HeadlessConsoleOptions.Resolve tested the environment variable against
the literal "1", so ACDREAM_HEADLESS_CONSOLE=0 silently fell through to
the terminal-shaped default (on when stdin is a real console) instead of
acting as an A/B off-switch. Now: once the variable is SET AT ALL, any
value other than "0" enables and "0" disables -- the same idiom
ACDREAM_RETAIL_CLOSE_DEGRADES / ACDREAM_RETAIL_UI already use. An unset
variable still falls through to the terminal default.
Registered the flag as the sixth entry in
LaunchOptionsDocumentationTests.DefaultOnBehaviorFlags and updated the
Conventions section of docs/launch-options.md plus the flag's own row
(side-effects column corrected to describe the real precedence).
ResolvePrefersFlagThenEnvironmentThenTerminalDefault's env="0"/terminal
=true case was shown to fail against the prior `== "1"` implementation
(expected false, old code returned true) before the fix landed; the
env="yes" case also failed on the same mutation (old code required the
literal "1", so "yes" fell through to terminal=false instead of enabling).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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