[finding] The shared cron dialect judges no cron syntax at parse time — after #14825 all 9 `CronExpressionInputSchema` sites accept `'not a cron'` green; the verdict is the formula cron-engine's at evaluate time

[zhuangjianguo]

Recorded by the domain:spec seat (session_0174WZTU6XcFcS7g2kykC53i, seat post #6017) during the contract review of PR #15029 (#14825). Bare, for triage; the landing file is packages/spec/src/shared/expression.zod.ts (spec lane) if anything lands at all.

What

packages/spec/src/shared/expression.zod.ts lines 110-113 on origin/main a4e4d2d7 (read 2026-09-03T18:00Z):

export const CronExpressionInputSchema = z.union([
 z.string().min(1).transform((source): Expression => ({ dialect: 'cron', source })),
 ExpressionSchema,
]);

The only parse-time refusals are an empty string, a non-string, and an envelope naming an undeclared dialect. Measured by the #14825 dev (M2, zod 4.4.3, through z.object({ cron: CronExpressionInputSchema.optional() })): '0 9 * * 1-5', the 6-field '0 0 9 * * *' and 'not a cron' all normalize to { dialect: 'cron', source }. No cron parser exists in the spec layer; the syntax verdict (5- or 6-field, or an @yearly…@reboot alias) belongs to the @objectstack/formula cron-engine when the expression is evaluated.

Sites carrying the schema: 8 positions in 7 files before #14825 (api/export.zod.ts, automation/execution.zod.ts, integration/connector.zod.ts, system/cache, system/disaster-recovery twice, system/job, per the #14825 dev's count) plus ai/knowledge-source.zod.ts refresh.cron once PR #15029 lands — 9 in total.

Why it matters

#14825's headline symptom — "an AI author writes a cron, os validate accepts anything, and the failure surfaces at the scheduler" — is closed for that one field by making its describe promise exactly what the parse enforces, not by refusing bad syntax. The symptom stays true at every cron-typed site, by the shared dialect's design. PR #15029's pin file deliberately asserts the non-refusal so that a later change to the shared dialect surfaces there; this card is where that change, if any, gets decided.

Not a decision — three shapes for triage

• (a) A parse-time syntax refinement in spec, on the bare-string arm and on source when dialect === 'cron': a 5- or 6-field grammar plus the @ aliases. Spec cannot import formula (dependency direction), so the grammar would be restated; all 9 sites' pins and describes move in the same PR (Clause ② — accept-set narrowing on 9 published keys).
• (b) Keep the verdict at evaluate time and have os validate or the lint run the cron-engine's parse on cron-typed positions — which needs the D7 ledger to know where they are (ADR-0058 D7 expression conformance ledger discovers only ExpressionInputSchema / SettingsVisibilityInputSchema positions — the 8 CronExpressionInputSchema and 3 TemplateExpressionInputSchema sites sit outside the ratchet, unclassified #15027).
• (c) Leave the parse as it is and record the state in the ADR-0049 ledger as an accepted declared = enforced-by-describe shape, closing this card.

Verified

• Dedup (2026-09-03T18:00Z, search_issues): zero results for parse-time cron syntax validation; positive control returned [finding] CronExpressionInputSchema / TemplateExpressionInputSchema fix the dialect only on the bare-string arm — the envelope arm accepts any declared dialect, so a cron-typed slot parses { dialect: 'cel', source } green #15028, ADR-0058 D7 expression conformance ledger discovers only ExpressionInputSchema / SettingsVisibilityInputSchema positions — the 8 CronExpressionInputSchema and 3 TemplateExpressionInputSchema sites sit outside the ratchet, unclassified #15027 and [finding] KnowledgeSourceSchema.cron is documented as a 5-field cron expression but typed z.string() — the spec's own CronExpressionInputSchema is not used, so 'not a cron' parses green #14825, so the zero is a reading, not a failure mode.
• Adjacent, not duplicates: [finding] CronExpressionInputSchema / TemplateExpressionInputSchema fix the dialect only on the bare-string arm — the envelope arm accepts any declared dialect, so a cron-typed slot parses { dialect: 'cel', source } green #15028 (the envelope arm accepts any declared dialect), ADR-0058 D7 expression conformance ledger discovers only ExpressionInputSchema / SettingsVisibilityInputSchema positions — the 8 CronExpressionInputSchema and 3 TemplateExpressionInputSchema sites sit outside the ratchet, unclassified #15027 (the D7 conformance ledger's discovery excludes Cron/Template-typed sites).

Refs: #14825 · PR #15029 · #15028 · #15027 · ADR-0049 · ADR-0058.