@@ -0,0 +1,17 @@
+---
+'@objectstack/service-automation': patch
+'@objectstack/runtime': patch
+---
+
+fix(service-automation,runtime): a flow whose data node is refused answers its caller with the refusal structured — `details.innerRefusal` and the producer-marked `userMessage` on every door's `400 FLOW_FAILED` — beside an unchanged `message`
+
+Clause-②: yes (widening)
+Metadata-protocol: none
+
+Ruling B′ on #24914 (the maintainer's 「同意」, decision batch #379 item 5), the emission half of the contract `@objectstack/spec` declared in #24996. A record save the platform refuses reaches a record form as `code`, `message` and the producer-marked `userMessage`; the same refusal met by a flow's data node used to be flattened into one string (`Node 'ID' failed: create_record(OBJECT) failed: …`), so a screen flow could only show its user that developer text.
+
+- **`service-automation`.** The catch arms of `get_record`, `create_record`, `update_record` and `delete_record` read the refusal off the thrown error: the producer-marked `userMessage` (through `declaredUserMessage`) and, for a throw that declared a 4xx answer, `{ code, message }` with `code` in the WIRE spelling the data door answers for the same throw — `UNIQUE_VIOLATION` for a unique refusal, `VALIDATION_FAILED`, `PERMISSION_DENIED`, or the member an app hook's declared status names. `NodeExecutionResult` gains the two optional members, and the engine carries them from the failing node to `AutomationResult.userMessage` / `.innerRefusal` on `execute()`'s failure exit, the `resumeInternal` stranded exit and the retry exits. A fault (no declared answer, or a declared 5xx) carries neither member; nothing is read from message text.
+- **`runtime`.** The trigger, resume, `/actions` and declared-endpoint doors build their `400 FLOW_FAILED` details through one builder typed as `FlowFailureDetailsSchema` (`errorMessage?`, `summary?`, `innerRefusal?`) and put the run's `userMessage` at the envelope's top level (`ApiErrorSchema.userMessage`). The MCP `resume_run` bridge carries both as the REST resume door serves them. `DomainHandlerDeps.error` gains an optional fourth argument, `extra: { userMessage? }`, the declared slot the doors use; a call without it builds the envelope it always built.
+- **Unchanged.** Every `error` / `message` text, byte for byte — the node's, the engine's prefix, the stored run, approvals and each door's wording. The in-flow `$error.code` keeps the engine's in-process `DUPLICATE_RECORD`. `error.code` stays `FLOW_FAILED`, and `AutomationResult.code` stays the closed union.
+
+**For consumers.** A flow runner can render a refused run the way a record form renders a refused save: the top-level `userMessage` when present, then `details.innerRefusal`, then `message`. A client that does not read the new members keeps its current behaviour. A container that rewords a child's failure into its own (`try_catch` without a catch region, `subflow`) does not forward the members yet; the run then carries none.
@@ -42,6 +42,8 @@ import { relationConditionSites } from '@objectstack/core';
 // result, and a second definition of the rule is what let the doors diverge.
 import {
     classifyFlowRefusal,
+    flowFailureDetails,
+    flowFailureEnvelope,
     flowIsUnknown,
     flowNotFoundMessage,
     FLOW_NOT_FOUND_STATUS,
@@ -50,7 +52,7 @@ import {
 // Who may START a flow by name — the one rule the trigger door, this door and
 // the declared endpoint share (the maintainer's ruling, letters B and A).
 import { ELEVATED_START_REFUSAL, refusesElevatedSelfTriggeredStart } from './flow-start-admission.js';
-import type { FlowRunSummary } from '@objectstack/spec/automation';
+import type { FlowFailureDetails } from '@objectstack/spec/api';
 // [#5138] The ONE 404 envelope a single-record path answers. Imported rather
 // than re-spelled so `callData`'s ObjectQL fallback and the protocol service it
 // falls back FROM cannot disagree about what "this id names no row" looks like.
@@ -1044,22 +1046,17 @@ const FLOW_ACTION_REFUSAL_BRAND = Symbol.for('objectstack.runtime.flowActionRefu
 
