feat[app-serve]: config management (#7241)

codex-rs/app-server/src/config_api.rs

@@ -0,0 +1,974 @@
+use crate::error_code::INTERNAL_ERROR_CODE;
+use crate::error_code::INVALID_REQUEST_ERROR_CODE;
+use anyhow::anyhow;
+use codex_app_server_protocol::ConfigBatchWriteParams;
+use codex_app_server_protocol::ConfigLayer;
+use codex_app_server_protocol::ConfigLayerMetadata;
+use codex_app_server_protocol::ConfigLayerName;
+use codex_app_server_protocol::ConfigReadParams;
+use codex_app_server_protocol::ConfigReadResponse;
+use codex_app_server_protocol::ConfigValueWriteParams;
+use codex_app_server_protocol::ConfigWriteErrorCode;
+use codex_app_server_protocol::ConfigWriteResponse;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_app_server_protocol::MergeStrategy;
+use codex_app_server_protocol::OverriddenMetadata;
+use codex_app_server_protocol::WriteStatus;
+use codex_core::config::ConfigToml;
+use codex_core::config_loader::LoadedConfigLayers;
+use codex_core::config_loader::LoaderOverrides;
+use codex_core::config_loader::load_config_layers_with_overrides;
+use codex_core::config_loader::merge_toml_values;
+use serde_json::Value as JsonValue;
+use serde_json::json;
+use sha2::Digest;
+use sha2::Sha256;
+use std::collections::HashMap;
+use std::path::Path;
+use std::path::PathBuf;
+use tempfile::NamedTempFile;
+use tokio::task;
+use toml::Value as TomlValue;
+
+const SESSION_FLAGS_SOURCE: &str = "--config";
+const MDM_SOURCE: &str = "com.openai.codex/config_toml_base64";
+const CONFIG_FILE_NAME: &str = "config.toml";
+
+#[derive(Clone)]
+pub(crate) struct ConfigApi {
+    codex_home: PathBuf,
+    cli_overrides: Vec<(String, TomlValue)>,
+    loader_overrides: LoaderOverrides,
+}
+
+impl ConfigApi {
+    pub(crate) fn new(codex_home: PathBuf, cli_overrides: Vec<(String, TomlValue)>) -> Self {
+        Self {
+            codex_home,
+            cli_overrides,
+            loader_overrides: LoaderOverrides::default(),
+        }
+    }
+
+    #[cfg(test)]
+    fn with_overrides(
+        codex_home: PathBuf,
+        cli_overrides: Vec<(String, TomlValue)>,
+        loader_overrides: LoaderOverrides,
+    ) -> Self {
+        Self {
+            codex_home,
+            cli_overrides,
+            loader_overrides,
+        }
+    }
+
+    pub(crate) async fn read(
+        &self,
+        params: ConfigReadParams,
+    ) -> Result<ConfigReadResponse, JSONRPCErrorError> {
+        let layers = self
+            .load_layers_state()
+            .await
+            .map_err(|err| internal_error("failed to read configuration layers", err))?;
+
+        let effective = layers.effective_config();
+        validate_config(&effective).map_err(|err| internal_error("invalid configuration", err))?;
+
+        let response = ConfigReadResponse {
+            config: to_json_value(&effective),
+            origins: layers.origins(),
+            layers: params.include_layers.then(|| layers.layers_high_to_low()),
+        };
+
+        Ok(response)
+    }
+
+    pub(crate) async fn write_value(
+        &self,
+        params: ConfigValueWriteParams,
+    ) -> Result<ConfigWriteResponse, JSONRPCErrorError> {
+        let edits = vec![(params.key_path, params.value, params.merge_strategy)];
+        self.apply_edits(params.file_path, params.expected_version, edits)
+            .await
+    }
+
+    pub(crate) async fn batch_write(
+        &self,
+        params: ConfigBatchWriteParams,
+    ) -> Result<ConfigWriteResponse, JSONRPCErrorError> {
+        let edits = params
+            .edits
+            .into_iter()
+            .map(|edit| (edit.key_path, edit.value, edit.merge_strategy))
+            .collect();
+
+        self.apply_edits(params.file_path, params.expected_version, edits)
+            .await
+    }
+
+    async fn apply_edits(
+        &self,
+        file_path: String,
+        expected_version: Option<String>,
+        edits: Vec<(String, JsonValue, MergeStrategy)>,
+    ) -> Result<ConfigWriteResponse, JSONRPCErrorError> {
