fix(lint): one-line verdicts for the flow-trigger, react-page, dataset-measure and validation-rule compile rules; os explain RULE_ID carries their reasoning

.changeset/22161-lint-slice-5-one-line.md

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+---
+"@objectstack/lint": patch
+---
+
+fix(lint): the flow-trigger, react-page, dataset-measure and validation-rule findings print one verdict line, and `os explain <rule-id>` carries their reasoning
+
+Clause-②: no
+
+- **Shorter verdicts.** Each finding of these 15 rule ids now prints a `message` of one verdict sentence. Every finding the rules' own test suites and the runtime publish gate's suites fire is at most 194 characters; before, the longest of each ran from 211 to 1,049 characters. The ids:
+  - flow triggers (`flows[].nodes[]` start node): `flow-time-relative-descriptor-invalid`, `flow-time-relative-descriptor-unroutable`, `flow-trigger-unroutable`, `flow-api-trigger-secret-missing`, `flow-trigger-unknown-event`;
+  - react pages (`pages[].source`): `react-chart-drilldown-invalid`, `react-chart-aggregate-invalid`, `react-chart-field-unprovisioned`, `react-block-needs-record-context`, `react-page-source-unparseable`;
+  - dataset and cube members: `measure-aggregate-field-type-refused`, `dimension-json-stored-field-refused`;
+  - object validation rules: `validation-rule-json-schema-uncompilable`, `validation-rule-regex-uncompilable`, `validation-rule-json-schema-unknown-format`.
+
+  A verdict no longer repeats what the finding's `where` and `path` already name: the validation rule and its object, the JSON Pointer of a `format`, the measure or dimension name, the source of an uncompilable `regex` (the `fix:` line still quotes it). A refusal the verdict quotes is quoted to its verdict. `TimeRelativeTriggerSchema`'s refusal of a descriptor is quoted for ONE issue (an unrecognized key first) and the rest are counted, `(and N more)`; ajv's metaschema refusal is quoted to its first violation, with the rest counted; a `@objectstack/spec` unknown-key refusal is quoted to the key and the schema's rename (`Did you mean …?`), without the wrong-layer prescription and the history sentence that follow it; and when no form of an `<ObjectChart aggregate>` `groupBy` union matches, the verdict keeps the forms whose complaint is about the value's content. A measure or dimension over a column its join chain reaches names a `joined object` (it read "(reached through this dataset's join chain)"). The `fix` (the CLI's `fix:` line, the runtime issue's `hint`), every rule id, severity and `path`, and what each rule accepts or refuses are unchanged. A tool that matched the old message text should match on `rule` and `path` instead.
+- **`os explain <rule-id>` takes these 15 ids**, for example `os explain flow-trigger-unroutable`. It prints the reasoning the verdicts no longer carry: the engine's trigger routing chain, the record-trigger token grammar and the time-relative routing predicate, what nothing reports at run time, and where the publish gate refuses the flow; the inbound api secret (ADR-0041) and why the engine refuses to register a flow without one; the write path's fail-open skip of a rule whose `regex` or `schema` does not compile, the runtime's ajv environment, and what ajv does with an unregistered `format` name; each aggregate's accepted field types (the `AGGREGATE_FIELD_TYPE_COMPATIBILITY` rows, written out), what a JSON-stored column is, and why analytics refuses to group by one; how a forwarded `<ObjectChart drillDown>` or `aggregate` refusal is quoted and which keys the schema answers with a prescription instead of a rename (`schedule` and `runAs` on a time-relative descriptor, `drilldown`, `mode`, `report`, `view` and `sort` on a drill block, five aggregate and two `groupBy` keys); what an unprovisioned anchor is; why a `record:*` block renders empty on a react page; and why an unparseable react source is a warning. Paragraphs shared across ids are one text, printed under every id they explain. The `rule:` line under each of these findings now ends with `` — `os explain <rule-id>` for … ``. The no-argument listing and its `--json` `rules` array list the 15 ids, and so does the unknown-id error's `Rules with an explanation:` line. `RULE_EXPLANATIONS` in `@objectstack/lint` gains the 15 entries.
+- **Where the new text prints.** On the CLI, all 15 ids: `os validate`, `os build` (and `os compile`, which `os dev` runs on every compile), `os lint`, `os verify`, and the scaffold check `os init` and `os generate` run print the new `message` on the text face, and `os validate --json` and `os build --json` carry it in their `errors` and author-time `issues`. At the runtime publish gate (Studio, REST `/meta`, MCP): a `flow` write carries the five flow ids (all errors, refusing an active flow's publish), a `dataset` write the two dataset ids, and an `object` write the three validation-rule ids — the 422 issue's `message` and the refusal log line under `OS_ALLOW_UNLINTED_METADATA_WRITES` change. Each issue's `hint` is unchanged.
+- **Never at the runtime gate:** the five `react-*` ids. Their rule runs at that door only for a flow write, whose snapshot carries no pages, so they speak only on the CLI doors above.