Remove skill model delegation support (#39068)

## What changed

- Stop parsing and exposing the `model` field from skill frontmatter.
- Remove the skill model delegation types and instruction generation.

GitOrigin-RevId: 01198c68c095da5062e8abec417cc3539099d9d5

codex-rs/core-plugins/src/test_support.rs

@@ -187,7 +187,6 @@ fn load_test_skill_root(root: &PluginSkillRoot) -> LoadedSkillRoot {
                         name: format!("{}:{}", root.plugin_namespace, parsed.name),
                         description: parsed.description,
                         short_description: parsed.short_description,
-                        model: parsed.model,
                         interface: None,
                         dependencies: None,
                         policy: None,

codex-rs/ext/skills/src/dynamic_skill_selector/character_routing_card_tests.rs

@@ -24,7 +24,6 @@ fn host_interface_metadata_makes_unlisted_workflow_discoverable() {
         name: "content-tools".to_string(),
         description: "Prepare visual content.".to_string(),
         short_description: None,
-        model: None,
         interface: Some(SkillInterface {
             display_name: Some("Visual Assets".to_string()),
             short_description: Some("Create illustrated assets.".to_string()),

codex-rs/ext/skills/src/host_roots_tests.rs

@@ -225,7 +225,6 @@ fn expected_skill(path: AbsolutePathBuf, name: &str, scope: SkillScope) -> Skill
         name: name.to_string(),
         description: format!("{name} description"),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,

codex-rs/ext/skills/src/host_service_tests.rs

@@ -324,7 +324,6 @@ async fn snapshot_for_config_preserves_host_precedence_for_symlinked_plugin_root
             name: "sample:search".to_string(),
             description: "shared skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,

codex-rs/ext/skills/src/loader/environment.rs

@@ -72,7 +72,6 @@ impl ParsedEnvironmentSkill {
             name: base_name,
             description,
             short_description,
-            model: _,
         } = parse_skill_frontmatter_metadata(&contents, || default_skill_name(&skill.path))
             .map_err(|err| err.to_string())?;
         let (dependencies, policy) = match &skill.metadata {
@@ -241,7 +240,6 @@ pub fn load_environment_skills_from_discovery(
             name: base_name,
             description,
             short_description,
-            model: _,
         } = match parse_skill_frontmatter_metadata(&skill.instructions.contents, || {
             default_skill_name(&skill.instructions.path)
         }) {

codex-rs/ext/skills/src/loader/host.rs

@@ -356,7 +356,6 @@ async fn parse_skill_file(
         name,
         description,
         short_description,
-        model,
     } = parse_skill_frontmatter_metadata(&contents, || default_skill_name(path))
         .map_err(|error| error.to_string())?;
     let LoadedSkillMetadata {
@@ -369,7 +368,6 @@ async fn parse_skill_file(
         name,
         description,
         short_description,
-        model,
         interface,
         dependencies,
         policy,

codex-rs/ext/skills/src/loader/host_io_tests.rs

@@ -84,7 +84,6 @@ async fn host_loading_reuses_walk_inventory_for_symlinked_skill_pack() {
                 name: "linked:first".to_string(),
                 description: "first skill.".to_string(),
                 short_description: None,
-                model: None,
                 interface: None,
                 dependencies: None,
                 policy: Some(SkillPolicy {
@@ -100,7 +99,6 @@ async fn host_loading_reuses_walk_inventory_for_symlinked_skill_pack() {
                 name: "linked:second".to_string(),
                 description: "second skill.".to_string(),
                 short_description: None,
-                model: None,
                 interface: None,
                 dependencies: None,
                 policy: None,