+        let allowed_path = self.codex_home.join(CONFIG_FILE_NAME);
+        if !paths_match(&allowed_path, &file_path) {
+            return Err(config_write_error(
+                ConfigWriteErrorCode::ConfigLayerReadonly,
+                "Only writes to the user config are allowed",
+            ));
+        }
+
+        let layers = self
+            .load_layers_state()
+            .await
+            .map_err(|err| internal_error("failed to load configuration", err))?;
+
+        if let Some(expected) = expected_version.as_deref()
+            && expected != layers.user.version
+        {
+            return Err(config_write_error(
+                ConfigWriteErrorCode::ConfigVersionConflict,
+                "Configuration was modified since last read. Fetch latest version and retry.",
+            ));
+        }
+
+        let mut user_config = layers.user.config.clone();
+        let mut mutated = false;
+        let mut parsed_segments = Vec::new();
+
+        for (key_path, value, strategy) in edits.into_iter() {
+            let segments = parse_key_path(&key_path).map_err(|message| {
+                config_write_error(ConfigWriteErrorCode::ConfigValidationError, message)
+            })?;
+            let parsed_value = parse_value(value).map_err(|message| {
+                config_write_error(ConfigWriteErrorCode::ConfigValidationError, message)
+            })?;
+
+            let changed = apply_merge(&mut user_config, &segments, parsed_value.as_ref(), strategy)
+                .map_err(|err| match err {
+                    MergeError::PathNotFound => config_write_error(
+                        ConfigWriteErrorCode::ConfigPathNotFound,
+                        "Path not found",
+                    ),
+                    MergeError::Validation(message) => {
+                        config_write_error(ConfigWriteErrorCode::ConfigValidationError, message)
+                    }
+                })?;
+
+            mutated |= changed;
+            parsed_segments.push(segments);
+        }
+
+        validate_config(&user_config).map_err(|err| {
+            config_write_error(
+                ConfigWriteErrorCode::ConfigValidationError,
+                format!("Invalid configuration: {err}"),
+            )
+        })?;
+
+        let updated_layers = layers.with_user_config(user_config.clone());
+        let effective = updated_layers.effective_config();
+        validate_config(&effective).map_err(|err| {
+            config_write_error(
+                ConfigWriteErrorCode::ConfigValidationError,
+                format!("Invalid configuration: {err}"),
+            )
+        })?;
+
+        if mutated {
+            self.persist_user_config(&user_config)
+                .await
+                .map_err(|err| internal_error("failed to persist config.toml", err))?;
+        }
+
+        let overridden = first_overridden_edit(&updated_layers, &effective, &parsed_segments);
+        let status = overridden
+            .as_ref()
+            .map(|_| WriteStatus::OkOverridden)
+            .unwrap_or(WriteStatus::Ok);
+
+        Ok(ConfigWriteResponse {
+            status,
+            version: updated_layers.user.version.clone(),
+            overridden_metadata: overridden,
+        })
+    }
+
+    async fn load_layers_state(&self) -> std::io::Result<LayersState> {
+        let LoadedConfigLayers {
+            base,
+            managed_config,
+            managed_preferences,
+        } = load_config_layers_with_overrides(&self.codex_home, self.loader_overrides.clone())
+            .await?;
+
+        let user = LayerState::new(
+            ConfigLayerName::User,
+            self.codex_home.join(CONFIG_FILE_NAME),
+            base,
+        );
+
+        let session_flags = LayerState::new(
+            ConfigLayerName::SessionFlags,
+            PathBuf::from(SESSION_FLAGS_SOURCE),
+            {
+                let mut root = TomlValue::Table(toml::map::Map::new());
