codex-skills-extension: pass ModelInfo context window in SkillsExtension::contribute_thread_context

The bug is in codex-rs/ext/skills/src/extension.rs, inside contribute_thread_context, where the budget call passes None for the context window even though ModelInfo is already read from thread_store. Start by reading how contribute_world_state derives its context window from model_info, then check the existing tests in codex-rs/ext/skills/tests/skills_extension.rs. Done when a custom provider's thread-context rendering respects resolved_context_window() and cargo test -p codex-skills-extension --test skills_extension passes.

Summary

In codex-rs/ext/skills/src/extension.rs, SkillsExtension::contribute_world_state scales the skill catalog token/character budget to the active model's context window via:

skill_metadata_budget(
    input.model_info.resolved_context_window(),
    config.max_context_tokens,
)

However, SkillsExtension::contribute_thread_context (codex-rs/ext/skills/src/extension.rs:234) hardcodes /*context_window*/ None:

skill_metadata_budget(/*context_window*/ None, config.max_context_tokens)

even though thread_store.get::<ModelInfo>() is already accessed on line 222 of the same method. Consequently, custom skill providers rendered on the CatalogSurface::ThreadContext surface always use DEFAULT_SKILL_METADATA_BUDGET instead of scaling to the thread model's resolved_context_window().

Expected Behavior

SkillsExtension::contribute_thread_context should extract model_info.as_deref().and_then(ModelInfo::resolved_context_window) from thread_store.get::<ModelInfo>() and pass it to skill_metadata_budget(context_window, config.max_context_tokens).

Environment

• Codex CLI version: 0.162.1 (aarch64-apple-darwin)
• Codex Desktop version: 26.1007.71326 (embedded CLI 0.162.0-alpha.17.2)
• OS: macOS aarch64

Root-Cause Analysis & Verification

Summary

• Reads model_info once from thread_store.get::<ModelInfo>() in SkillsExtension::contribute_thread_context (codex-rs/ext/skills/src/extension.rs).
• Passes model_info.as_deref().and_then(ModelInfo::resolved_context_window) to skill_metadata_budget(context_window, config.max_context_tokens) so CatalogSurface::ThreadContext respects the model's context window just like contribute_world_state.
• Adds behavioral test contribute_thread_context_uses_model_context_window_for_custom_provider_budget in codex-rs/ext/skills/tests/skills_extension.rs.

Verification

• cargo test --offline -p codex-skills-extension --test skills_extension (21 passed)

Reference Patch & Regression Tests (0002-fix-skills-pass-model-context-window-in-contribute-thread-context.patch)

From 852b78b2801e7000c4392bbf01839584b8e90d28 Mon Sep 17 00:00:00 2001
From: trukhinyuri <[email protected]>
Date: Thu, 15 Oct 2026 01:05:51 +0200
Subject: [PATCH] fix(skills): pass model context window in
 contribute_thread_context

