diff --git a/‎.changeset/22161-lint-slice-3-one-line.md‎
Lines changed: 18 additions & 0 deletions b/‎.changeset/22161-lint-slice-3-one-line.md‎
Lines changed: 18 additions & 0 deletions
diff --git a/‎packages/lint/src/rule-explanations.ts‎
Lines changed: 302 additions & 0 deletions b/‎packages/lint/src/rule-explanations.ts‎
Lines changed: 302 additions & 0 deletions
diff --git a/‎packages/lint/src/validate-action-body-writes.test.ts‎
Lines changed: 80 additions & 16 deletions b/‎packages/lint/src/validate-action-body-writes.test.ts‎
Lines changed: 80 additions & 16 deletions
diff --git a/‎packages/lint/src/validate-action-body-writes.ts‎
Lines changed: 20 additions & 27 deletions b/‎packages/lint/src/validate-action-body-writes.ts‎
Lines changed: 20 additions & 27 deletions
@@ -0,0 +1,18 @@
+---
+"@objectstack/lint": patch
+---
+
+fix(lint): 14 more author-time findings print one verdict line, and `os explain <rule-id>` carries their reasoning
+
+Clause-②: no
+
+- **Shorter verdicts.** Each finding of these 14 rule ids now prints a `message` of one verdict sentence. Every finding the rules' own test suites fire, and the CLI suite's handler-hook variants, is at most 200 characters; before, the longest of each ran from 212 to 792 characters. The ids:
+  - hook bodies: `hook-body-write-unknown-field`, `hook-body-write-unprovisioned-anchor`, `hook-body-source-unparseable`;
+  - action bodies: `action-body-write-unknown-field`, `action-body-write-unprovisioned-anchor`, `action-record-write-discarded`, `action-body-source-unparseable`;
+  - flow nodes: `flow-node-write-unknown-field`, `flow-node-write-unprovisioned-anchor`;
+  - readonly writes: `flow-update-readonly-field`, `flow-update-readonly-when-field`, `hook-api-update-readonly-field`, `hook-api-update-readonly-when-field`, `action-api-update-readonly-when-field`.
+
+  The three write surfaces now share one wording per question: an undeclared field ends on "so the write is refused (INVALID_FIELD / 400)", an unprovisioned anchor reads "'FIELD' is an injected column with no storage on external object 'OBJECT', so … can never land", an unparseable hook or action body reads "L2 body did not parse (…), so writes in its unread part go unchecked", and a readonly write says it is "silently stripped" (a `readonlyWhen` field "where its predicate is TRUE"). The values the author wrote still close each verdict — the field, the object, the `ctx.api` call, the run identity — so a verdict over a long name grows with it, and a hook lowered from an inline `handler` keeps its " (judged on the metadata body lowered from the inline handler)" suffix. 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 14 ids**, for example `os explain hook-body-write-unknown-field`. It prints the reasoning the verdicts no longer carry: how each write channel reaches the engine's declared-field door and what the refusal takes down with it, why a write to an unprovisioned anchor on an external object passes the validator and never lands, what a partially parsed body leaves unchecked, why an action's `ctx.record` is never written back, and which readonly strip a system context waives and which it does not. The paragraphs the three surfaces share 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 14 ids, and so does the unknown-id error's `Rules with an explanation:` line. `RULE_EXPLANATIONS` in `@objectstack/lint` gains the 14 entries.
+- **Where the new text prints.** On the CLI, `os validate`, `os build` (and `os compile`, which `os dev` runs on every compile), `os lint`, `os verify` and `os init`'s scaffold check print the new `message` on the text face, and `os validate --json` and `os build --json` carry it in their `warnings` and author-time `issues`. At the runtime publish gate (Studio, REST `/meta`, MCP), a `flow` write carries the four flow ids: `flow-node-write-unknown-field` and `flow-update-readonly-field` are errors, so the 422 issue's `message` and the refusal log line under `OS_ALLOW_UNLINTED_METADATA_WRITES` change; `flow-node-write-unprovisioned-anchor` and `flow-update-readonly-when-field` are warnings, so the `message` in the 2xx response's `advisories` and the deduped `[Protocol] authoring advisory` server log line change. Each issue's `hint` is unchanged.
+- **Never at the runtime gate:** the ten hook and action ids. A `hook` or `action` write does not dispatch these rules (they parse authored JavaScript, which the publish path never loads), and a `flow` write's snapshot carries no hook or action body for them to read; they speak only on the CLI doors above.
@@ -2,7 +2,7 @@
 