+                for (path, value) in self.cli_overrides.iter() {
+                    apply_override(&mut root, path, value.clone());
+                }
+                root
+            },
+        );
+
+        let system = managed_config.map(|cfg| {
+            LayerState::new(
+                ConfigLayerName::System,
+                system_config_path(&self.codex_home),
+                cfg,
+            )
+        });
+
+        let mdm = managed_preferences
+            .map(|cfg| LayerState::new(ConfigLayerName::Mdm, PathBuf::from(MDM_SOURCE), cfg));
+
+        Ok(LayersState {
+            user,
+            session_flags,
+            system,
+            mdm,
+        })
+    }
+
+    async fn persist_user_config(&self, user_config: &TomlValue) -> anyhow::Result<()> {
+        let codex_home = self.codex_home.clone();
+        let serialized = toml::to_string_pretty(user_config)?;
+
+        task::spawn_blocking(move || -> anyhow::Result<()> {
+            std::fs::create_dir_all(&codex_home)?;
+
+            let target = codex_home.join(CONFIG_FILE_NAME);
+            let tmp = NamedTempFile::new_in(&codex_home)?;
+            std::fs::write(tmp.path(), serialized.as_bytes())?;
+            tmp.persist(&target)?;
+            Ok(())
+        })
+        .await
+        .map_err(|err| anyhow!("config persistence task panicked: {err}"))??;
+
+        Ok(())
+    }
+}
+
+fn parse_value(value: JsonValue) -> Result<Option<TomlValue>, String> {
+    if value.is_null() {
+        return Ok(None);
+    }
+
+    serde_json::from_value::<TomlValue>(value)
+        .map(Some)
+        .map_err(|err| format!("invalid value: {err}"))
+}
+
+fn parse_key_path(path: &str) -> Result<Vec<String>, String> {
+    if path.trim().is_empty() {
+        return Err("keyPath must not be empty".to_string());
+    }
+    Ok(path
+        .split('.')
+        .map(std::string::ToString::to_string)
+        .collect())
+}
+
+fn apply_override(target: &mut TomlValue, path: &str, value: TomlValue) {
+    use toml::value::Table;
+
+    let segments: Vec<&str> = path.split('.').collect();
+    let mut current = target;
+
+    for (idx, segment) in segments.iter().enumerate() {
+        let is_last = idx == segments.len() - 1;
+
+        if is_last {
+            match current {
+                TomlValue::Table(table) => {
+                    table.insert(segment.to_string(), value);
+                }
+                _ => {
+                    let mut table = Table::new();
+                    table.insert(segment.to_string(), value);
+                    *current = TomlValue::Table(table);
+                }
+            }
+            return;
+        }
+
+        match current {
+            TomlValue::Table(table) => {
+                current = table
+                    .entry((*segment).to_string())
+                    .or_insert_with(|| TomlValue::Table(Table::new()));
+            }
+            _ => {
+                *current = TomlValue::Table(Table::new());
+                if let TomlValue::Table(tbl) = current {
+                    current = tbl
+                        .entry((*segment).to_string())
+                        .or_insert_with(|| TomlValue::Table(Table::new()));
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+enum MergeError {
+    PathNotFound,
+    Validation(String),
+}
+
+fn apply_merge(
+    root: &mut TomlValue,
+    segments: &[String],
+    value: Option<&TomlValue>,
+    strategy: MergeStrategy,
+) -> Result<bool, MergeError> {
+    let Some(value) = value else {
+        return clear_path(root, segments);
+    };
+
+    let Some((last, parents)) = segments.split_last() else {
+        return Err(MergeError::Validation(
+            "keyPath must not be empty".to_string(),
+        ));
+    };
+
+    let mut current = root;
+
+    for segment in parents {
+        match current {
+            TomlValue::Table(table) => {
+                current = table
+                    .entry(segment.clone())