codex-rs/ext/skills/src/loader/host_tests.rs

@@ -7,7 +7,6 @@ use codex_protocol::protocol::SkillScope;
 use codex_skills::SkillDependencies;
 use codex_skills::SkillInterface;
 use codex_skills::SkillMetadata;
-use codex_skills::SkillModel;
 use codex_skills::SkillPolicy;
 use codex_skills::SkillToolDependency;
 use codex_utils_absolute_path::AbsolutePathBuf;
@@ -108,7 +107,7 @@ async fn loads_host_frontmatter_dependencies_and_policy() {
     let skill_path = write_skill(
         &root,
         "demo",
-        "name: demo\ndescription: Demo skill\nmodel: luna\nmetadata:\n  short-description: Short demo",
+        "name: demo\ndescription: Demo skill\nmetadata:\n  short-description: Short demo",
     );
     write_metadata(
         &root,
@@ -135,7 +134,6 @@ policy:
             name: "demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: Some("Short demo".to_string()),
-            model: Some(SkillModel::Luna),
             interface: None,
             dependencies: Some(SkillDependencies {
                 tools: vec![SkillToolDependency {
@@ -175,7 +173,6 @@ async fn invalid_optional_metadata_fails_open() {
             name: "demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,
@@ -215,7 +212,6 @@ async fn loads_host_interface_metadata_and_local_asset_paths() {
             name: "demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
             interface: Some(SkillInterface {
                 display_name: Some("Demo".to_string()),
                 short_description: Some("Interface summary".to_string()),
@@ -255,7 +251,6 @@ async fn loads_plugin_skill_interface_icons_from_local_and_shared_assets() {
             name: "plugin:send-message".to_string(),
             description: "Send messages".to_string(),
             short_description: None,
-            model: None,
             interface: Some(SkillInterface {
                 display_name: None,
                 short_description: None,
@@ -298,7 +293,6 @@ async fn rejects_plugin_skill_interface_icons_outside_shared_assets() {
             name: "plugin:send-message".to_string(),
             description: "Send messages".to_string(),
             short_description: None,
-            model: None,
             interface: Some(SkillInterface {
                 display_name: Some("Send Message".to_string()),
                 short_description: None,
@@ -336,7 +330,6 @@ async fn rejects_interface_fields_that_escape_or_fail_validation() {
             name: "demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,
@@ -387,7 +380,6 @@ async fn discovers_nested_plugin_namespace_without_plugin_identity() {
             name: "plugin-name:demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,
@@ -433,7 +425,6 @@ async fn plugin_root_accepts_maximum_length_qualified_skill_name() {
             name: format!("{plugin_namespace}:{skill_name}"),
             description: "Search skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,
@@ -528,7 +519,6 @@ async fn recursive_plugin_root_preserves_owner_namespace_and_shared_asset_policy
             name: "plugin:demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
             interface: Some(SkillInterface {
                 display_name: None,
                 short_description: None,
@@ -588,7 +578,6 @@ async fn direct_child_plugin_root_ignores_nested_skills() {
             name: "plugin:direct".to_string(),
             description: "Direct skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,
@@ -670,7 +659,6 @@ async fn recursive_plugin_root_preserves_symlinked_skill_discovery_path() {
             name: "plugin:demo".to_string(),
             description: "Symlinked skill".to_string(),
             short_description: None,
-            model: None,
             interface: None,
             dependencies: None,
             policy: None,

codex-rs/ext/skills/tests/skills_extension.rs

@@ -175,7 +175,6 @@ async fn installed_extension_uses_host_service_snapshot() -> TestResult {
         name: "demo".to_string(),
         description: "Demo skill.".to_string(),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,
@@ -257,7 +256,6 @@ async fn host_world_state_records_catalog_metrics_on_publish_and_change() -> Tes
         name: "demo".to_string(),
         description: "Demo skill.".to_string(),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,
@@ -322,7 +320,6 @@ async fn host_world_state_records_catalog_metrics_on_publish_and_change() -> Tes
         name: "other".to_string(),
         description: "Other skill.".to_string(),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,
@@ -375,7 +372,6 @@ async fn persisted_host_snapshot_deduplicates_warning_after_reinitialization() -
         name: "demo".to_string(),
         description: "Demo skill.".to_string(),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,