 import { describe, it, expect } from 'vitest';
 import {
-  validateActionBodyWrites,
+  validateActionBodyWrites as validateActionBodyWritesUnrecorded,
   ACTION_BODY_WRITE_PATTERNS,
   ACTION_BODY_WRITE_PATTERN_IDS,
   ACTION_RECORD_WRITE_PATTERNS,
@@ -18,6 +18,30 @@ import {
   HOOK_BODY_WRITE_PATTERNS,
   IMPLICIT_FIELDS,
 } from './validate-hook-body-writes.js';
+import { explainRule } from './rule-explanations.js';
+
+// [#22161] Each finding of the rule ids this file's rule shortened is one
+// verdict sentence; the reasoning it used to carry is the id's `os explain`
+// entry. Every call below records what it fired, and the last case in this
+// file holds each recorded verdict of those ids to one line of at most 200
+// characters — so the pin covers every firing variant this suite exercises,
+// not a chosen few. Run the whole file: that case reads what the cases above
+// fired.
+const SHORTENED_RULE_IDS: readonly string[] = [
+  ACTION_BODY_WRITE_UNPROVISIONED_ANCHOR,
+  ACTION_BODY_WRITE_UNKNOWN_FIELD,
+  ACTION_RECORD_WRITE_DISCARDED,
+  ACTION_BODY_SOURCE_UNPARSEABLE,
+];
+const firedShortened: Array<{ rule: string; message: string }> = [];
+const validateActionBodyWrites: typeof validateActionBodyWritesUnrecorded = (...args) => {
+  const findings = validateActionBodyWritesUnrecorded(...args);
+  for (const f of findings) if (SHORTENED_RULE_IDS.includes(f.rule)) firedShortened.push(f);
+  return findings;
+};
+
+/** The `os explain` text of `rule`, one string. */
+const explanationOf = (rule: string): string => explainRule(rule)?.paragraphs.join('\n') ?? '';
 
 // Target objects: array-shaped and map-shaped `fields`, so both authoring
 // shapes are resolved.
@@ -163,7 +187,7 @@ describe('validateActionBodyWrites — ctx.api writes', () => {
     expect(findings[0].path).toBe('actions[0].body.source');
     expect(findings[0].message).toContain('discont_total');
     expect(findings[0].message).toContain('crm_deal');
-    expect(findings[0].message).toContain('INVALID_FIELD / 400, identically on every driver');
+    expect(findings[0].message).toContain('INVALID_FIELD / 400');
     expect(findings[0].hint).toContain("'discount_total'");
   });
 
@@ -176,24 +200,30 @@ describe('validateActionBodyWrites — ctx.api writes', () => {
   // The old text promised a driver-level error on SQL and a persisted stray
   // key on schemaless — neither happens on this path, and has not since
   // #8682/#8738 put the declared-field door ahead of any statement.
+  //
+  // [#22161] The verdict names the refusal; the rest of the measured account
+  // is `os explain action-body-write-unknown-field`, so it is pinned there.
   it('states the measured refusal — INVALID_FIELD / 400 on every driver — and no driver split', () => {
     const [finding] = validateActionBodyWrites(
       stackWith("await ctx.api.object('crm_deal').update({ discont_total: 0 });"),
     );
+    const explanation = explanationOf(ACTION_BODY_WRITE_UNKNOWN_FIELD);
 
     expect(finding.message).toContain('INVALID_FIELD / 400');
-    expect(finding.message).toContain('identically on every driver');
-    expect(finding.message).toContain('before any statement is built');
+    expect(explanation).toContain('identically on every driver');
+    expect(explanation).toContain('before any statement is built');
     // The reason the door — not a driver — is what answers.
-    expect(finding.message).toContain('ordinary CALLER write');
-    // The action-side blast radius, the one word that differs from the hook
-    // sibling's sentence. Pinned so a future sweep cannot flatten the two.
-    expect(finding.message).toContain('fails the action');
-
-    expect(finding.message).not.toMatch(/driver-level error/);
-    expect(finding.message).not.toMatch(/schemaless/);
-    expect(finding.message).not.toMatch(/is persisted/);
-    expect(finding.message).not.toMatch(/write-path validator skips/);
+    expect(explanation).toContain('ordinary CALLER write');
+    // The action-side blast radius, the one sentence that differs from the
+    // hook sibling's explanation. Pinned so a future sweep cannot flatten the two.
+    expect(explanation).toContain('fails the action');
+
+    for (const text of [finding.message, explanation]) {
+      expect(text).not.toMatch(/driver-level error/);
+      expect(text).not.toMatch(/schemaless/);
+      expect(text).not.toMatch(/is persisted/);
+      expect(text).not.toMatch(/write-path validator skips/);
+    }
   });
 