+                    .or_insert_with(|| TomlValue::Table(toml::map::Map::new()));
+            }
+            _ => {
+                *current = TomlValue::Table(toml::map::Map::new());
+                if let TomlValue::Table(table) = current {
+                    current = table
+                        .entry(segment.clone())
+                        .or_insert_with(|| TomlValue::Table(toml::map::Map::new()));
+                }
+            }
+        }
+    }
+
+    let table = current.as_table_mut().ok_or_else(|| {
+        MergeError::Validation("cannot set value on non-table parent".to_string())
+    })?;
+
+    if matches!(strategy, MergeStrategy::Upsert)
+        && let Some(existing) = table.get_mut(last)
+        && matches!(existing, TomlValue::Table(_))
+        && matches!(value, TomlValue::Table(_))
+    {
+        merge_toml_values(existing, value);
+        return Ok(true);
+    }
+
+    let changed = table
+        .get(last)
+        .map(|existing| Some(existing) != Some(value))
+        .unwrap_or(true);
+    table.insert(last.clone(), value.clone());
+    Ok(changed)
+}
+
+fn clear_path(root: &mut TomlValue, segments: &[String]) -> Result<bool, MergeError> {
+    let Some((last, parents)) = segments.split_last() else {
+        return Err(MergeError::Validation(
+            "keyPath must not be empty".to_string(),
+        ));
+    };
+
+    let mut current = root;
+    for segment in parents {
+        match current {
+            TomlValue::Table(table) => {
+                current = table.get_mut(segment).ok_or(MergeError::PathNotFound)?;
+            }
+            _ => return Err(MergeError::PathNotFound),
+        }
+    }
+
+    let Some(parent) = current.as_table_mut() else {
+        return Err(MergeError::PathNotFound);
+    };
+
+    Ok(parent.remove(last).is_some())
+}
+
+#[derive(Clone)]
+struct LayerState {
+    name: ConfigLayerName,
+    source: PathBuf,
+    config: TomlValue,
+    version: String,
+}
+
+impl LayerState {
+    fn new(name: ConfigLayerName, source: PathBuf, config: TomlValue) -> Self {
+        let version = version_for_toml(&config);
+        Self {
+            name,
+            source,
+            config,
+            version,
+        }
+    }
+
+    fn metadata(&self) -> ConfigLayerMetadata {
+        ConfigLayerMetadata {
+            name: self.name.clone(),
+            source: self.source.display().to_string(),
+            version: self.version.clone(),
+        }
+    }
+
+    fn as_layer(&self) -> ConfigLayer {
+        ConfigLayer {
+            name: self.name.clone(),
+            source: self.source.display().to_string(),
+            version: self.version.clone(),
+            config: to_json_value(&self.config),
+        }
+    }
+}
+
+#[derive(Clone)]
+struct LayersState {
+    user: LayerState,
+    session_flags: LayerState,
+    system: Option<LayerState>,
+    mdm: Option<LayerState>,
+}
+
+impl LayersState {
+    fn with_user_config(self, user_config: TomlValue) -> Self {
+        Self {
+            user: LayerState::new(self.user.name, self.user.source, user_config),
+            session_flags: self.session_flags,
+            system: self.system,
+            mdm: self.mdm,
+        }
+    }
+
+    fn effective_config(&self) -> TomlValue {
+        let mut merged = self.user.config.clone();
+        merge_toml_values(&mut merged, &self.session_flags.config);
+        if let Some(system) = &self.system {
+            merge_toml_values(&mut merged, &system.config);
+        }
+        if let Some(mdm) = &self.mdm {
+            merge_toml_values(&mut merged, &mdm.config);
+        }
+        merged
+    }
+
+    fn origins(&self) -> HashMap<String, ConfigLayerMetadata> {
+        let mut origins = HashMap::new();
+        let mut path = Vec::new();
+
+        record_origins(
+            &self.user.config,
+            &self.user.metadata(),
+            &mut path,
+            &mut origins,
+        );
+        record_origins(
