Add prompt-for-writes MCP tool approval mode

[kylepatel-oai]

Summary

• Add prompt_for_writes as a new MCP/app tool approval mode in config and app-server protocol schemas.
• Runtime behavior: tools with explicit read_only_hint == Some(true) skip approval; all other calls use the normal MCP approval elicitation and bypass Guardian auto-review.
• Preserve session and persistent approval keys for this mode so "allow in this chat" and "always allow" continue to work; persistent always-allow still writes a per-tool approval_mode = "approve" override.

Notes

• The generated app-server protocol fixtures in this repo are updated.
• I did not update codex-apps generated app-server-types in this PR: its mcp-codegen script currently uses the released dotslash Codex binary, while generating from this local runtime into a temp directory showed broad unrelated type churn. The runtime schema fixture here contains the new AppToolApproval value for downstream consumption.

Tests

• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-core mcp_tool_call_tests (matches 0 tests with this filter)
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-core mcp_tool_call::tests
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-core config_schema
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-mcp prompt_for_writes
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-config
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-app-server-protocol
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-app-server config_manager_service_tests (matches 0 tests with this filter)
• CARGO_NET_GIT_FETCH_WITH_CLI=true cargo test -p codex-app-server write_value_supports

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}