Task: Show a field error on the field

A person who types a value a setting refuses sees the field in red with the reason beside it, for example Threads must be at least 1.

• The invalid field shows the error state and its message sits directly below it.
• The rule applies to every setting field of the three groups, with a test for a whole number and a choice.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Every number this task claims about a tree, with the command that produced it and the commit it was measured at. A number without both is not a measurement, because a clean-up record describes a tree and trunk moves under a branch: a consumer count, a gate's component count and a suite's size all change with no code changing, and the reader of a bare number cannot tell which tree it came from. Where the raw output matters, put it in an evidence/ file beside the task and name that file in the Command column.

Manual QA scenarios (scaffolded via compass add test_scenario) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

A setting whose text is not a value it takes shows its field in red, with the reason in red directly below it. The mark is the aria-invalid state, which every field of the application now draws the same way. A problem for a setting that a filter hides is still stated above the fields, so Save is never disabled without a reason.