+            &self.session_flags.config,
+            &self.session_flags.metadata(),
+            &mut path,
+            &mut origins,
+        );
+        if let Some(system) = &self.system {
+            record_origins(&system.config, &system.metadata(), &mut path, &mut origins);
+        }
+        if let Some(mdm) = &self.mdm {
+            record_origins(&mdm.config, &mdm.metadata(), &mut path, &mut origins);
+        }
+
+        origins
+    }
+
+    fn layers_high_to_low(&self) -> Vec<ConfigLayer> {
+        let mut layers = Vec::new();
+        if let Some(mdm) = &self.mdm {
+            layers.push(mdm.as_layer());
+        }
+        if let Some(system) = &self.system {
+            layers.push(system.as_layer());
+        }
+        layers.push(self.session_flags.as_layer());
+        layers.push(self.user.as_layer());
+        layers
+    }
+}
+
+fn record_origins(
+    value: &TomlValue,
+    meta: &ConfigLayerMetadata,
+    path: &mut Vec<String>,
+    origins: &mut HashMap<String, ConfigLayerMetadata>,
+) {
+    match value {
+        TomlValue::Table(table) => {
+            for (key, val) in table {
+                path.push(key.clone());
+                record_origins(val, meta, path, origins);
+                path.pop();
+            }
+        }
+        TomlValue::Array(items) => {
+            for (idx, item) in items.iter().enumerate() {
+                path.push(idx.to_string());
+                record_origins(item, meta, path, origins);
+                path.pop();
+            }
+        }
+        _ => {
+            if !path.is_empty() {
+                origins.insert(path.join("."), meta.clone());
+            }
+        }
+    }
+}
+
+fn to_json_value(value: &TomlValue) -> JsonValue {
+    serde_json::to_value(value).unwrap_or(JsonValue::Null)
+}
+
+fn validate_config(value: &TomlValue) -> Result<(), toml::de::Error> {
+    let _: ConfigToml = value.clone().try_into()?;
+    Ok(())
+}
+
+fn version_for_toml(value: &TomlValue) -> String {
+    let json = to_json_value(value);
+    let canonical = canonical_json(&json);
+    let serialized = serde_json::to_vec(&canonical).unwrap_or_default();
+    let mut hasher = Sha256::new();
+    hasher.update(serialized);
+    let hash = hasher.finalize();
+    let hex = hash
+        .iter()
+        .map(|byte| format!("{byte:02x}"))
+        .collect::<String>();
+    format!("sha256:{hex}")
+}
+
+fn canonical_json(value: &JsonValue) -> JsonValue {
+    match value {
+        JsonValue::Object(map) => {
+            let mut sorted = serde_json::Map::new();
+            let mut keys = map.keys().cloned().collect::<Vec<_>>();
+            keys.sort();
+            for key in keys {
+                if let Some(val) = map.get(&key) {
+                    sorted.insert(key, canonical_json(val));
+                }
+            }
+            JsonValue::Object(sorted)
+        }
+        JsonValue::Array(items) => JsonValue::Array(items.iter().map(canonical_json).collect()),
+        other => other.clone(),
+    }
+}
+
+fn paths_match(expected: &Path, provided: &str) -> bool {
+    let provided_path = PathBuf::from(provided);
+    if let (Ok(expanded_expected), Ok(expanded_provided)) =
+        (expected.canonicalize(), provided_path.canonicalize())
+    {
+        return expanded_expected == expanded_provided;
+    }
+
+    expected == provided_path
+}
+
+fn value_at_path<'a>(root: &'a TomlValue, segments: &[String]) -> Option<&'a TomlValue> {
+    let mut current = root;
+    for segment in segments {
+        match current {
+            TomlValue::Table(table) => {
+                current = table.get(segment)?;
+            }
+            TomlValue::Array(items) => {
+                let idx: usize = segment.parse().ok()?;
+                current = items.get(idx)?;
+            }
+            _ => return None,
+        }
+    }
+    Some(current)
+}
+
+fn override_message(layer: &ConfigLayerName) -> String {
+    match layer {
