feat(src/bridge/linear): attribute comments to the Discord author

Pass createAsUser (display name) and displayIconUrl (avatar) on comments so
they render as the external Discord author once the bridge uses an OAuth app
token. Personal API keys ignore these fields, so the author name stays in the
comment body for now.

Author: phorcys420

src/bridge/linear/api.ts

@@ -91,8 +91,20 @@ export async function upsertThreadAttachment(
   });
 }
 
-export async function addComment(issueId: string, body: string): Promise<void> {
-  await linear().createComment({ issueId, body });
+export async function addComment(
+  issueId: string,
+  body: string,
+  author?: { name: string; iconUrl?: string },
+): Promise<void> {
+  await linear().createComment({
+    issueId,
+    body,
+    // Attributes the comment to an external (non-Linear) author. Only takes
+    // effect when authenticated as an OAuth application; ignored for personal
+    // API keys.
+    createAsUser: author?.name,
+    displayIconUrl: author?.iconUrl,
+  });
 }
 
 // Moves an issue to the first workflow state of the given type in the team.

src/bridge/linear/index.ts

@@ -46,10 +46,15 @@ export class LinearMirror {
     if (!content) return;
 
     const name = message.member?.displayName ?? message.author.username;
-    const author = isTeam ? `${name} (Coder team)` : name;
+    const iconUrl =
+      message.member?.displayAvatarURL() ?? message.author.displayAvatarURL();
+    const label = isTeam ? `${name} (Coder team)` : name;
 
     const issueId = await this.ensureIssue();
-    await linear.addComment(issueId, `**${author}**\n\n${content}`);
+    await linear.addComment(issueId, `**${label}**\n\n${content}`, {
+      name,
+      iconUrl,
+    });
   }
 
   // Refreshes the attachment metadata and labels, and moves the issue's