feat: add conversation context builder

tests/moderation/conversationContext.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from "vitest";
+import { buildConversationPromptMessages } from "../../src/moderation/conversationContext";
+import type { MessageRecord } from "../../src/moderation/types";
+
+function message(
+  id: string,
+  content: string,
+  created_at: number,
+): MessageRecord {
+  return {
+    id,
+    guild_id: "g1",
+    channel_id: "c1",
+    thread_id: null,
+    user_id: `u-${id}`,
+    username: `user-${id}`,
+    avatar_url: null,
+    content,
+    edited_content: null,
+    created_at,
+    edited_at: null,
+    deleted_at: null,
+    type: "text",
+    metadata: null,
+    ai_status: "pending",
+  };
+}
+
+describe("buildConversationPromptMessages", () => {
+  it("marks target messages and keeps chronological order", () => {
+    const lines = buildConversationPromptMessages({
+      contextBefore: [message("a", "hello", 1)],
+      targets: [message("b", "bad?", 2)],
+      maxTokens: 1000,
+    });
+
+    expect(lines).toContain(
+      "[context] id=a time=1970-01-01T00:00:00.001Z user=user-a: hello",
+    );
+    expect(lines).toContain(
+      "[target] id=b time=1970-01-01T00:00:00.002Z user=user-b: bad?",
+    );
+
+    const indexA = lines.findIndex((line) => line.includes("id=a"));
+    const indexB = lines.findIndex((line) => line.includes("id=b"));
+    expect(indexA).toBeLessThan(indexB);
+  });
+
+  it("uses edited content when present", () => {
+    const target = message("b", "original", 2);
+    target.edited_content = "edited";
+
+    const lines = buildConversationPromptMessages({
+      contextBefore: [],
+      targets: [target],
+      maxTokens: 1000,
+    });
+
+    expect(lines.some((line) => line.includes("edited"))).toBe(true);
+    expect(lines.some((line) => line.includes("original"))).toBe(false);
+  });
+});