+        ConfigLayerName::Mdm => "Overridden by managed policy (mdm)".to_string(),
+        ConfigLayerName::System => "Overridden by managed config (system)".to_string(),
+        ConfigLayerName::SessionFlags => "Overridden by session flags".to_string(),
+        ConfigLayerName::User => "Overridden by user config".to_string(),
+    }
+}
+
+fn compute_override_metadata(
+    layers: &LayersState,
+    effective: &TomlValue,
+    segments: &[String],
+) -> Option<OverriddenMetadata> {
+    let user_value = value_at_path(&layers.user.config, segments);
+    let effective_value = value_at_path(effective, segments);
+
+    if user_value.is_some() && user_value == effective_value {
+        return None;
+    }
+
+    if user_value.is_none() && effective_value.is_none() {
+        return None;
+    }
+
+    let effective_layer = find_effective_layer(layers, segments);
+    let overriding_layer = effective_layer.unwrap_or_else(|| layers.user.metadata());
+    let message = override_message(&overriding_layer.name);
+
+    Some(OverriddenMetadata {
+        message,
+        overriding_layer,
+        effective_value: effective_value
+            .map(to_json_value)
+            .unwrap_or(JsonValue::Null),
+    })
+}
+
+fn first_overridden_edit(
+    layers: &LayersState,
+    effective: &TomlValue,
+    edits: &[Vec<String>],
+) -> Option<OverriddenMetadata> {
+    for segments in edits {
+        if let Some(meta) = compute_override_metadata(layers, effective, segments) {
+            return Some(meta);
+        }
+    }
+    None
+}
+
+fn find_effective_layer(layers: &LayersState, segments: &[String]) -> Option<ConfigLayerMetadata> {
+    let check =
+        |state: &LayerState| value_at_path(&state.config, segments).map(|_| state.metadata());
+
+    if let Some(mdm) = &layers.mdm
+        && let Some(meta) = check(mdm)
+    {
+        return Some(meta);
+    }
+    if let Some(system) = &layers.system
+        && let Some(meta) = check(system)
+    {
+        return Some(meta);
+    }
+    if let Some(meta) = check(&layers.session_flags) {
+        return Some(meta);
+    }
+    check(&layers.user)
+}
+
+fn system_config_path(codex_home: &Path) -> PathBuf {
+    if let Ok(path) = std::env::var("CODEX_MANAGED_CONFIG_PATH") {
+        return PathBuf::from(path);
+    }
+
+    #[cfg(unix)]
+    {
+        let _ = codex_home;
+        PathBuf::from("/etc/codex/managed_config.toml")
+    }
+
+    #[cfg(not(unix))]
+    {
+        codex_home.join("managed_config.toml")
+    }
+}
+
+fn internal_error<E: std::fmt::Display>(context: &str, err: E) -> JSONRPCErrorError {
+    JSONRPCErrorError {
+        code: INTERNAL_ERROR_CODE,
+        message: format!("{context}: {err}"),
+        data: None,
+    }
+}
+
+fn config_write_error(code: ConfigWriteErrorCode, message: impl Into<String>) -> JSONRPCErrorError {
+    JSONRPCErrorError {
+        code: INVALID_REQUEST_ERROR_CODE,
+        message: message.into(),
+        data: Some(json!({
+            "config_write_error_code": code,
+        })),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+    use tempfile::tempdir;
+
+    #[tokio::test]
+    async fn read_includes_origins_and_layers() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(tmp.path().join(CONFIG_FILE_NAME), "model = \"user\"").unwrap();
+
+        let managed_path = tmp.path().join("managed_config.toml");
+        std::fs::write(&managed_path, "approval_policy = \"never\"").unwrap();
+
+        let api = ConfigApi::with_overrides(
+            tmp.path().to_path_buf(),
+            vec![],
+            LoaderOverrides {
+                managed_config_path: Some(managed_path),
+                #[cfg(target_os = "macos")]
+                managed_preferences_base64: None,
+            },
+        );
+
+        let response = api
+            .read(ConfigReadParams {
+                include_layers: true,
+            })
+            .await
+            .expect("response");
+
+        assert_eq!(
+            response.config.get("approval_policy"),
