Make context contributors async

[jif-oai]

Summary

• make ContextContributor return a boxed Send future
• await context contributors during initial context assembly
• update existing contributors and extension-api examples for the async contract

Testing

• cargo test -p codex-extension-api --examples
• cargo test -p codex-git-attribution
• cargo test -p codex-core build_initial_context_includes_git_attribution_from_extensions -- --nocapture
• cargo test -p codex-core build_initial_context_omits_git_attribution_when_feature_is_disabled -- --nocapture
• cargo test -p codex-core (fails in unrelated agent::control::tests::spawn_agent_fork_last_n_turns_keeps_only_recent_turns stack overflow)
• just fix -p codex-extension-api
• just fix -p codex-git-attribution
• just fix -p codex-core
• cargo clippy -p codex-extension-api --examples

[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

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[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".