Make CLI error output concise and consistent

[anmarchenko]

What

Print CLI failures once on stderr without automatically dumping usage. For example, ddtest plan --unknown now prints the error and a ddtest plan --help hint instead of 27 lines ending with a duplicate FAILURE log.

Planner and runner handlers return errors through Cobra, preserving error codes and telemetry flushing. Exit status remains 1 on failure; explicit help and version output are unchanged.

Why

Repeated errors and unrelated flag listings obscure the action users need to take, particularly in CI logs. This follows the CLI guidelines for useful, low-noise errors.

E2E testing

• Passed GOTOOLCHAIN=go1.26.5 make test and GOTOOLCHAIN=go1.26.5 make lint.
• Built the CLI and verified plan --unknown, run --min-parallelism=nope, and an unknown subcommand print one error plus a help hint, write nothing to stdout, and exit 1. Running plan with Git absent from PATH prints one prerequisite error without usage or a duplicate log.
• Verified plan --help and --version still succeed. Regression tests cover these process-level behaviors, missing flag values, planner/runner errors, and telemetry flushing.

[datadog-datadog-prod-us1]

 

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 86.59% (+0.03%)

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