refactor(desktop): share mention send error presentation

Extract the identical authorization-aware error presentation from both send failure paths so normal formatter output respects the file-size ratchet.

Co-authored-by: Larry <627498bd4bd1f281a16431e3c6cce3b5c25b6692798c78672298aefbf2f8f8b5@buzz.block.builderlab.xyz>
Signed-off-by: Logan Johnson <loganj@squareup.com>

desktop/src/features/messages/ui/useMentionSendFlow.helpers.test.mjs

@@ -3,11 +3,31 @@ import test from "node:test";
 
 import {
   formatMessageSendError,
+  formatMentionSendError,
   getErrorMessage,
   mergeMentionRecipients,
   mentionRevalidationOptions,
 } from "./useMentionSendFlow.helpers.ts";
 
+import { AgentMentionAuthorizationError } from "../lib/agentMentionRevalidation.ts";
+
+test("mention send errors preserve authorization guidance and generic failure details", () => {
+  const denied = new AgentMentionAuthorizationError();
+  assert.equal(formatMentionSendError(denied), denied.message);
+  assert.equal(
+    formatMentionSendError(new Error("relay rejected")),
+    "Message failed to send: relay rejected",
+  );
+  assert.equal(
+    formatMentionSendError("upload rejected"),
+    "Message failed to send: upload rejected",
+  );
+  assert.equal(
+    formatMentionSendError({}),
+    "Message failed to send: Unknown error",
+  );
+});
+
 test("formatMessageSendError preserves the publication failure", () => {
   assert.equal(
     formatMessageSendError(new Error("relay rejected voice note")),

desktop/src/features/messages/ui/useMentionSendFlow.helpers.ts

@@ -1,4 +1,7 @@
-import type { MentionRevalidationOptions } from "@/features/messages/lib/agentMentionRevalidation";
+import {
+  AgentMentionAuthorizationError,
+  type MentionRevalidationOptions,
+} from "@/features/messages/lib/agentMentionRevalidation";
 import type { ManagedAgent } from "@/shared/api/types";
 import {
   type ImetaMedia,
@@ -110,6 +113,13 @@ export function formatMessageSendError(error: unknown) {
   return `Message failed to send: ${getErrorMessage(error, "Unknown error")}`;
 }
 
+/** Preserve actionable authorization errors without the generic send-failure prefix. */
+export function formatMentionSendError(error: unknown) {
+  return error instanceof AgentMentionAuthorizationError
+    ? error.message
+    : formatMessageSendError(error);
+}
+
 export function uniqueNormalizedPubkeys(pubkeys: Iterable<string>) {
   return [...new Set([...pubkeys].map(normalizePubkey))].filter(Boolean);
 }

desktop/src/features/messages/ui/useMentionSendFlow.ts

@@ -31,7 +31,7 @@ import type { ManagedAgent } from "@/shared/api/types";
 import { normalizePubkey, truncatePubkey } from "@/shared/lib/pubkey";
 import { buildCustomEmojiTags } from "@/shared/lib/customEmojiTags";
 import {
-  formatMessageSendError,
+  formatMentionSendError,
   getErrorMessage,
   mentionRevalidationOptions,
   withoutInvitingRecipients,
@@ -44,7 +44,6 @@ import {
   uniqueNormalizedPubkeys,
 } from "./useMentionSendFlow.helpers";
 import { buildAgentAddressMentionTags } from "@/features/messages/lib/agentAddressMention.mjs";
-import { AgentMentionAuthorizationError } from "@/features/messages/lib/agentMentionRevalidation";
 import type { UseMentionSendFlowOptions } from "./useMentionSendFlow.types";
 
 export function useMentionSendFlow({
@@ -650,11 +649,7 @@ export function useMentionSendFlow({
                 await finishSend(uploaded, signal);
               } catch (error) {
                 restoreComposerAfterFailure();
-                toast.error(
-                  error instanceof AgentMentionAuthorizationError
-                    ? error.message
-                    : formatMessageSendError(error),
-                );
+                toast.error(formatMentionSendError(error));
               } finally {
                 settleUpload();
               }
@@ -682,11 +677,7 @@ export function useMentionSendFlow({
             await finishSend([]);
           } catch (error) {
             restoreComposerAfterFailure();
-            toast.error(
-              error instanceof AgentMentionAuthorizationError
-                ? error.message
-                : formatMessageSendError(error),
-            );
+            toast.error(formatMentionSendError(error));
           }
         }
       } catch (error) {