 /**
  * The run artefacts a failed flow dispatch carries beside its status and code
- * — EXACTLY the two fields the trigger door ships in `error.details` on its
- * own `400 FLOW_FAILED` arm (`domains/automation.ts`), same names, same
- * source (`AutomationResult.errorMessage` / `.summary`). The #9585 ruling
- * capped this at those two keys; ruling B′ on #24914 (decision batch #379
- * item 5) relaxes the cap by exactly one, `innerRefusal`, and the spec now
- * declares the three-key set once for every flow door as
- * `FlowFailureDetailsSchema` (`@objectstack/spec/api`). Carrying that third
- * key is #24914's emission half and is not done here yet; any key beyond the
- * three is a contract widening neither ruling covers.
+ * — EXACTLY the fields the trigger door ships in `error.details` on its own
+ * `400 FLOW_FAILED` arm (`domains/automation.ts`), same names, same source,
+ * built by the same `flowFailureDetails` (`./flow-dispatch-status.ts`). The
+ * #9585 ruling capped this at two keys (`errorMessage`, `summary`); ruling B′
+ * on #24914 (decision batch #379 item 5) relaxes the cap by exactly one,
+ * `innerRefusal`, and the spec declares the three-key set once for every flow
+ * door as `FlowFailureDetailsSchema` (`@objectstack/spec/api`). This type IS
+ * that declaration, so a key beyond the three — a contract widening neither
+ * ruling covers — fails the build rather than reaching the wire.
  */
-export interface FlowActionRunDetails {
-    /** The flow AUTHOR's own failure text (`flow.errorMessage`). */
-    errorMessage?: string;
-    /** The run's per-node accounting — WHICH node failed (#4354). */
-    summary?: FlowRunSummary;
-}
+export type FlowActionRunDetails = FlowFailureDetails;
 
 /**
  * [#9585] The typed refusal carrier for a flow ACTION that ran and failed.
@@ -1090,19 +1087,31 @@ export class FlowActionRefusal extends Error {
     readonly status: number;
     /** ADR-0112 `error.code` — registered, never minted here. */
     readonly code: FlowRefusalCode;
-    /** The two run artefacts the door carries into `error.details`. */
+    /** The run artefacts the door carries into `error.details`. */
     readonly runDetails: FlowActionRunDetails;
+    /**
+     * [#24914, ruling B′] The producer-marked END-USER text of the refusal the
+     * run's node met (`AutomationResult.userMessage`), absent when the run
+     * carries none. A FIELD of the thrown error on purpose: it is the channel
+     * `declaredUserMessage` (`@objectstack/types`) reads on every boundary, so
+     * the `/actions` handler relays it to the envelope's top level and a door
+     * that does not recognise this carrier still reads it off the throw,
+     * exactly as it reads an app hook's own marking.
+     */
+    readonly userMessage?: string;
 
     constructor(
         message: string,
         refusal: { status: number; code: FlowRefusalCode },
         runDetails: FlowActionRunDetails,
+        userMessage?: string,
     ) {
         super(message);
         this.name = 'FlowActionRefusal';
         this.status = refusal.status;
         this.code = refusal.code;
         this.runDetails = runDetails;
+        if (userMessage !== undefined) this.userMessage = userMessage;
         (this as Record<PropertyKey, unknown>)[FLOW_ACTION_REFUSAL_BRAND] = true;
     }
 }
@@ -1290,13 +1299,17 @@ export async function dispatchFlowAction(deps: ActionExecutionDeps,
             // there would be this door inventing run evidence for a run that
             // never started, which is why the two rows below stay plain
             // throws.
+            //
+            // [#24914, ruling B′] Built by the trigger door's own builder
+            // (`flowFailureDetails`), so the `innerRefusal` a node's data call
+            // met rides here too, and the producer-marked `userMessage` rides
+            // the carrier for the handler to put at the envelope's top level.
+            // The message keeps this door's wording byte for byte.
             throw new FlowActionRefusal(
                 `Flow '${action.target}' failed: ${result.error ?? 'unknown error'}`,
                 refusal,
-                {
-                    ...(result.errorMessage !== undefined ? { errorMessage: result.errorMessage } : {}),
-                    ...(result.summary !== undefined ? { summary: result.summary } : {}),
-                },
+                flowFailureDetails(result),
+                flowFailureEnvelope(result)?.userMessage,
             );
         }
         const err: any = new Error(refusal.message);
 
@@ -309,8 +309,19 @@ export interface DomainHandlerDeps {
      * `error.code`). `error.code` is the semantic string: pass yours as
      * `details.code` and it is promoted into the field, otherwise one is derived
      * from the status. See `./error-envelope.ts`.
+     *
+     * `extra` carries the declared SIBLINGS of `code` / `message` a domain may
+     * put on the envelope — today exactly one, the producer-marked
+     * `userMessage` (`ApiErrorSchema.userMessage`, `@objectstack/spec/api`):
+     * end-user text that never replaces `message`. It is the slot ruling B′ on
+     * #24914 names for the four flow doors, which relay the refusal a flow's
+     * data node met (`AutomationResult.userMessage`) the way the data door
+     * relays a record save's. Closed on purpose: a sibling the spec does not
+     * declare has no slot here, so a domain cannot put an undeclared key on
+     * the envelope through it. Omit it (or leave `userMessage` absent) and the
+     * envelope is byte-identical to the three-argument call.
      */
-    error(message: string, httpStatus?: number, details?: any): { status: number; body: any };
+    error(message: string, httpStatus?: number, details?: any, extra?: { userMessage?: string }): { status: number; body: any };
     /** Standard ROUTE_NOT_FOUND envelope (404 + discovery hint). */
     routeNotFound(route: string): { status: number; body: any };
     /**
 
