fix: align reply threading refs

src/auto-reply/reply/reply-reference.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+
+import { createReplyReferencePlanner } from "./reply-reference.js";
+
+describe("createReplyReferencePlanner", () => {
+  it("disables references when mode is off", () => {
+    const planner = createReplyReferencePlanner({
+      replyToMode: "off",
+      startId: "parent",
+    });
+    expect(planner.use()).toBeUndefined();
+    expect(planner.hasReplied()).toBe(false);
+  });
+
+  it("uses startId once when mode is first", () => {
+    const planner = createReplyReferencePlanner({
+      replyToMode: "first",
+      startId: "parent",
+    });
+    expect(planner.use()).toBe("parent");
+    expect(planner.hasReplied()).toBe(true);
+    planner.markSent();
+    expect(planner.use()).toBeUndefined();
+  });
+
+  it("returns startId for every call when mode is all", () => {
+    const planner = createReplyReferencePlanner({
+      replyToMode: "all",
+      startId: "parent",
+    });
+    expect(planner.use()).toBe("parent");
+    expect(planner.use()).toBe("parent");
+  });
+
+  it("prefers existing thread id regardless of mode", () => {
+    const planner = createReplyReferencePlanner({
+      replyToMode: "off",
+      existingId: "thread-1",
+      startId: "parent",
+    });
+    expect(planner.use()).toBe("thread-1");
+    expect(planner.hasReplied()).toBe(true);
+  });
+
+  it("honors allowReference=false", () => {
+    const planner = createReplyReferencePlanner({
+      replyToMode: "all",
+      startId: "parent",
+      allowReference: false,
+    });
+    expect(planner.use()).toBeUndefined();
+    expect(planner.hasReplied()).toBe(false);
+    planner.markSent();
+    expect(planner.hasReplied()).toBe(true);
+  });
+});

src/auto-reply/reply/reply-reference.ts

@@ -0,0 +1,56 @@
+import type { ReplyToMode } from "../../config/types.js";
+
+export type ReplyReferencePlanner = {
+  /** Returns the effective reply/thread id for the next send and updates state. */
+  use(): string | undefined;
+  /** Mark that a reply was sent (needed when no reference is used). */
+  markSent(): void;
+  /** Whether a reply has been sent in this flow. */
+  hasReplied(): boolean;
+};
+
+export function createReplyReferencePlanner(options: {
+  replyToMode: ReplyToMode;
+  /** Existing thread/reference id (always used when present). */
+  existingId?: string;
+  /** Id to start a new thread/reference when allowed (e.g., parent message id). */
+  startId?: string;
+  /** Disable reply references entirely (e.g., when posting inside a new thread). */
+  allowReference?: boolean;
+  /** Seed the planner with prior reply state. */
+  hasReplied?: boolean;
+}): ReplyReferencePlanner {
+  let hasReplied = options.hasReplied ?? false;
+  const allowReference = options.allowReference !== false;
+  const existingId = options.existingId?.trim();
+  const startId = options.startId?.trim();
+
+  const use = (): string | undefined => {
+    if (!allowReference) return undefined;
+    if (existingId) {
+      hasReplied = true;
+      return existingId;
+    }
+    if (!startId) return undefined;
+    if (options.replyToMode === "off") return undefined;
+    if (options.replyToMode === "all") {
+      hasReplied = true;
+      return startId;
+    }
+    if (!hasReplied) {
+      hasReplied = true;
+      return startId;
+    }
+    return undefined;
+  };
+
+  const markSent = () => {
+    hasReplied = true;
+  };
+
+  return {
+    use,
+    markSent,
+    hasReplied: () => hasReplied,
+  };
+}