codex-rs/skills/src/invocation_tests.rs

@@ -28,7 +28,6 @@ fn test_skill_metadata(skill_doc_path: AbsolutePathBuf) -> SkillMetadata {
         name: "test-skill".to_string(),
         description: "test".to_string(),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,

codex-rs/skills/src/lib.rs

@@ -3,7 +3,6 @@ mod invocation;
 mod loading;
 mod mentions;
 mod model;
-mod model_delegation;
 mod name_counts;
 mod parser;
 mod selection;
@@ -37,8 +36,6 @@ pub use model::SkillInterface;
 pub use model::SkillMetadata;
 pub use model::SkillPolicy;
 pub use model::SkillToolDependency;
-pub use model_delegation::SkillModel;
-pub use model_delegation::SkillModelDelegationInstruction;
 pub use name_counts::build_skill_name_counts;
 pub use parser::ParsedSkillFrontmatter;
 pub use parser::SkillParseError;

codex-rs/skills/src/model.rs

@@ -1,4 +1,3 @@
-use crate::SkillModel;
 use codex_protocol::protocol::Product;
 use codex_protocol::protocol::SkillScope;
 use codex_utils_absolute_path::AbsolutePathBuf;
@@ -10,8 +9,6 @@ pub struct SkillMetadata {
     pub name: String,
     pub description: String,
     pub short_description: Option<String>,
-    /// Optional model requested by this skill's frontmatter.
-    pub model: Option<SkillModel>,
     pub interface: Option<SkillInterface>,
     pub dependencies: Option<SkillDependencies>,
     pub policy: Option<SkillPolicy>,

codex-rs/skills/src/model_delegation.rs

@@ -1,84 +0,0 @@
-use serde::Deserialize;
-
-const LUNA_MODEL: &str = "gpt-5.6-luna";
-const TERRA_MODEL: &str = "gpt-5.6-terra";
-const SOL_MODEL: &str = "gpt-5.6-sol";
-const MAX_TARGET_MODEL_BYTES: usize = 128;
-const MAX_DELEGATION_INSTRUCTION_BYTES: usize = 2_048;
-
-/// Model requested for work governed by a skill.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Deserialize)]
-#[serde(rename_all = "lowercase")]
-pub enum SkillModel {
-    Luna,
-}
-
-/// Bounded instructions for delegating skill-governed work to a cheaper model.
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub struct SkillModelDelegationInstruction(String);
-
-impl SkillModelDelegationInstruction {
-    /// Builds bounded instructions only when the indexed skill requests an available lower-tier model.
-    pub fn from_skill_model(
-        skill_model: SkillModel,
-        skill_name: &str,
-        current_model: &str,
-        available_models: &[String],
-    ) -> Option<Self> {
-        if skill_name
-            .chars()
-            .any(|character| matches!(character, '`' | '<' | '>'))
-        {
-            return None;
-        }
-
-        let provider_prefix = [SOL_MODEL, TERRA_MODEL]
-            .into_iter()
-            .find_map(|parent_model| {
-                current_model.strip_suffix(parent_model).filter(|prefix| {
-                    prefix.is_empty() || prefix.ends_with('.') || prefix.ends_with('/')
-                })
-            })?;
-        let target_model = format!("{provider_prefix}{LUNA_MODEL}");
-        let target_model = available_models
-            .iter()
-            .find(|model| model.as_str() == target_model && is_safe_model_identifier(model))?;
-        let skill_model = match skill_model {
-            SkillModel::Luna => "luna",
-        };
-        let instruction = format!(
-            "<skill_model_delegation>\n\
-For this invocation only, skill `{skill_name}` requests `model: {skill_model}`. \
-If the user prohibits delegation or subagents, or the work depends on an image or audio \
-attachment, work locally. Otherwise, delegate only self-contained text-based skill work \
-and use `spawn_agent` \
-exactly once. Set `model` to `{target_model}`, set `fork_turns` to `\"none\"`, and choose a \
-unique `task_name`. Omit `agent_type` and `reasoning_effort`.\n\
-Give the child only this skill's work and necessary context; never include this block and tell \
-it not to spawn agents. Delegate the whole request only if the skill fully covers it; otherwise, \
-retain ownership of the remaining work and final answer. Wait for the result. If spawning \
-fails, continue locally. If waiting fails, retry waiting without duplicating the \
-child's work.\n\
-Ignore this instruction in child agents and on later turns.\n\
-</skill_model_delegation>"
-        );
-
-        (instruction.len() <= MAX_DELEGATION_INSTRUCTION_BYTES).then_some(Self(instruction))
-    }
-
-    /// Returns the bounded model-visible delegation instructions.
-    pub fn as_str(&self) -> &str {
-        &self.0
-    }
-}
-
-fn is_safe_model_identifier(model: &str) -> bool {
-    model.len() <= MAX_TARGET_MODEL_BYTES
-        && model.chars().all(|character| {
-            character.is_ascii_alphanumeric() || matches!(character, '.' | '/' | '_' | '-')
-        })
-}
-
-#[cfg(test)]
-#[path = "model_delegation_tests.rs"]
-mod tests;

