chore: introduce ConversationManager as a clearinghouse for all conversations

[bolinfest]

This PR does two things because after I got deep into the first one I started pulling on the thread to the second:

• Makes ConversationManager the place where all in-memory conversations are created and stored. Previously, MessageProcessor in the codex-mcp-server crate was doing this via its session_map, but this is something that should be done in codex-core.
• It unwinds the ctrl_c: tokio::sync::Notify that was threaded throughout our code. I think this made sense at one time, but now that we handle Ctrl-C within the TUI and have a proper Op::Interrupt event, I don't think this was quite right, so I removed it. For codex exec and codex proto, we now use tokio::signal::ctrl_c() directly, but we no longer make Notify a field of Codex or CodexConversation.

Changes of note:

• Adds the files conversation_manager.rs and codex_conversation.rs to codex-core.
• Codex and CodexSpawnOk are no longer exported from codex-core: other crates must use CodexConversation instead (which is created via ConversationManager).
• core/src/codex_wrapper.rs has been deleted in favor of ConversationManager.
• ConversationManager::new_conversation() returns NewConversation, which is in line with the new_conversation tool we want to add to the MCP server. Note NewConversation includes SessionConfiguredEvent, so we eliminate checks in cases like codex-rs/core/tests/client.rs to verify SessionConfiguredEvent is the first event because that is now internal to ConversationManager.
• Quite a bit of code was deleted from codex-rs/mcp-server/src/message_processor.rs since it no longer has to manage multiple conversations itself: it goes through ConversationManager instead.
• core/tests/live_agent.rs has been deleted because I had to update a bunch of tests and all the tests in here were ignored, and I don't think anyone ever ran them, so this was just technical debt, at this point.
• Removed notify_on_sigint() from util.rs (and in a follow-up, I hope to refactor the blandly-named util.rs into more descriptive files).
• In general, I started replacing local variables named codex as conversation, where appropriate, though admittedly I didn't do it through all the integration tests because that would have added a lot of noise to this PR.

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• feat: support traditional JSON-RPC request/response in MCP server #2264
• fix: update OutgoingMessageSender::send_response() to take Serialize #2263
• -> chore: introduce ConversationManager as a clearinghouse for all conversations #2240

[github-actions]

Summary

• Introduces ConversationManager and CodexConversation to manage conversations; removes CodexWrapper and ctrl-c plumbing in core. Updates CLI and server code to use the new abstractions.

Notes

• New error variants added for conversation lookup and first-event validation.
• Ctrl-C handling moves from Notify tokens to tokio::signal::ctrl_c() usage.
• Tests and exports updated to reflect new types.

Review
Overall, this is a clean API refactor toward a conversation-centric model. A few polish and safety suggestions:

• codex-rs/cli/src/proto.rs

  • At L36–L43: Consider surfacing session_configured info or logging it to preserve prior UX parity. It’s currently constructed then dropped.
  • At L52 and L89: tokio::signal::ctrl_c() returns a Result—use _ = tokio::signal::ctrl_c() => is fine, but ensure other branches don’t swallow errors. Optionally log on interrupt for user feedback.
  • At L66: Error message uses {e:?}; prefer {e} unless Debug carries needed context.

• codex-rs/core/src/codex.rs

  • At L572: abort is now private. Verify no external callers relied on it; otherwise document new shutdown behavior.
  • At L717: Removing interrupt-driven cancellation means long-running execs only stop when the channel closes. If intentional, add a short comment on rationale, since SIGINT now only affects top-level loops.
  • At L154: Spawned task no longer receives a cancel signal; consider a graceful shutdown path on Drop or a channel close comment for maintainers.

• codex-rs/core/src/codex_conversation.rs

  • New wrapper is thin and good. Consider deriving Clone for CodexConversation if it’s meant to be held by Arcs across layers (saves re-wrapping patterns later).

• codex-rs/core/src/conversation_manager.rs

  • At L36–L43: Nice first-event validation. The dedicated SessionConfiguredNotFirstEvent error is clear.
  • At L61–L69: Stores conversations in a RwLock<HashMap<Uuid, Arc<_>>>. Consider a DashMap if contention grows, but RwLock is fine to start.
  • At L83–L96: get_conversation returns CodexErr::ConversationNotFound(id); great. Consider adding a remove_conversation for lifecycle cleanup.

• codex-rs/core/src/error.rs

  • New variants look good; ensure error enum ordering remains roughly grouped by domain.

• codex-rs/core/src/exec.rs

  • At L363: Switched to tokio::signal::ctrl_c() inside consume_truncated_output. That globally traps SIGINT per task; be mindful if multiple execs run concurrently. An alternative is a per-call cancellation primitive passed in, but this might be acceptable.

• codex-rs/core/src/lib.rs

  • Export changes are consistent. Removing codex_wrapper is the right call given ConversationManager.

• codex-rs/mcp-server/src/conversation_loop.rs

  • Type change to Arc<CodexConversation> looks consistent. Check other handlers similarly updated.

Follow-ups (outside this PR scope)

• Provide a minimal example in docs showing ConversationManager usage.
• Add a shutdown API on ConversationManager to drop conversations and signal background tasks.

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