Stop preset tests from waiting on the tail poll - #4089
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The agent's output goes to files rather than pipes, so reading it polls every 200ms, and every `run_preset_agent` call waited once after the agent had already exited. Tests write the whole output up front, so `test_agent.py` spent 2.5s of its 4.3s sleeping.
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What
The preset agent writes its output to files rather than pipes, so reading it means polling:
_FileLineReader._POLL_SECONDS = 0.2. When there is no new data and the agent process is still alive, the reader sleeps 200ms. Tests write the whole fake-agent output up front and the process exits in ~20ms, so everyrun_preset_agentcall waited out a full poll it had nothing to wait for.Tests that trigger a resume pay it 2-3 times, which matched the timings exactly:
An autouse fixture in the presets test package sets the interval to 0.
Effect
test_agent.pygoes from 4.18s to 1.65s, 41 passed. It was the most expensive test file in the suite.What remains is genuine:
test_creates_private_cli_home_and_dstack_wrapperspawns the realdstackCLI to prove the generated workspace wrapper executes, which cannot be shown without executing it.No production code changed.
Also
Two notes in AGENTS.md on keeping the suite fast, since this was the same class of issue as the lock-retry sleeps fixed in #4088.
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