feat: add support for -c/--config to override individual config items (#1137)

This PR introduces support for `-c`/`--config` so users can override
individual config values on the command line using `--config
name=value`. Example:

```
codex --config model=o4-mini
```

Making it possible to set arbitrary config values on the command line
results in a more flexible configuration scheme and makes it easier to
provide single-line examples that can be copy-pasted from documentation.

Effectively, it means there are four levels of configuration for some
values:

- Default value (e.g., `model` currently defaults to `o4-mini`)
- Value in `config.toml` (e.g., user could override the default to be
`model = "o3"` in their `config.toml`)
- Specifying `-c` or `--config` to override `model` (e.g., user can
include `-c model=o3` in their list of args to Codex)
- If available, a config-specific flag can be used, which takes
precedence over `-c` (e.g., user can specify `--model o3` in their list
of args to Codex)

Now that it is possible to specify anything that could be configured in
`config.toml` on the command line using `-c`, we do not need to have a
custom flag for every possible config option (which can clutter the
output of `--help`). To that end, as part of this PR, we drop support
for the `--disable-response-storage` flag, as users can now specify `-c
disable_response_storage=true` to get the equivalent functionality.

Under the hood, this works by loading the `config.toml` into a
`toml::Value`. Then for each `key=value`, we create a small synthetic
TOML file with `value` so that we can run the TOML parser to get the
equivalent `toml::Value`. We then parse `key` to determine the point in
the original `toml::Value` to do the insert/replace. Once all of the
overrides from `-c` args have been applied, the `toml::Value` is
deserialized into a `ConfigToml` and then the `ConfigOverrides` are
applied, as before.

codex-rs/tui/src/cli.rs

@@ -1,5 +1,6 @@
 use clap::Parser;
 use codex_common::ApprovalModeCliArg;
+use codex_common::CliConfigOverrides;
 use codex_common::SandboxPermissionOption;
 use std::path::PathBuf;
 
@@ -40,7 +41,6 @@ pub struct Cli {
     #[arg(long = "skip-git-repo-check", default_value_t = false)]
     pub skip_git_repo_check: bool,
 
-    /// Disable server‑side response storage (sends the full conversation context with every request)
-    #[arg(long = "disable-response-storage", default_value_t = false)]
-    pub disable_response_storage: bool,
+    #[clap(skip)]
+    pub config_overrides: CliConfigOverrides,
 }

codex-rs/tui/src/lib.rs

@@ -54,18 +54,23 @@ pub fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> std::io::
             model: cli.model.clone(),
             approval_policy,
             sandbox_policy,
-            disable_response_storage: if cli.disable_response_storage {
-                Some(true)
-            } else {
-                None
-            },
             cwd: cli.cwd.clone().map(|p| p.canonicalize().unwrap_or(p)),
             model_provider: None,
             config_profile: cli.config_profile.clone(),
             codex_linux_sandbox_exe,
         };
+        // Parse `-c` overrides from the CLI.
+        let cli_kv_overrides = match cli.config_overrides.parse_overrides() {
+            Ok(v) => v,
+            #[allow(clippy::print_stderr)]
+            Err(e) => {
+                eprintln!("Error parsing -c overrides: {e}");
+                std::process::exit(1);
+            }
+        };
+
         #[allow(clippy::print_stderr)]
-        match Config::load_with_overrides(overrides) {
+        match Config::load_with_cli_overrides(cli_kv_overrides, overrides) {
             Ok(config) => config,
             Err(err) => {
                 eprintln!("Error loading configuration: {err}");

codex-rs/tui/src/main.rs

@@ -1,11 +1,26 @@
 use clap::Parser;
+use codex_common::CliConfigOverrides;
 use codex_tui::Cli;
 use codex_tui::run_main;
 
+#[derive(Parser, Debug)]
+struct TopCli {
+    #[clap(flatten)]
+    config_overrides: CliConfigOverrides,
+
+    #[clap(flatten)]
+    inner: Cli,
+}
+
 fn main() -> anyhow::Result<()> {
     codex_linux_sandbox::run_with_sandbox(|codex_linux_sandbox_exe| async move {
-        let cli = Cli::parse();
-        run_main(cli, codex_linux_sandbox_exe)?;
+        let top_cli = TopCli::parse();
+        let mut inner = top_cli.inner;
+        inner
+            .config_overrides
+            .raw_overrides
+            .splice(0..0, top_cli.config_overrides.raw_overrides);
+        run_main(inner, codex_linux_sandbox_exe)?;
         Ok(())
     })
 }