chore(otel): reorganize codex-otel crate

[owenlin0]

Summary

This is a structural cleanup of codex-otel to make the ownership boundaries a lot clearer.

For example, previously it was quite confusing that OtelManager which emits log + trace event telemetry lived under codex-rs/otel/src/traces/. Also, there were two places that defined methods on OtelManager via impl OtelManager (lib.rs and otel_manager.rs).

What changed:

• move the OtelProvider implementation into src/provider.rs
• move OtelManager and session-scoped event emission into src/events/otel_manager.rs
• collapse the shared log/trace event helpers into src/events/shared.rs
• pull target classification into src/targets.rs
• move traceparent_context_from_env() into src/trace_context.rs
• keep src/otel_provider.rs as a compatibility shim for existing imports
• update the codex-otel README to reflect the new layout

Why

lib.rs and otel_provider.rs were doing too many different jobs at once: provider setup, export routing, trace-context helpers, and session event emission all lived together.

This refactor separates those concerns without trying to change the behavior of the crate. The goal is to make future OTEL work easier to reason about and easier to review.

Notes

• no intended behavior change
• OtelManager remains the session-scoped event emitter in this PR
• the otel_provider shim keeps downstream churn low while the internals move around

Validation

• just fmt
• cargo test -p codex-otel
• just fix -p codex-otel

[owenlin0]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: b3f493326e

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".

[chatgpt-codex-connector]

Preserve legacy traces module re-export

lib.rs no longer exports pub mod traces, and src/traces/mod.rs was removed. Downstream imports like codex_otel::traces::otel_manager::{OtelManager, OtelEventMetadata, ToolDecisionSource} will now fail to compile. That is a public API break despite the stated compatibility/no-behavior-change intent; add a shim module that re-exports the moved items.

Useful? React with 👍 / 👎.