@@ -824,9 +824,16 @@ export async function handleActionsRequest(deps: DomainHandlerDeps, path: string
                 // other thrower (#8016 / #9106 — its closed `details` list is
                 // deliberate, not a gap this branch works around).
                 if (actionExec.isFlowActionRefusal(err)) {
+                    // [#24914, ruling B′] `runDetails` now carries the
+                    // `innerRefusal` a node's data call met (the declared third
+                    // key), and the carrier's producer-marked `userMessage`
+                    // goes to the envelope's top level through the deps slot.
                     return {
                         handled: true,
-                        response: deps.error(err.message, err.status, { code: err.code, ...err.runDetails }),
+                        response: deps.error(
+                            err.message, err.status, { code: err.code, ...err.runDetails },
+                            err.userMessage !== undefined ? { userMessage: err.userMessage } : undefined,
+                        ),
                     };
                 }
                 throw err;
 
@@ -47,6 +47,8 @@ import { capabilityUnavailable } from './unavailable.js';
 // [#9446] The ONE #9378 status table, now shared with the `/actions` door.
 import {
     classifyFlowRefusal,
+    flowFailureDetails,
+    flowFailureEnvelope,
     flowIsUnknown,
     flowNotFoundMessage,
     isPausedRun,
@@ -2033,15 +2035,20 @@ async function respondToFlowTrigger(
         // that happened. A never-dispatched refusal has no author failure text
         // and no node log to point at, so emitting either there would be this
         // door inventing run evidence for a run that never started.
-        const runDetails = refusal.code === 'FLOW_FAILED'
-            ? {
-                ...(result.errorMessage !== undefined ? { errorMessage: result.errorMessage } : {}),
-                ...(result.summary !== undefined ? { summary: result.summary } : {}),
-            }
-            : {};
+        //
+        // [#24914, ruling B′] Built by the one shared builder, typed as
+        // `FlowFailureDetailsSchema`: `errorMessage` / `summary` as before, and
+        // the `innerRefusal` a node's data call met; the producer-marked
+        // `userMessage` rides the envelope's top level, beside an unchanged
+        // `message`.
+        const failed = refusal.code === 'FLOW_FAILED';
+        const runDetails = failed ? flowFailureDetails(result) : {};
         return {
             handled: true,
-            response: deps.error(refusal.message, refusal.status, { code: refusal.code, ...runDetails }),
+            response: deps.error(
+                refusal.message, refusal.status, { code: refusal.code, ...runDetails },
+                failed ? flowFailureEnvelope(result) : undefined,
+            ),
         };
     }
     // [#9510] THE THIRD STATE, answered deliberately. A run that dispatched and
@@ -2252,6 +2259,14 @@ export interface ResumeRefusal {
     message: string;
     status: number;
     details: { code: string } & Record<string, unknown>;
+    /**
+     * [#24914, ruling B′] The envelope's declared top-level siblings — the
+     * producer-marked `userMessage` of the refusal the run's node met, set on
+     * the `FLOW_FAILED` row only and only when the engine result carries one.
+     * Passed as `DomainHandlerDeps.error`'s `extra` by both doors this table
+     * serves.
+     */
+    extra?: { userMessage: string };
 }
 
 /**
@@ -2349,15 +2364,21 @@ export async function classifyResumeResult(
     // code it matched, so the builder promotes it and never derives one.
     if (code !== undefined && row) return { message: result.error ?? row.fallback, status: row.status, details: { code } };
     const verdict = await resumeFailureDetails(deps, automationService, runId, result);
+    // [#24914, ruling B′] The run's artefacts through the shared builder
+    // (`FlowFailureDetailsSchema`: `errorMessage` / `summary` / `innerRefusal`),
+    // the verdict beside them in the same object, and the producer-marked
+    // `userMessage` at the envelope's top level. The screen-flow leg — a write
+    // behind a screen, refused after the pause was consumed — answers HERE.
+    const extra = flowFailureEnvelope(result);
     return {
         message: result.error ?? 'Flow run failed',
         status: 400,
         details: {
             code: 'FLOW_FAILED',
-            ...(result.errorMessage !== undefined ? { errorMessage: result.errorMessage } : {}),
-            ...(result.summary !== undefined ? { summary: result.summary } : {}),
+            ...flowFailureDetails(result),
             ...verdict,
         },
+        ...(extra !== undefined ? { extra } : {}),
     };
 }
 
