[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/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(),