codex-rs/skills/src/model_delegation_tests.rs

@@ -1,224 +0,0 @@
-use pretty_assertions::assert_eq;
-
-use super::MAX_DELEGATION_INSTRUCTION_BYTES;
-use super::SkillModel;
-use super::SkillModelDelegationInstruction;
-use crate::ParsedSkillFrontmatter;
-use crate::parse_skill_frontmatter_metadata;
-
-#[test]
-fn parses_supported_luna_skill_model() {
-    let contents = "---\nname: demo\ndescription: Demo skill\nmodel: luna\n---\n";
-
-    assert_eq!(
-        parse_skill_frontmatter_metadata(contents, || "fallback".to_string())
-            .unwrap()
-            .model,
-        Some(SkillModel::Luna)
-    );
-}
-
-#[test]
-fn permits_skills_without_a_model_annotation() {
-    let contents = "---\nname: demo\ndescription: Demo skill\n---\n";
-
-    assert_eq!(
-        parse_skill_frontmatter_metadata(contents, || "fallback".to_string())
-            .unwrap()
-            .model,
-        None
-    );
-}
-
-#[test]
-fn rejects_unsupported_model_without_disabling_ordinary_skill_loading() {
-    for unsupported_model in ["terra", "sol", "unknown"] {
-        let contents =
-            format!("---\nname: demo\ndescription: Demo skill\nmodel: {unsupported_model}\n---\n");
-
-        assert_eq!(
-            parse_skill_frontmatter_metadata(&contents, || "fallback".to_string()).unwrap(),
-            ParsedSkillFrontmatter {
-                name: "demo".to_string(),
-                description: "Demo skill".to_string(),
-                short_description: None,
-                model: None,
-            }
-        );
-    }
-}
-
-#[test]
-fn reuses_existing_frontmatter_scalar_repair() {
-    let contents = "---\nname: demo\ndescription: Build for AWS: ECS\nmodel: luna\n---\n";
-
-    assert_eq!(
-        parse_skill_frontmatter_metadata(contents, || "fallback".to_string())
-            .unwrap()
-            .model,
-        Some(SkillModel::Luna)
-    );
-}
-
-#[test]
-fn delegates_only_from_supported_parent_models() {
-    let available_models = available_models();
-    for (current_model, should_delegate) in [
-        ("gpt-5.6-sol", true),
-        ("gpt-5.6-terra", true),
-        ("gpt-5.6-luna", false),
-        ("gpt-5.5-codex", false),
-    ] {
-        let instruction = SkillModelDelegationInstruction::from_skill_model(
-            SkillModel::Luna,
-            "demo",
-            current_model,
-            &available_models,
-        );
-        assert_eq!(
-            instruction.is_some(),
-            should_delegate,
-            "current={current_model}"
-        );
-    }
-}
-
-#[test]
-fn resolves_luna_within_the_current_provider_namespace() {
-    for (current_model, target_model, unrelated_model) in [
-        ("gpt-5.6-sol", "gpt-5.6-luna", "openai.gpt-5.6-luna"),
-        (
-            "tenant-a/gpt-5.6-sol",
-            "tenant-a/gpt-5.6-luna",
-            "tenant-b/gpt-5.6-luna",
-        ),
-        (
-            "openai.gpt-5.6-terra",
-            "openai.gpt-5.6-luna",
-            "other.gpt-5.6-luna",
-        ),
-    ] {
-        let instruction = SkillModelDelegationInstruction::from_skill_model(
-            SkillModel::Luna,
-            "demo",
-            current_model,
-            &[unrelated_model.to_string(), target_model.to_string()],
-        )
-        .expect("lower-tier model in the same provider namespace should be resolved");
-
-        assert!(
-            instruction
-                .as_str()
-                .contains(&format!("Set `model` to `{target_model}`"))