+            Some(&json!("never"))
+        );
+
+        assert_eq!(
+            response
+                .origins
+                .get("approval_policy")
+                .expect("origin")
+                .name,
+            ConfigLayerName::System
+        );
+        let layers = response.layers.expect("layers present");
+        assert_eq!(layers.first().unwrap().name, ConfigLayerName::System);
+        assert_eq!(layers.get(1).unwrap().name, ConfigLayerName::SessionFlags);
+        assert_eq!(layers.last().unwrap().name, ConfigLayerName::User);
+    }
+
+    #[tokio::test]
+    async fn write_value_reports_override() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(
+            tmp.path().join(CONFIG_FILE_NAME),
+            "approval_policy = \"on-request\"",
+        )
+        .unwrap();
+
+        let managed_path = tmp.path().join("managed_config.toml");
+        std::fs::write(&managed_path, "approval_policy = \"never\"").unwrap();
+
+        let api = ConfigApi::with_overrides(
+            tmp.path().to_path_buf(),
+            vec![],
+            LoaderOverrides {
+                managed_config_path: Some(managed_path),
+                #[cfg(target_os = "macos")]
+                managed_preferences_base64: None,
+            },
+        );
+
+        let result = api
+            .write_value(ConfigValueWriteParams {
+                file_path: tmp.path().join(CONFIG_FILE_NAME).display().to_string(),
+                key_path: "approval_policy".to_string(),
+                value: json!("never"),
+                merge_strategy: MergeStrategy::Replace,
+                expected_version: None,
+            })
+            .await
+            .expect("result");
+
+        let read_after = api
+            .read(ConfigReadParams {
+                include_layers: true,
+            })
+            .await
+            .expect("read");
+        let config_object = read_after.config.as_object().expect("object");
+        assert_eq!(config_object.get("approval_policy"), Some(&json!("never")));
+        assert_eq!(
+            read_after
+                .origins
+                .get("approval_policy")
+                .expect("origin")
+                .name,
+            ConfigLayerName::System
+        );
+        assert_eq!(result.status, WriteStatus::Ok);
+        assert!(result.overridden_metadata.is_none());
+    }
+
+    #[tokio::test]
+    async fn version_conflict_rejected() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(tmp.path().join(CONFIG_FILE_NAME), "model = \"user\"").unwrap();
+
+        let api = ConfigApi::new(tmp.path().to_path_buf(), vec![]);
+        let error = api
+            .write_value(ConfigValueWriteParams {
+                file_path: tmp.path().join(CONFIG_FILE_NAME).display().to_string(),
+                key_path: "model".to_string(),
+                value: json!("gpt-5"),
+                merge_strategy: MergeStrategy::Replace,
+                expected_version: Some("sha256:bogus".to_string()),
+            })
+            .await
+            .expect_err("should fail");
+
+        assert_eq!(error.code, INVALID_REQUEST_ERROR_CODE);
+        assert_eq!(
+            error
+                .data
+                .as_ref()
+                .and_then(|d| d.get("config_write_error_code"))
+                .and_then(serde_json::Value::as_str),
+            Some("configVersionConflict")
+        );
+    }
+
+    #[tokio::test]
+    async fn invalid_user_value_rejected_even_if_overridden_by_managed() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(tmp.path().join(CONFIG_FILE_NAME), "model = \"user\"").unwrap();
+
+        let managed_path = tmp.path().join("managed_config.toml");
+        std::fs::write(&managed_path, "approval_policy = \"never\"").unwrap();
+
+        let api = ConfigApi::with_overrides(
+            tmp.path().to_path_buf(),
+            vec![],
+            LoaderOverrides {
+                managed_config_path: Some(managed_path),