@@ -3326,7 +3347,7 @@ export async function handleAutomationRequest(deps: DomainHandlerDeps, path: str
                 // it answers what it answers, is documented there.
                 const refusal = await classifyResumeResult(deps, automationService, parts[2], result);
                 if (refusal) {
-                    return { handled: true, response: deps.error(refusal.message, refusal.status, refusal.details) };
+                    return { handled: true, response: deps.error(refusal.message, refusal.status, refusal.details, refusal.extra) };
                 }
                 return { handled: true, response: deps.success(result) };
             }
 
@@ -808,13 +808,21 @@ function resumeDoorError(
     message: string,
     httpStatus: number,
     details?: Record<string, unknown>,
+    extra?: { userMessage?: string },
 ): Error {
-    const response = deps.error(message, httpStatus, details);
-    const envelope = (response?.body as { error?: { code?: unknown; message?: unknown; details?: unknown } } | undefined)?.error;
+    const response = deps.error(message, httpStatus, details, extra);
+    const envelope = (response?.body as {
+        error?: { code?: unknown; message?: unknown; details?: unknown; userMessage?: unknown };
+    } | undefined)?.error;
     return Object.assign(new Error(typeof envelope?.message === 'string' ? envelope.message : message), {
         code: typeof envelope?.code === 'string' ? envelope.code : undefined,
         status: response?.status ?? httpStatus,
         ...(envelope?.details !== undefined ? { details: envelope.details } : {}),
+        // [#24914, ruling B′] The producer-marked end-user text, carried onto
+        // the thrown error as the `userMessage` field every boundary reads
+        // through `declaredUserMessage` — exactly what the REST door put at the
+        // envelope's top level, never folded into `message`.
+        ...(typeof envelope?.userMessage === 'string' ? { userMessage: envelope.userMessage } : {}),
     });
 }
 
@@ -1001,7 +1009,7 @@ export async function resumeActionRun(
     if (values !== undefined) signal.variables = values;
     const result = await automation.resume(runId, signal);
     const refusal = await classifyResumeResult(deps, automation, runId, result);
-    if (refusal) throw resumeDoorError(deps, refusal.message, refusal.status, refusal.details);
+    if (refusal) throw resumeDoorError(deps, refusal.message, refusal.status, refusal.details, refusal.extra);
     return { ok: true, action: action.name, objectName, ...(recordId ? { recordId } : {}), result: result ?? null };
 }
 
 
@@ -56,6 +56,8 @@ import { validationFailure } from './validation-failure.js';
 import { buildAutomationContext } from './domains/automation.js';
 import {
     classifyFlowRefusal,
+    flowFailureDetails,
+    flowFailureEnvelope,
     flowIsUnknown,
     flowNotFoundMessage,
     FLOW_NOT_FOUND_STATUS,
@@ -585,17 +587,21 @@ async function executeFlow(
         // failure text nor a node log to point at. Byte-identical to the
         // trigger door's details (`domains/automation.ts`), because #5040 §4
         // makes that route's answer this seam's contract.
-        const runDetails = refusal.code === 'FLOW_FAILED'
-            ? {
-                ...(result.errorMessage !== undefined ? { errorMessage: result.errorMessage } : {}),
-                ...(result.summary !== undefined ? { summary: result.summary } : {}),
-            }
-            : {};
+        //
+        // [#24914, ruling B′] The trigger door's own builder, so the
+        // `innerRefusal` a node's data call met rides here as it does there,
+        // and the producer-marked `userMessage` takes the envelope's declared
+        // top-level slot (`extra`, `ApiErrorSchema.userMessage`) — authored
+        // end-user text, so the message's leak guard does not apply to it.
+        const failed = refusal.code === 'FLOW_FAILED';
+        const runDetails = failed ? flowFailureDetails(result) : {};
+        const extra = failed ? flowFailureEnvelope(result) : undefined;
         return apiErrorResponse({
             message: sanitizeMessage(refusal.message, refusal.status),
             httpStatus: refusal.status,
             code: refusal.code,
             ...(Object.keys(runDetails).length > 0 ? { details: runDetails } : {}),
+            ...(extra !== undefined ? { extra } : {}),
         });
     }