skills: cache remote catalog failures per thread

[jif-oai]

Summary

• cache the first remote skill catalog outcome per thread, including failures
• preserve discovery errors as catalog warnings
• update the existing cache regression test to verify failed discovery is attempted once

Why

A failed or hanging codex_apps resources/list call could run once while building initial context and immediately again while contributing first-turn input. With the discovery timeout, an ordinary Apps turn could wait up to 20 seconds before inference and retry again on later turns even when no remote skill was mentioned.

Caching a warning-only empty catalog preserves graceful degradation while preventing repeated synchronous discovery attempts.

Testing

• just fmt
• Tests and Clippy not run per request; CI will validate the change.

[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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

Line 300 in 78a2240

assert!(fragments.is_empty());

Add integration coverage for agent-visible skill failures

This changes agent behavior for remote discovery failures, but the updated direct extension test does not exercise the first model-request path. Please add core/suite test_codex coverage for the user-visible flow per repo guidance.

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