   it('checks insert/update payloads (argument 0) and updateById at argument 1', () => {
@@ -203,7 +233,7 @@ describe('validateActionBodyWrites — ctx.api writes', () => {
           "await ctx.api.object('crm_deal').updateById(ctx.recordId, { stag: 'won' });",
       ),
     );
-    expect(findings.map((f) => f.message.match(/writing '(\w+)'/)?.[1])).toEqual(['emial', 'stag']);
+    expect(findings.map((f) => f.message.match(/writing undeclared field '(\w+)'/)?.[1])).toEqual(['emial', 'stag']);
     expect(findings[0].message).toContain("ctx.api.object('crm_contact').insert");
     expect(findings[1].message).toContain('updateById');
   });
@@ -313,7 +343,10 @@ describe('validateActionBodyWrites — discarded ctx.record writes (#4345)', ()
     expect(findings[0].where).toBe('action "close_deal" › body');
     expect(findings[0].path).toBe('actions[0].body.source');
     expect(findings[0].message).toContain('ctx.record.stage');
-    expect(findings[0].message).toContain("The snapshot stays read-only by design: an action's write channel is ctx.api.");
+    // [#22161] Why the snapshot is not a write surface is the id's `os explain` text.
+    expect(explanationOf(ACTION_RECORD_WRITE_DISCARDED)).toContain(
+      "The snapshot stays read-only by design: an action's write channel is `ctx.api`.",
+    );
     expect(findings[0].hint).toContain('updateById');
   });
 
@@ -528,7 +561,7 @@ describe('[#8663] validateActionBodyWrites — unprovisioned anchor writes', ()
     expect(findings[0].where).toBe('action "stamp_owner" › body');
     expect(findings[0].path).toBe('actions[0].body.source');
     expect(findings[0].message).toContain("'owner_id'");
-    expect(findings[0].message).toContain('external object (ADR-0015)');
+    expect(findings[0].message).toContain("external object 'wh_order'");
     expect(findings[0].message).toContain('can never land');
   });
 
@@ -592,3 +625,34 @@ describe('an unparseable action body is reported, not scored clean (#10653)', ()
     }
   });
 });
+
+describe('[#22161] one-line verdicts — the rule ids this file shortened', () => {
+  it('every verdict the cases above fired for those ids is one line of at most 200 characters', () => {
+    // The coverage control first: each shortened id fired at least once, so
+    // the shape assertion below cannot pass over an empty record.
+    expect([...new Set(firedShortened.map((f) => f.rule))].sort()).toEqual([...SHORTENED_RULE_IDS].sort());
+    for (const f of firedShortened) {
+      expect(f.message, f.rule).not.toContain('\n');
+      expect(f.message.length, `${f.rule}: ${f.message}`).toBeLessThanOrEqual(200);
+    }
+  });
+
+  // What each verdict stopped saying, which `os explain RULE_ID` now prints.
+  const MOVED: Record<string, readonly string[]> = {
+    [ACTION_BODY_WRITE_UNPROVISIONED_ANCHOR]: ['external object', 'ADR-0015', 'PAST the write-path validator', 'no such column', 'schemaless remote'],
+    [ACTION_BODY_WRITE_UNKNOWN_FIELD]: ['scoped handle on the running engine', 'ordinary CALLER write', 'before any statement is built', 'fails the action'],
+    [ACTION_RECORD_WRITE_DISCARDED]: ['whether or not NAME is a declared field', 'read-only by design', 'provably dead'],
+    [ACTION_BODY_SOURCE_UNPARSEABLE]: ['partially recovered', 'judged by no rule', 'action-api-update-readonly-when-field'],
+  };
+
+  it('covers exactly the shortened ids', () => {
+    expect(Object.keys(MOVED).sort()).toEqual([...SHORTENED_RULE_IDS].sort());
+  });
+
+  it.each([...SHORTENED_RULE_IDS])('`os explain %s` carries what its verdict no longer says', (rule) => {
+    const explanation = explainRule(rule);
+    expect(explanation, `no \`os explain ${rule}\` entry`).toBeDefined();
+    const text = explanation!.paragraphs.join('\n');
+    for (const fact of MOVED[rule]) expect(text, `${rule} explanation names ${fact}`).toContain(fact);
+  });
+});
@@ -83,18 +83,16 @@
 
 import { findClosestMatches, formatSuggestion } from '@objectstack/spec/shared';
 
