fix: project model and reasoning_effort into Codex CLI args, stop rewriting .codex/config.toml

- Add model_reasoning_effort field to AgentProfile (domain layer)
- Remove model parameter from codex_config_toml, stop rewriting model in TOML
- Pass model and model_reasoning_effort via Codex CLI -c overrides on every exec
- Update CodexExecSession with new_with_policy_and_overrides factory
- Cover new conversation and resume flows with tests

crates/infrastructure/src/session/mod.rs

@@ -625,6 +625,54 @@ mod tests {
         let _ = std::fs::remove_file(&argv);
     }
 
+    #[tokio::test]
+    async fn factory_passes_codex_profile_model_overrides_to_exec_session() {
+        let factory = StructuredSessionFactory::new();
+        let (cmd, argv) = make_recording_fake(&[
+            r#"{"type":"thread.started","thread_id":"cx-new"}"#,
+            r#"{"type":"item.completed","item":{"id":"i0","type":"agent_message","text":"ok"}}"#,
+        ]);
+        let codex = structured_profile(StructuredAdapter::Codex, &cmd)
+            .with_model("gpt-5.4")
+            .with_model_reasoning_effort("medium");
+        let ctx = PreparedContext {
+            content: MarkdownDoc::new("# ctx"),
+            relative_path: "AGENTS.md".to_owned(),
+            project_root: "/project/root".to_owned(),
+        };
+
+        let session = factory
+            .start(
+                &codex,
+                &ctx,
+                &cwd(),
+                &SessionPlan::None,
+                None,
+                &[],
+                None,
+                None,
+            )
+            .await
+            .expect("start Codex ok");
+        let content = drain_final(session.as_ref()).await;
+        assert_eq!(content, "ok");
+
+        let recorded = std::fs::read_to_string(&argv).expect("argv");
+        let args: Vec<&str> = recorded.lines().collect();
+        assert!(
+            args.windows(2).any(|w| w == ["-c", "model=\"gpt-5.4\""]),
+            "factory must relay profile.model to Codex exec overrides, got: {args:?}"
+        );
+        assert!(
+            args.windows(2)
+                .any(|w| w == ["-c", "model_reasoning_effort=\"medium\""]),
+            "factory must relay profile.model_reasoning_effort to Codex exec overrides, got: {args:?}"
+        );
+
+        let _ = std::fs::remove_file(&cmd);
+        let _ = std::fs::remove_file(&argv);
+    }
+
     #[tokio::test]
     async fn factory_resume_seeds_conversation_id() {
         let factory = StructuredSessionFactory::new();
@@ -1774,6 +1822,101 @@ mod tests {
         let _ = std::fs::remove_file(&argv);
     }
 
+    #[tokio::test]
+    async fn codex_new_conversation_command_carries_profile_model_overrides() {
+        let (cmd, argv) = make_recording_fake(&[
+            r#"{"type":"thread.started","thread_id":"cx-new"}"#,
+            r#"{"type":"item.completed","item":{"id":"i0","type":"agent_message","text":"ok"}}"#,
+        ]);
+        let session = CodexExecSession::new_with_policy_and_overrides(
+            SessionId::new_random(),
+            cmd.clone(),
+            "/",
+            None,
+            "workspace-write",
+            vec!["/project/root".to_owned()],
+            Some(true),
+            Some("gpt-5.4".to_owned()),
+            Some("medium".to_owned()),
+            Vec::new(),
+            None,
+            None,
+        );
+        let _ = session.send("salut").await.expect("send ok");
+        let recorded = std::fs::read_to_string(&argv).expect("argv");
+        let args: Vec<&str> = recorded.lines().collect();
+
+        assert_eq!(
+            args,
+            vec![
+                "exec",
+                "--json",
+                "--skip-git-repo-check",
+                "--sandbox",
+                "workspace-write",
+                "--add-dir",
+                "/project/root",
+                "-c",
+                "sandbox_workspace_write.network_access=true",
+                "-c",
+                "model=\"gpt-5.4\"",
+                "-c",
+                "model_reasoning_effort=\"medium\"",
+                "salut",
+            ],
+            "profile model overrides must be passed before the prompt, got: {args:?}"
+        );
+        let _ = std::fs::remove_file(&cmd);
+        let _ = std::fs::remove_file(&argv);
+    }
+
+    #[tokio::test]
+    async fn codex_resume_command_carries_profile_model_overrides_before_resume() {
+        let (cmd, argv) = make_recording_fake(&[
+            r#"{"type":"item.completed","item":{"id":"i0","type":"agent_message","text":"ok"}}"#,
+        ]);
+        let session = CodexExecSession::new_with_policy_and_overrides(
+            SessionId::new_random(),
+            cmd.clone(),
+            "/",
+            Some("cx-id".to_owned()),
+            "workspace-write",
+            vec!["/project/root".to_owned()],
+            None,
+            Some("gpt-5.4".to_owned()),
+            Some("medium".to_owned()),
+            Vec::new(),
+            None,
+            None,
+        );
+        let _ = session.send("vas-y").await.expect("send ok");
+        let recorded = std::fs::read_to_string(&argv).expect("argv");
+        let args: Vec<&str> = recorded.lines().collect();
+
+        assert_eq!(
+            args,
+            vec![
+                "exec",
+                "--json",
+                "--skip-git-repo-check",
+                "--sandbox",
+                "workspace-write",
+                "--add-dir",
+                "/project/root",
+                "-c",
+                "model=\"gpt-5.4\"",
+                "-c",
+                "model_reasoning_effort=\"medium\"",
+                "resume",
+                "cx-id",
+                "vas-y",
+            ],
+            "profile model overrides must precede resume, got: {args:?}"
+        );
+        let _ = std::fs::remove_file(&cmd);
+        let _ = std::fs::remove_file(&argv);
+    }
+
     #[tokio::test]
     async fn codex_read_only_policy_omits_add_dir_and_approval_flag() {
         let (cmd, argv) = make_recording_fake(&[