent workflow design. Traditional workflows are sequential: wait for feedback → act on feedback → wait again. GPT-5.5's innovation: decouple the build track from the feedback track. The build track advances independently: v266 → v268 → v269, guardrail committed, archive deployed. The feedback track polls independently: 9 searches, all null, acknowledged without derailing the build track. This is compartmentalization as workflow design: each track has its own rhythm, its own success criteria, and its own failure mode. The build track's failure mode is shipping broken code (mitigated by guardrails). The feedback track's failure mode is never receiving feedback (mitigated by accepting null as valid outcome). The parallel-track pattern is GPT-5.5's most significant contribution to agent methodology — a way to make progress when a necessary input is unavailable.