---
 codex-rs/ext/skills/src/extension.rs          | 10 ++-
 codex-rs/ext/skills/tests/skills_extension.rs | 71 +++++++++++++++++++
 2 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/codex-rs/ext/skills/src/extension.rs b/codex-rs/ext/skills/src/extension.rs
index e2400b9..85cbb20 100644
--- a/codex-rs/ext/skills/src/extension.rs
+++ b/codex-rs/ext/skills/src/extension.rs
@@ -219,9 +219,13 @@ where
             for warning in bounded_warnings(&catalog.warnings) {
                 self.emit_warning(thread_store.level_id(), /*turn_id*/ None, warning);
             }
-            let include_usage = thread_store
-                .get::<ModelInfo>()
+            let model_info = thread_store.get::<ModelInfo>();
+            let include_usage = model_info
+                .as_deref()
                 .is_some_and(|model_info| model_info.include_skills_usage_instructions);
+            let context_window = model_info
+                .as_deref()
+                .and_then(ModelInfo::resolved_context_window);
             let extension_metrics = session_store
                 .get::<SkillsSessionState>()
                 .and_then(|state| state.extension_metrics.clone());
@@ -231,7 +235,7 @@ where
                 &catalog,
                 include_usage,
                 SkillCatalogRenderPolicy::ExtensionCompatible,
-                skill_metadata_budget(/*context_window*/ None, config.max_context_tokens),
+                skill_metadata_budget(context_window, config.max_context_tokens),
             );
             if let Some(message) = rendered.warning_message {
                 self.emit_warning(thread_store.level_id(), /*turn_id*/ None, message);
diff --git a/codex-rs/ext/skills/tests/skills_extension.rs b/codex-rs/ext/skills/tests/skills_extension.rs
index b0ee66b..1a16801 100644
--- a/codex-rs/ext/skills/tests/skills_extension.rs
+++ b/codex-rs/ext/skills/tests/skills_extension.rs
@@ -57,6 +57,7 @@ use codex_skills_extension::HostSkillsService;
 use codex_skills_extension::HostSkillsSnapshot;
 use codex_skills_extension::InjectedHostSkillPrompts;
 use codex_skills_extension::SkillLoadOutcome;
+use codex_skills_extension::SkillProviderSource;
 use codex_skills_extension::SkillProviders;
 use codex_skills_extension::SkillsExtensionConfig;
 use codex_skills_extension::catalog::SkillAuthority;
@@ -2687,3 +2688,73 @@ fn read_request_keys(
         .unwrap_or_else(std::sync::PoisonError::into_inner)
         .clone()
 }
+
+#[tokio::test]
+async fn contribute_thread_context_uses_model_context_window_for_custom_provider_budget()
+-> TestResult {
+    let custom_entries = (0..200)
+        .map(|index| {
+            test_entry(
+                SkillSourceKind::Custom("custom".to_string()),
+                "custom-authority",
+                &format!("custom/skill-{index:02}"),
+                &format!("skill-{index:02}/SKILL.md"),
+            )
+        })
+        .collect();
+    let providers = SkillProviders::new().with_provider(SkillProviderSource::new(
+        SkillSourceKind::Custom("custom".to_string()),
+        "custom",
+        Arc::new(StaticSkillProvider {
+            catalog: SkillCatalog {
+                entries: custom_entries,
+                warnings: Vec::new(),
+            },
+            read_requests: Arc::new(Mutex::new(Vec::new())),
+            list_calls: None,
+            fail_first_list: false,
+        }),
+    ));
+    let (event_tx, event_rx) = std::sync::mpsc::channel();
+    let mut builder =
+        ExtensionRegistryBuilder::with_event_sink(Arc::new(ChannelEventSink(event_tx)));
+    install_with_providers(&mut builder, providers, skills_extension_config);
+    let registry = builder.build();
+    let session_store = ExtensionData::new("session");
+    let thread_store = ExtensionData::new("thread");
+    let mut config = default_config();
+    config.bundled_skills_enabled = false;
+    registry.thread_lifecycle_contributors()[0]
+        .on_thread_start(ThreadStartInput {
+            config: &config,
+            session_source: &SessionSource::Cli,
+            persistent_thread_state_available: true,
+            environments: &[],
+            mcp_resource_client: None,
+            extension_metrics: None,
+            session_store: &session_store,
+            thread_store: &thread_store,
+        })
+        .await;
+    let mut model_info = model_info_from_slug("test-model");
+    model_info.context_window = Some(10_000);
+    thread_store.insert(model_info);
+
+    let thread_fragments = registry.context_contributors()[0]
+        .contribute_thread_context(&session_store, &thread_store)
+        .await;
+    assert_eq!(thread_fragments.len(), 1);
+    let rendered = thread_fragments[0].text();
+    assert!(!rendered.contains("skill-39"));
+    assert!(rendered.contains("additional skills omitted"));
+
+    let warning = event_rx.try_recv()?.into_warning();
+    assert_eq!(warning.thread_id, thread_store.level_id());
+    assert_eq!(warning.turn_id, None);
+    assert!(
+        warning
+            .message
+            .starts_with("Exceeded skills context budget.")
+    );
+    Ok(())
+}
-- 
2.56.0