[exec] Clean up apply-patch tests (#2648)

## Summary
These tests were getting a bit unwieldy, and they're starting to become
load-bearing. Let's clean them up, and get them working solidly so we
can easily expand this harness with new tests.

## Test Plan
- [x] Tests continue to pass

codex-rs/exec/tests/suite/common.rs

@@ -0,0 +1,73 @@
+// this file is only used for e2e tests which are currently disabled on windows
+#![cfg(not(target_os = "windows"))]
+#![allow(clippy::expect_used)]
+
+use anyhow::Context;
+use assert_cmd::prelude::*;
+use core_test_support::load_sse_fixture_with_id_from_str;
+use std::path::Path;
+use std::process::Command;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering;
+use wiremock::Mock;
+use wiremock::MockServer;
+use wiremock::matchers::method;
+use wiremock::matchers::path;
+
+use wiremock::Respond;
+
+struct SeqResponder {
+    num_calls: AtomicUsize,
+    responses: Vec<String>,
+}
+
+impl Respond for SeqResponder {
+    fn respond(&self, _: &wiremock::Request) -> wiremock::ResponseTemplate {
+        let call_num = self.num_calls.fetch_add(1, Ordering::SeqCst);
+        match self.responses.get(call_num) {
+            Some(body) => wiremock::ResponseTemplate::new(200)
+                .insert_header("content-type", "text/event-stream")
+                .set_body_raw(
+                    load_sse_fixture_with_id_from_str(body, &format!("request_{}", call_num)),
+                    "text/event-stream",
+                ),
+            None => panic!("no response for {call_num}"),
+        }
+    }
+}
+
+/// Helper function to run an E2E test of a codex-exec call. Starts a wiremock
+/// server, and returns the response_streams in order for each api call. Runs
+/// the codex-exec command with the wiremock server as the model server.
+pub(crate) async fn run_e2e_exec_test(cwd: &Path, response_streams: Vec<String>) {
+    let server = MockServer::start().await;
+
+    let num_calls = response_streams.len();
+    let seq_responder = SeqResponder {
+        num_calls: AtomicUsize::new(0),
+        responses: response_streams,
+    };
+
+    Mock::given(method("POST"))
+        .and(path("/v1/responses"))
+        .respond_with(seq_responder)
+        .expect(num_calls as u64)
+        .mount(&server)
+        .await;
+
+    let cwd = cwd.to_path_buf();
+    let uri = server.uri();
+    Command::cargo_bin("codex-exec")
+        .context("should find binary for codex-exec")
+        .expect("should find binary for codex-exec")
+        .current_dir(cwd.clone())
+        .env("CODEX_HOME", cwd.clone())
+        .env("OPENAI_API_KEY", "dummy")
+        .env("OPENAI_BASE_URL", format!("{}/v1", uri))
+        .arg("--skip-git-repo-check")
+        .arg("-s")
+        .arg("danger-full-access")
+        .arg("foo")
+        .assert()
+        .success();
+}