-        );
-    }
-}
-
-#[test]
-fn rejects_targets_outside_the_current_provider_namespace() {
-    for (current_model, available_models) in [
-        (
-            "tenant-a/gpt-5.6-sol",
-            vec![
-                "tenant-b/gpt-5.6-luna".to_string(),
-                "gpt-5.6-luna".to_string(),
-            ],
-        ),
-        ("gpt-5.6-sol", vec!["tenant-a/gpt-5.6-luna".to_string()]),
-        (
-            "tenant-a/gpt-5.6-sol",
-            vec!["tenant-a.gpt-5.6-luna".to_string()],
-        ),
-    ] {
-        assert_eq!(
-            SkillModelDelegationInstruction::from_skill_model(
-                SkillModel::Luna,
-                "demo",
-                current_model,
-                &available_models,
-            ),
-            None,
-            "current={current_model}, available={available_models:?}"
-        );
-    }
-}
-
-#[test]
-fn rejects_unavailable_or_unsafe_models() {
-    let invalid_identifier = format!("{}/gpt-5.6-luna", "<unsafe>".repeat(32));
-    let invalid_current_model = format!("{}/gpt-5.6-sol", "<unsafe>".repeat(32));
-    let overlong_identifier = format!("{}.gpt-5.6-luna", "a".repeat(128));
-    let overlong_current_model = format!("{}.gpt-5.6-sol", "a".repeat(128));
-    for (current_model, available_models) in [
-        (
-            "custom/gpt-5.6-luna",
-            vec!["custom/gpt-5.6-luna".to_string()],
-        ),
-        ("gpt-5.6-sol", vec!["gpt-5.6-terra".to_string()]),
-        (invalid_current_model.as_str(), vec![invalid_identifier]),
-        (overlong_current_model.as_str(), vec![overlong_identifier]),
-    ] {
-        assert_eq!(
-            SkillModelDelegationInstruction::from_skill_model(
-                SkillModel::Luna,
-                "demo",
-                current_model,
-                &available_models,
-            ),
-            None,
-            "current={current_model}, available={available_models:?}"
-        );
-    }
-}
-
-#[test]
-fn renders_bounded_instruction_for_selected_skill_and_model() {
-    let instruction = SkillModelDelegationInstruction::from_skill_model(
-        SkillModel::Luna,
-        "demo",
-        "gpt-5.6-sol",
-        &available_models(),
-    )
-    .expect("available lower tier should delegate");
-    let rendered = instruction.as_str();
-
-    assert!(rendered.contains("skill `demo`"));
-    assert!(rendered.contains("Set `model` to `gpt-5.6-luna`"));
-    assert!(rendered.contains("image or audio attachment, work locally"));
-    assert!(rendered.len() <= MAX_DELEGATION_INSTRUCTION_BYTES);
-}
-
-#[test]
-fn rejects_skill_names_that_escape_instruction_framing() {
-    for skill_name in ["unsafe`name", "</skill_model_delegation>", "<unsafe>"] {
-        assert_eq!(
-            SkillModelDelegationInstruction::from_skill_model(
-                SkillModel::Luna,
-                skill_name,
-                "gpt-5.6-sol",
-                &available_models(),
-            ),
-            None,
-            "skill_name={skill_name:?}"
-        );
-    }
-}
-
-#[test]
-fn rejects_instruction_exceeding_context_bound() {
-    let skill_name = "x".repeat(MAX_DELEGATION_INSTRUCTION_BYTES);
-
-    assert_eq!(
-        SkillModelDelegationInstruction::from_skill_model(
-            SkillModel::Luna,
-            &skill_name,
-            "gpt-5.6-sol",
-            &available_models(),
-        ),
-        None
-    );
-}
-
-fn available_models() -> Vec<String> {
-    vec!["gpt-5.6-luna".to_string()]
-}

