Discord: fix /codex_resume identity resolution in brand-new threads

In brand-new Discord threads, the slash interaction can set ctx.from to the
slash user identity (e.g. "slash:user-id") while the real channel target is
in ctx.to. The previous ctx.from ?? ctx.to expression normalized a slash
identity to undefined, causing toConversationTargetFromCommand() to return
null and /cas_resume to fail on the first attempt.

Fix: when ctx.from starts with "slash:", use ctx.to as the channel source
instead. The existing behavior for established channels (ctx.from holds the
channel identity) is unchanged.

Adds a regression test covering the brand-new-thread scenario.

Fixes #30

Author: huntharo

src/controller.test.ts

@@ -320,6 +320,33 @@ describe("Discord controller flows", () => {
     );
   });
 
+  it("resolves channel identity from ctx.to when ctx.from is a slash identity in a new Discord thread", async () => {
+    // Regression test for brand-new Discord threads where the slash interaction
+    // places the slash user identity in ctx.from and the channel target in ctx.to.
+    const { controller, sendComponentMessage } = await createControllerHarness();
+
+    const reply = await controller.handleCommand(
+      "cas_resume",
+      buildDiscordCommandContext({
+        from: "slash:user-1",
+        to: "discord:channel:chan-1",
+      }),
+    );
+
+    expect(reply).toEqual({
+      text: "Sent a Codex thread picker to this Discord conversation.",
+    });
+    expect(sendComponentMessage).toHaveBeenCalledWith(
+      "channel:chan-1",
+      expect.objectContaining({
+        text: expect.stringContaining("Showing recent Codex sessions"),
+      }),
+      expect.objectContaining({
+        accountId: "default",
+      }),
+    );
+  });
+
   it("sends Discord model pickers directly instead of returning Telegram buttons", async () => {
     const { controller, sendComponentMessage } = await createControllerHarness();
     await (controller as any).store.upsertBinding({

src/controller.ts

@@ -271,7 +271,12 @@ function toConversationTargetFromCommand(ctx: PluginCommandContext): Conversatio
     };
   }
   if (isDiscordChannel(ctx.channel)) {
-    const conversationId = normalizeDiscordConversationId(ctx.from ?? ctx.to);
+    // In brand-new Discord threads, the slash interaction may place the slash
+    // user identity in ctx.from (e.g. "slash:user-id") while ctx.to holds the
+    // real channel target. Prefer ctx.to when ctx.from is a slash identity so
+    // /cas_resume resolves to the correct channel from the first attempt.
+    const sourceId = ctx.from?.startsWith("slash:") ? ctx.to : (ctx.from ?? ctx.to);
+    const conversationId = normalizeDiscordConversationId(sourceId);
     if (!conversationId) {
       return null;
     }