[3/8] Add pushed exec process events

[aibrahim-oai]

Summary

• Add a pushed ExecProcessEvent stream alongside retained process/read output.
• Publish local and remote output, exit, close, and failure events.
• Cover the event stream with shared local/remote exec process tests.

Testing

• cargo check -p codex-exec-server
• cargo check -p codex-rmcp-client
• Not run: cargo test per repo instruction; CI will cover.

Stack

o  #18027 [8/8] Fail exec client operations after disconnect
│
o  #18025 [7/8] Cover MCP stdio tests with executor placement
│
o  #17974 [6/8] Wire remote MCP stdio through executor
│
o  #17987 [5/8] Add executor process transport for MCP stdio
│
o  #17986 [4/8] Abstract MCP stdio server launching
│
@  #18020 [3/8] Add pushed exec process events
│
o  #17985 [2/8] Support piped stdin in exec process API
│
o  #17984 [1/8] Add MCP server environment config
│
o  main

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Buffer events until first subscriber attaches

SessionState::new creates a broadcast channel and immediately drops the initial receiver. If a short-lived process outputs/exits before subscribe_events() is called, publish_event drops those events (no receivers), yet the sender remains alive on the process handle. An event-only consumer can then wait forever for Exited/Closed, which is a functional hang.

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[chatgpt-codex-connector]

Keep session routed until ordered terminal events arrive

On exec/closed, the client removes the session before forwarding the event. Server notifications are emitted from concurrent tasks, so closed can arrive before lower-seq exited/output notifications. After removal, those delayed notifications are dropped, so remote event subscribers can miss exit status or tail output.

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