+                #[cfg(target_os = "macos")]
+                managed_preferences_base64: None,
+            },
+        );
+
+        let error = api
+            .write_value(ConfigValueWriteParams {
+                file_path: tmp.path().join(CONFIG_FILE_NAME).display().to_string(),
+                key_path: "approval_policy".to_string(),
+                value: json!("bogus"),
+                merge_strategy: MergeStrategy::Replace,
+                expected_version: None,
+            })
+            .await
+            .expect_err("should fail validation");
+
+        assert_eq!(error.code, INVALID_REQUEST_ERROR_CODE);
+        assert_eq!(
+            error
+                .data
+                .as_ref()
+                .and_then(|d| d.get("config_write_error_code"))
+                .and_then(serde_json::Value::as_str),
+            Some("configValidationError")
+        );
+
+        let contents =
+            std::fs::read_to_string(tmp.path().join(CONFIG_FILE_NAME)).expect("read config");
+        assert_eq!(contents.trim(), "model = \"user\"");
+    }
+
+    #[tokio::test]
+    async fn read_reports_managed_overrides_user_and_session_flags() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(tmp.path().join(CONFIG_FILE_NAME), "model = \"user\"").unwrap();
+
+        let managed_path = tmp.path().join("managed_config.toml");
+        std::fs::write(&managed_path, "model = \"system\"").unwrap();
+
+        let cli_overrides = vec![(
+            "model".to_string(),
+            TomlValue::String("session".to_string()),
+        )];
+
+        let api = ConfigApi::with_overrides(
+            tmp.path().to_path_buf(),
+            cli_overrides,
+            LoaderOverrides {
+                managed_config_path: Some(managed_path),
+                #[cfg(target_os = "macos")]
+                managed_preferences_base64: None,
+            },
+        );
+
+        let response = api
+            .read(ConfigReadParams {
+                include_layers: true,
+            })
+            .await
+            .expect("response");
+
+        assert_eq!(response.config.get("model"), Some(&json!("system")));
+        assert_eq!(
+            response.origins.get("model").expect("origin").name,
+            ConfigLayerName::System
+        );
+        let layers = response.layers.expect("layers");
+        assert_eq!(layers.first().unwrap().name, ConfigLayerName::System);
+        assert_eq!(layers.get(1).unwrap().name, ConfigLayerName::SessionFlags);
+        assert_eq!(layers.get(2).unwrap().name, ConfigLayerName::User);
+    }
+
+    #[tokio::test]
+    async fn write_value_reports_managed_override() {
+        let tmp = tempdir().expect("tempdir");
+        std::fs::write(tmp.path().join(CONFIG_FILE_NAME), "").unwrap();
+
+        let managed_path = tmp.path().join("managed_config.toml");
+        std::fs::write(&managed_path, "approval_policy = \"never\"").unwrap();
+
+        let api = ConfigApi::with_overrides(
+            tmp.path().to_path_buf(),
+            vec![],
+            LoaderOverrides {
+                managed_config_path: Some(managed_path),
+                #[cfg(target_os = "macos")]
+                managed_preferences_base64: None,
+            },
+        );
+
+        let result = api
+            .write_value(ConfigValueWriteParams {
+                file_path: tmp.path().join(CONFIG_FILE_NAME).display().to_string(),
+                key_path: "approval_policy".to_string(),
+                value: json!("on-request"),
+                merge_strategy: MergeStrategy::Replace,
+                expected_version: None,
+            })
+            .await
+            .expect("result");
+
+        assert_eq!(result.status, WriteStatus::OkOverridden);
+        let overridden = result.overridden_metadata.expect("overridden metadata");
+        assert_eq!(overridden.overriding_layer.name, ConfigLayerName::System);
+        assert_eq!(overridden.effective_value, json!("never"));
+    }
+}