-import { describeParseFailure, PARSE_FAILURE_HINT } from './checked-parse.js';
-import {
-  indexUnprovisionedAnchors,
-  unprovisionedAnchorCause,
-  unprovisionedAnchorHint,
-} from './system-fields.js';
+import { PARSE_FAILURE_HINT } from './checked-parse.js';
+import { indexUnprovisionedAnchors, unprovisionedAnchorHint } from './system-fields.js';
 import {
+  bodyParseFailureVerdict,
   extractHookBodyWriteSet,
   indexObjectFields,
   judgeableFieldsOf,
   IMPLICIT_FIELDS,
-  unprovisionedAnchorWriteConsequence,
+  undeclaredApiWriteVerdict,
+  unprovisionedAnchorWriteVerdict,
   HOOK_BODY_WRITE_PATTERNS,
   type BodyWritePatternExclusion,
   type HookBodyWritePattern,
@@ -341,9 +339,8 @@ export function validateActionBodyWrites(stack: AnyRec): ActionBodyWriteFinding[
         rule: ACTION_BODY_SOURCE_UNPARSEABLE,
         where,
         path: site.path,
-        message:
-          `L2 body did not parse (${describeParseFailure(parseFailure)}), so its write set was read from a ` +
-          `partially recovered tree — an undeclared field write in the unread part is not reported.`,
+        // [#22161] The hook twin's sentence, from the one function both use.
+        message: bodyParseFailureVerdict(parseFailure),
         hint: PARSE_FAILURE_HINT,
       });
     }
@@ -365,11 +362,13 @@ export function validateActionBodyWrites(stack: AnyRec): ActionBodyWriteFinding[
           rule: ACTION_RECORD_WRITE_DISCARDED,
           where,
           path: site.path,
+          // [#22161] One verdict sentence; that the snapshot is read-only by
+          // design whether or not the field is declared, and why only a
+          // provably dead write is reported, is
+          // `os explain action-record-write-discarded`.
           message:
-            `body assigns ctx.record.${w.field}, but an action's ctx.record is a plain snapshot the runtime ` +
-            `never writes back — the action returns success and the assignment is discarded, whether or not ` +
-            `'${w.field}' is a declared field. The snapshot stays read-only by design: an action's ` +
-            `write channel is ctx.api.`,
+            `body assigns ctx.record.${w.field}, but an action's ctx.record is a snapshot the runtime never ` +
+            `writes back, so the assignment is discarded while the action returns success`,
           hint:
             `To persist it, write through the API: ctx.api.object('<object>').updateById(ctx.recordId, ` +
             `{ ${w.field}: … }). Reported only because ctx.record is never passed anywhere in this body — ` +
@@ -408,9 +407,7 @@ export function validateActionBodyWrites(stack: AnyRec): ActionBodyWriteFinding[
           rule: ACTION_BODY_WRITE_UNPROVISIONED_ANCHOR,
           where,
           path: site.path,
-          message:
-            `body calls ctx.api.object('${w.object}').${w.method ?? 'update'}(…) writing '${w.field}', and ` +
-            `${unprovisionedAnchorCause(w.object, w.field)} — ${unprovisionedAnchorWriteConsequence()}`,
+          message: unprovisionedAnchorWriteVerdict(w.object, w.field, `the body's ${w.method ?? 'update'}(…) write`),
           hint: unprovisionedAnchorHint(w.object, w.field),
         });
         continue;
@@ -422,16 +419,12 @@ export function validateActionBodyWrites(stack: AnyRec): ActionBodyWriteFinding[
         rule: ACTION_BODY_WRITE_UNKNOWN_FIELD,
         where,
         path: site.path,
-        message:
-          `body calls ctx.api.object('${w.object}').${w.method ?? 'update'}(…) writing '${w.field}', but ` +
-          // [#13858] Same door, same measurement as the hook sibling — ctx.api
-          // is a ScopedContext over the running engine, so this payload is
-          // CALLER-supplied and #8682/#8738 refuse it before any driver.
-          `object '${w.object}' declares no such field. ctx.api is a scoped handle on the running ` +
-          `engine, so the payload arrives as an ordinary CALLER write and the declared-field door ` +
-          `REFUSES it at run time — INVALID_FIELD / 400, identically on every driver, before ` +
-          `any statement is built. The write lands nothing, and the refusal escapes the body and ` +
-          `fails the action.`,
+        // [#13858] Same door, same measurement as the hook sibling — ctx.api
+        // is a ScopedContext over the running engine, so this payload is
+        // CALLER-supplied and #8682/#8738 refuse it before any driver.
+        // [#22161] The hook sibling's verdict, from the one function both use;
+        // the reasoning is `os explain action-body-write-unknown-field`.
+        message: undeclaredApiWriteVerdict(w.object, w.method ?? 'update', w.field),
         hint: fixHint(w.field, [...known]),
       });
     }