test(ui): unit-test comment-reply helpers

Cover buildReplyExcerpt (whitespace collapse, exact-length no-truncate,
over-length clamp+flag, boundary trim), buildOptimisticReplyTo (identity
mirror + null normalization), and formatReplyAuthorName (agent name, unknown
agent fallback, System, You). Satisfies the PR quality gate's test requirement
and locks the excerpt contract shared with the server snapshot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ui/src/lib/comment-reply.test.ts

@@ -0,0 +1,116 @@
+import type { Agent, IssueComment } from "@paperclipai/shared";
+import { describe, expect, it } from "vitest";
+import {
+  REPLY_EXCERPT_MAX_LENGTH,
+  buildOptimisticReplyTo,
+  buildReplyExcerpt,
+  formatReplyAuthorName,
+} from "./comment-reply";
+
+function makeComment(overrides: Partial<IssueComment> = {}): IssueComment {
+  const now = new Date("2026-04-06T13:00:00.000Z");
+  return {
+    id: "comment-1",
+    companyId: "company-1",
+    issueId: "issue-1",
+    authorType: "agent",
+    authorAgentId: "agent-1",
+    authorUserId: null,
+    body: "Hello there",
+    presentation: null,
+    metadata: null,
+    createdAt: now,
+    updatedAt: now,
+    ...overrides,
+  };
+}
+
+describe("buildReplyExcerpt", () => {
+  it("collapses runs of whitespace and newlines into a single line", () => {
+    const { excerpt, truncated } = buildReplyExcerpt("  line one\n\n  line   two\t");
+    expect(excerpt).toBe("line one line two");
+    expect(truncated).toBe(false);
+  });
+
+  it("does not truncate a body at exactly the max length", () => {
+    const body = "a".repeat(REPLY_EXCERPT_MAX_LENGTH);
+    const { excerpt, truncated } = buildReplyExcerpt(body);
+    expect(excerpt).toHaveLength(REPLY_EXCERPT_MAX_LENGTH);
+    expect(truncated).toBe(false);
+  });
+
+  it("clamps and flags a body longer than the max length", () => {
+    const body = "b".repeat(REPLY_EXCERPT_MAX_LENGTH + 50);
+    const { excerpt, truncated } = buildReplyExcerpt(body);
+    expect(excerpt).toHaveLength(REPLY_EXCERPT_MAX_LENGTH);
+    expect(truncated).toBe(true);
+  });
+
+  it("trims trailing whitespace left at the clamp boundary", () => {
+    const body = `${"word ".repeat(60)}`; // well over the limit, boundary lands on a space
+    const { excerpt } = buildReplyExcerpt(body);
+    expect(excerpt.length).toBeLessThanOrEqual(REPLY_EXCERPT_MAX_LENGTH);
+    expect(excerpt).toBe(excerpt.trimEnd());
+  });
+});
+
+describe("buildOptimisticReplyTo", () => {
+  it("mirrors the target's identity and a clamped excerpt", () => {
+    const target = makeComment({
+      id: "comment-src",
+      authorType: "agent",
+      authorAgentId: "agent-7",
+      authorUserId: null,
+      body: "c".repeat(REPLY_EXCERPT_MAX_LENGTH + 10),
+    });
+    const snapshot = buildOptimisticReplyTo(target);
+    expect(snapshot).toEqual({
+      commentId: "comment-src",
+      authorType: "agent",
+      authorAgentId: "agent-7",
+      authorUserId: null,
+      excerpt: "c".repeat(REPLY_EXCERPT_MAX_LENGTH),
+      excerptTruncated: true,
+    });
+  });
+
+  it("normalizes undefined author ids to null for a user comment", () => {
+    const target = makeComment({
+      id: "comment-user",
+      authorType: "user",
+      authorAgentId: undefined as unknown as string | null,
+      authorUserId: "user-9",
+      body: "short",
+    });
+    const snapshot = buildOptimisticReplyTo(target);
+    expect(snapshot.authorAgentId).toBeNull();
+    expect(snapshot.authorUserId).toBe("user-9");
+    expect(snapshot.excerptTruncated).toBe(false);
+  });
+});
+
+describe("formatReplyAuthorName", () => {
+  const agentMap = new Map<string, Agent>([
+    ["agent-1", { id: "agent-1", name: "CodexCoder" } as Agent],
+  ]);
+
+  it("uses the agent name when the target is an agent in the map", () => {
+    expect(
+      formatReplyAuthorName({ authorType: "agent", authorAgentId: "agent-1" }, agentMap),
+    ).toBe("CodexCoder");
+  });
+
+  it("falls back to a short agent id when the agent is unknown", () => {
+    expect(
+      formatReplyAuthorName({ authorType: "agent", authorAgentId: "agent-abcdef123" }, agentMap),
+    ).toBe("agent-ab");
+  });
+
+  it("labels system authors as System", () => {
+    expect(formatReplyAuthorName({ authorType: "system", authorAgentId: null })).toBe("System");
+  });
+
+  it("labels user authors as You", () => {
+    expect(formatReplyAuthorName({ authorType: "user", authorAgentId: null })).toBe("You");
+  });
+});