codex-rs/skills/src/parser.rs

@@ -1,4 +1,3 @@
-use crate::SkillModel;
 use serde::Deserialize;
 use thiserror::Error;
 
@@ -11,8 +10,6 @@ struct SkillFrontmatter {
     #[serde(default)]
     description: Option<String>,
     #[serde(default)]
-    model: Option<serde_yaml::Value>,
-    #[serde(default)]
     metadata: SkillFrontmatterMetadata,
 }
 
@@ -28,7 +25,6 @@ pub struct ParsedSkillFrontmatter {
     pub name: String,
     pub description: String,
     pub short_description: Option<String>,
-    pub model: Option<SkillModel>,
 }
 
 /// Error produced while parsing or validating `SKILL.md` metadata.
@@ -92,13 +88,6 @@ pub fn parse_skill_frontmatter_metadata(
         name,
         description,
         short_description,
-        model: parsed.model.and_then(|model| {
-            serde_yaml::from_value(model)
-                .inspect_err(|error| {
-                    tracing::warn!(%error, "ignoring invalid skill model annotation");
-                })
-                .ok()
-        }),
     })
 }
 

codex-rs/skills/src/parser_tests.rs

@@ -17,7 +17,6 @@ fn parses_repairs_and_sanitizes_frontmatter() {
             name: "deploy service".to_string(),
             description: "Build for AWS: ECS".to_string(),
             short_description: Some("Deploy safely".to_string()),
-            model: None,
         }
     );
 }
@@ -34,7 +33,6 @@ fn uses_default_name_and_requires_description() {
             name: "demo".to_string(),
             description: "Demo skill".to_string(),
             short_description: None,
-            model: None,
         }
     );
 
@@ -58,7 +56,6 @@ fn repairs_short_descriptions_containing_colons_and_apostrophes() {
             name: "short".to_string(),
             description: "Short skill".to_string(),
             short_description: Some("What's included: builds and tests".to_string()),
-            model: None,
         }
     );
 }
@@ -77,7 +74,6 @@ fn repairs_unrecognized_frontmatter_fields_that_need_quotes() {
             name: "unknown".to_string(),
             description: "Unknown fields".to_string(),
             short_description: None,
-            model: None,
         }
     );
 }
@@ -96,7 +92,6 @@ fn preserves_block_scalar_bodies_while_repairing_other_fields() {
             name: "block".to_string(),
             description: "Build for AWS: ECS".to_string(),
             short_description: None,
-            model: None,
         }
     );
 }
@@ -119,7 +114,6 @@ fn preserves_overlong_descriptions_and_short_descriptions() {
             name: "long".to_string(),
             description,
             short_description: Some(short_description),
-            model: None,
         }
     );
 }

codex-rs/skills/src/selection_tests.rs

@@ -32,7 +32,6 @@ fn make_skill(name: &str, path: &str) -> SkillMetadata {
         name: name.to_string(),
         description: format!("{name} skill"),
         short_description: None,
-        model: None,
         interface: None,
         dependencies: None,
         policy: None,