Conditional and Expression script triggers gain an optional `mode` field
in their TriggerConfiguration JSON:
- OnTrue (default): unchanged edge/per-change firing. An absent mode field
parses as OnTrue, so every existing trigger config behaves identically.
- WhileTrue: fires on the false->true edge, then re-fires on a periodic
timer while the condition holds; stops on the true->false edge. The
re-fire cadence is the script's MinTimeBetweenRuns; with none configured
the trigger degrades to a single edge fire and logs a warning.
ScriptActor tracks condition truth state and manages a dedicated
"whiletrue-trigger" timer. ScriptTriggerConfigCodec and ScriptTriggerEditor
round-trip the mode and expose an OnTrue/WhileTrue selector for the two
trigger kinds. Design: docs/plans/2026-05-18-whiletrue-trigger-mode-design.md
Tests: 7 ScriptActor runtime tests (edge fire, timer re-fire, stop,
re-arm, no-MinTimeBetweenRuns degrade, OnTrue regressions) + 14 codec /
editor tests. SiteRuntime suite 206 green, CentralUI suite 295 green.
