Add exec output-schema parameter (#4079)

Adds structured output to `exec` via the `--structured-output`
parameter.

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

@@ -1,5 +1,6 @@
 // Aggregates all former standalone integration tests as modules.
 mod apply_patch;
 mod common;
+mod output_schema;
 mod resume;
 mod sandbox;

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

@@ -0,0 +1,76 @@
+#![cfg(not(target_os = "windows"))]
+#![allow(clippy::expect_used, clippy::unwrap_used)]
+
+use assert_cmd::prelude::*;
+use core_test_support::responses;
+use serde_json::Value;
+use std::process::Command;
+use tempfile::TempDir;
+use wiremock::matchers::any;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_includes_output_schema_in_request() -> anyhow::Result<()> {
+    let home = TempDir::new()?;
+    let workspace = TempDir::new()?;
+
+    let schema_contents = serde_json::json!({
+        "type": "object",
+        "properties": {
+            "answer": { "type": "string" }
+        },
+        "required": ["answer"],
+        "additionalProperties": false
+    });
+    let schema_path = workspace.path().join("schema.json");
+    std::fs::write(&schema_path, serde_json::to_vec_pretty(&schema_contents)?)?;
+    let expected_schema: Value = schema_contents;
+
+    let server = responses::start_mock_server().await;
+    let body = responses::sse(vec![
+        serde_json::json!({
+            "type": "response.created",
+            "response": {"id": "resp1"}
+        }),
+        responses::ev_assistant_message("m1", "fixture hello"),
+        responses::ev_completed("resp1"),
+    ]);
+    responses::mount_sse_once(&server, any(), body).await;
+
+    Command::cargo_bin("codex-exec")?
+        .current_dir(workspace.path())
+        .env("CODEX_HOME", home.path())
+        .env("OPENAI_API_KEY", "dummy")
+        .env("OPENAI_BASE_URL", format!("{}/v1", server.uri()))
+        .arg("--skip-git-repo-check")
+        .arg("-C")
+        .arg(workspace.path())
+        .arg("--output-schema")
+        .arg(&schema_path)
+        .arg("-m")
+        .arg("gpt-5")
+        .arg("tell me a joke")
+        .assert()
+        .success();
+
+    let requests = server
+        .received_requests()
+        .await
+        .expect("failed to capture requests");
+    assert_eq!(requests.len(), 1, "expected exactly one request");
+    let payload: Value = serde_json::from_slice(&requests[0].body)?;
+    let text = payload.get("text").expect("request missing text field");
+    let format = text
+        .get("format")
+        .expect("request missing text.format field");
+    assert_eq!(
+        format,
+        &serde_json::json!({
+            "name": "codex_output_schema",
+            "type": "json_schema",
+            "strict": true,
+            "schema": expected_schema,
+        })
+    );
+
+    Ok(())
+}