[codex] allow disabling prompt instruction blocks (#16735)

This PR adds root and profile config switches to omit the generated
`<permissions instructions>` and `<apps_instructions>` prompt blocks
while keeping both enabled by default, and it gates both the initial
developer-context injection and later permissions diff injection so
turning the permissions block off stays effective across turn-context
overrides.

Also added a prompt debug tool that can be used as `codex debug
prompt-input "hello"` and dumps the constructed items list.

codex-rs/core/src/config/config_tests.rs

@@ -4493,6 +4493,8 @@ fn test_precedence_fixture_with_o3_profile() -> std::io::Result<()> {
             base_instructions: None,
             developer_instructions: None,
             guardian_developer_instructions: None,
+            include_permissions_instructions: true,
+            include_apps_instructions: true,
             compact_prompt: None,
             commit_attribution: None,
             forced_chatgpt_workspace_id: None,
@@ -4635,6 +4637,8 @@ fn test_precedence_fixture_with_gpt3_profile() -> std::io::Result<()> {
         base_instructions: None,
         developer_instructions: None,
         guardian_developer_instructions: None,
+        include_permissions_instructions: true,
+        include_apps_instructions: true,
         compact_prompt: None,
         commit_attribution: None,
         forced_chatgpt_workspace_id: None,
@@ -4775,6 +4779,8 @@ fn test_precedence_fixture_with_zdr_profile() -> std::io::Result<()> {
         base_instructions: None,
         developer_instructions: None,
         guardian_developer_instructions: None,
+        include_permissions_instructions: true,
+        include_apps_instructions: true,
         compact_prompt: None,
         commit_attribution: None,
         forced_chatgpt_workspace_id: None,
@@ -4901,6 +4907,8 @@ fn test_precedence_fixture_with_gpt5_profile() -> std::io::Result<()> {
         base_instructions: None,
         developer_instructions: None,
         guardian_developer_instructions: None,
+        include_permissions_instructions: true,
+        include_apps_instructions: true,
         compact_prompt: None,
         commit_attribution: None,
         forced_chatgpt_workspace_id: None,
@@ -5783,6 +5791,32 @@ async fn approvals_reviewer_defaults_to_manual_only_without_guardian_feature() -
     Ok(())
 }
 
+#[tokio::test]
+async fn prompt_instruction_blocks_can_be_disabled_from_config_and_profiles() -> std::io::Result<()>
+{
+    let codex_home = TempDir::new()?;
+    std::fs::write(
+        codex_home.path().join(CONFIG_TOML_FILE),
+        r#"include_permissions_instructions = false
+include_apps_instructions = false
+profile = "chatty"
+
+[profiles.chatty]
+include_permissions_instructions = true
+"#,
+    )?;
+
+    let config = ConfigBuilder::default()
+        .codex_home(codex_home.path().to_path_buf())
+        .fallback_cwd(Some(codex_home.path().to_path_buf()))
+        .build()
+        .await?;
+
+    assert!(config.include_permissions_instructions);
+    assert!(!config.include_apps_instructions);
+    Ok(())
+}
+
 #[tokio::test]
 async fn approvals_reviewer_stays_manual_only_when_guardian_feature_is_enabled()
 -> std::io::Result<()> {

codex-rs/core/src/config/mod.rs

@@ -280,6 +280,12 @@ pub struct Config {
     /// Guardian-specific developer instructions override from requirements.toml.
     pub guardian_developer_instructions: Option<String>,
 
+    /// Whether to inject the `<permissions instructions>` developer block.
+    pub include_permissions_instructions: bool,
+
+    /// Whether to inject the `<apps_instructions>` developer block.
+    pub include_apps_instructions: bool,
+
     /// Compact prompt override.
     pub compact_prompt: Option<String>,
 
@@ -1183,6 +1189,12 @@ pub struct ConfigToml {
     #[serde(default)]
     pub developer_instructions: Option<String>,
 
+    /// Whether to inject the `<permissions instructions>` developer block.
+    pub include_permissions_instructions: Option<bool>,
+
+    /// Whether to inject the `<apps_instructions>` developer block.
+    pub include_apps_instructions: Option<bool>,
+
     /// Optional path to a file containing model instructions that will override
     /// the built-in instructions for the selected model. Users are STRONGLY
     /// DISCOURAGED from using this field, as deviating from the instructions
@@ -2452,6 +2464,14 @@ impl Config {
             Self::try_read_non_empty_file(model_instructions_path, "model instructions file")?;
         let base_instructions = base_instructions.or(file_base_instructions);
         let developer_instructions = developer_instructions.or(cfg.developer_instructions);
+        let include_permissions_instructions = config_profile
+            .include_permissions_instructions
+            .or(cfg.include_permissions_instructions)
+            .unwrap_or(true);
+        let include_apps_instructions = config_profile
+            .include_apps_instructions
+            .or(cfg.include_apps_instructions)
+            .unwrap_or(true);
         let guardian_developer_instructions = guardian_developer_instructions_from_requirements(
             config_layer_stack.requirements_toml(),
         );
@@ -2618,6 +2638,8 @@ impl Config {
             developer_instructions,
             compact_prompt,
             commit_attribution,
+            include_permissions_instructions,
+            include_apps_instructions,
             // The config.toml omits "_mode" because it's a config file. However, "_mode"
             // is important in code to differentiate the mode from the store implementation.
             cli_auth_credentials_store_mode: cfg.cli_auth_credentials_store.unwrap_or_default(),

codex-rs/core/src/config/profile.rs

@@ -49,6 +49,8 @@ pub struct ConfigProfile {
     pub experimental_instructions_file: Option<AbsolutePathBuf>,
     pub experimental_compact_prompt_file: Option<AbsolutePathBuf>,
     pub include_apply_patch_tool: Option<bool>,
+    pub include_permissions_instructions: Option<bool>,
+    pub include_apps_instructions: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub tools_view_image: Option<bool>,