expression gate: a date-arithmetic verdict in a flow condition still says the value "silently evaluates to null", though the run fails #30016

domain:server#6 · os-support-ai · session_01WGufzibcN9oHa8kDbTTnL5

Filing gate: ① the gate tells an author something untrue about run time, at a named location. Found by the #29959 dev (report 6623979276) and confirmed by the contract review of PR #30015 (6624166953). ⛔ Not a claim. No grade: triage sets it.
Business reason: #29926 and #29959 made a flow condition's type verdicts say what really happens: the run fails. The date-arithmetic verdict was left out. It still tells a flow author their condition "silently evaluates to null", but dag-traversal.ts evaluateCondition throws on a non-ok evaluation for every flow. The author is told the flow will carry on when it will not.
Reader who acts: domain:server, packages/formula/src/validate.ts (typeSoundnessIssue, the date-arith branch) and packages/lint/src/validate-expressions.ts (the flow sites' outcome).
Dedupe (open and closed): date arithmetic flow condition "evaluates to null". The nearest are #29959 (open, PR #30015: the text and boolean overloads only; it rightly does not extend the date verdicts), #29904 (closed) and #1928 (closed, the original cel-js null guardrail). None covers the date branch's sentence on flow sites. New.

What happens

The date-arith branch of typeSoundnessIssue serves one sentence, "silently evaluates to null", whatever the scope and outcome. On a flow condition (start, edge, decision) the run fails instead.

What to fix

Give the date branch the same per-site outcome the text and boolean overloads get since PR #29953 / PR #30015: the run-fails wording (and grading) on record-triggered flows, and the run-may-fail wording elsewhere. Keep the record-scoped validation-rule sentence where it is true. Measure first, after PR #30015 lands, because it moves the same code. Pins: one per flow site, plus a record-scoped control. Ablate once.