122b fast2 4/7 — headless-terminal ERR: fast-fail cap == declared×mult collision (cap-design lesson)

Fourth job of the 122b fast2 one-task-per-job sequence, and a harness lesson: a fast-fail cap must sit STRICTLY BELOW the task's declared timeout × AGENT_TIMEOUT_MULT. headless-terminal declares 900s; ×2.0 = 1800s = exactly the cap this run used. Both timers fired at 30m00s and Harbor's own AgentTimeoutError won the race, so the trial ERRORED (exception recorded, NEVER VERIFIED) instead of taking the fast-timeout path (exit 0 → verifier scores the on-disk state). The agent/fast-timeout.json marker (exit_code 124) landed anyway — both mechanisms triggered, Harbor's classification took precedence.

The agent worked the full 30 min (1.72M in / 28.7k out) without declaring done. Rerun with cap 1700 (100s under the ceiling) as sequence job 7 → fast2__qwen3.5-122b-a10b__20260712-180346, which got a scored verdict. Ledger item added: validate cap maps against declared×mult at run start.