chore: import upstream snapshot with attribution

tests/unit/executor-github-prefill-sanitize.test.ts

@@ -0,0 +1,119 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { GithubExecutor } from "../../open-sse/executors/github.ts";
+
+// GitHub Copilot's /chat/completions endpoint rejects a conversation that ends with an
+// assistant message: "This model does not support assistant message prefill. The
+// conversation must end with a user message." Anthropic clients (e.g. newest Claude
+// Desktop) send a trailing assistant turn as a prefill seed — the Anthropic API honors
+// it, but Copilot 400s. GithubExecutor.dropTrailingAssistantPrefill() strips the
+// trailing assistant message(s) before dispatch, scoped to the github executor only.
+// Port of 9router#2143 (author: Manuel <baslr@users.noreply.github.com>).
+
+test("dropTrailingAssistantPrefill drops a single trailing assistant message", () => {
+  const executor = new GithubExecutor();
+  const messages = [
+    { role: "user", content: "Hi" },
+    { role: "assistant", content: "Here is the answer:" },
+  ];
+
+  const out = executor.dropTrailingAssistantPrefill(messages);
+
+  assert.equal(out.length, 1);
+  assert.equal(out[0].role, "user");
+});
+
+test("dropTrailingAssistantPrefill drops multiple consecutive trailing assistant messages", () => {
+  const executor = new GithubExecutor();
+  const messages = [
+    { role: "user", content: "Hi" },
+    { role: "assistant", content: "one" },
+    { role: "assistant", content: "two" },
+  ];
+
+  const out = executor.dropTrailingAssistantPrefill(messages);
+
+  assert.equal(out.length, 1);
+  assert.equal(out[0].role, "user");
+});
+
+test("dropTrailingAssistantPrefill is a no-op (same reference) when the conversation ends with a user message", () => {
+  const executor = new GithubExecutor();
+  const messages = [
+    { role: "user", content: "Hi" },
+    { role: "assistant", content: "Hello" },
+    { role: "user", content: "More" },
+  ];
+
+  const out = executor.dropTrailingAssistantPrefill(messages);
+
+  assert.equal(out, messages, "must return the same array reference when nothing changes");
+  assert.equal(out.length, 3);
+});
+
+test("dropTrailingAssistantPrefill is a no-op when the conversation ends with a tool message", () => {
+  const executor = new GithubExecutor();
+  const messages = [
+    { role: "user", content: "Hi" },
+    { role: "assistant", content: null, tool_calls: [{ id: "x" }] },
+    { role: "tool", tool_call_id: "x", content: "result" },
+  ];
+
+  const out = executor.dropTrailingAssistantPrefill(messages);
+
+  assert.equal(out, messages, "must return the same array reference when nothing changes");
+  assert.equal(out.length, 3);
+  assert.equal(out[2].role, "tool");
+});
+
+test("dropTrailingAssistantPrefill never empties an assistant-only conversation", () => {
+  const executor = new GithubExecutor();
+  const messages = [{ role: "assistant", content: "only" }];
+
+  const out = executor.dropTrailingAssistantPrefill(messages);
+
+  assert.equal(out.length, 1, "must keep at least one message");
+  assert.equal(out[0].role, "assistant");
+});
+
+test("dropTrailingAssistantPrefill is null/empty safe", () => {
+  const executor = new GithubExecutor();
+
+  assert.deepEqual(executor.dropTrailingAssistantPrefill([]), []);
+  assert.equal(executor.dropTrailingAssistantPrefill(undefined), undefined);
+  assert.equal(executor.dropTrailingAssistantPrefill(null), null);
+});
+
+test("GithubExecutor.transformRequest drops the trailing assistant prefill end-to-end", () => {
+  const executor = new GithubExecutor();
+  const body = {
+    model: "claude-sonnet-4.6",
+    messages: [
+      { role: "user", content: "Hi" },
+      { role: "assistant", content: "Here is the answer:" },
+    ],
+  };
+
+  const out = executor.transformRequest("claude-sonnet-4.6", body, false, {});
+
+  assert.equal(out.messages.length, 1);
+  assert.equal(out.messages[0].role, "user");
+});
+
+test("GithubExecutor.transformRequest leaves a user-terminated conversation untouched end-to-end", () => {
+  const executor = new GithubExecutor();
+  const body = {
+    model: "claude-sonnet-4.6",
+    messages: [
+      { role: "user", content: "Hi" },
+      { role: "assistant", content: "Hello" },
+      { role: "user", content: "More" },
+    ],
+  };
+
+  const out = executor.transformRequest("claude-sonnet-4.6", body, false, {});
+
+  assert.equal(out.messages.length, 3);
+  assert.equal(out.messages[2].role, "user");
+});