Responses streams need lifecycle diagnostics for close, timeout, and partial-output failures

What version of Codex is running?

Current main as of 2026-04-27.

What issue are you seeing?

When a Responses stream closes, errors, or idles before response.completed, Codex reports the failure but does not expose enough lifecycle evidence to diagnose where the stream died.

Today a stream that never produced meaningful output and a stream that reached response.output_item.added or response.output_item.done can collapse into a similar operator-visible failure shape. That makes it hard to distinguish:

• provider silence before first event
• connection loss after response.created
• an early stall after response.output_item.added
• a later stall after durable output started
• close-before-completion after partial assistant output
• response-id correlation problems between created and completed events

Why this matters

These cases need different follow-up behavior. Some are plain stream failures, some are partial-output failures, some are retry/resume candidates, and some may indicate a transport-specific issue.

Without lifecycle diagnostics, downstream retry/fallback bugs are harder to debug and issue reports have to rely on private logs or manual transcript forensics.

Expected behavior

For Responses SSE/WebSocket stream completion and failure paths, Codex should record structured lifecycle evidence such as:

• request attempt sequence
• transport path or transport reason
• created response id
• completed response id, if any
• first event elapsed time
• last event elapsed time
• last event kind
• first response.output_item.added elapsed time, if any
• first response.output_item.done elapsed time, if any
• first response.output_text.delta elapsed time, if any
• observed stream event kinds
• stream event count
• terminal stream state: completed, closed before completion, idle timeout, or stream error

This would make close-before-completion and idle-timeout reports actionable without changing retry or fallback policy.

Non-goals

This issue is not asking Codex to:

• shorten the default stream idle timeout
• switch to HTTP fallback after a particular event pattern
• change retry budgets
• change model behavior

The ask is diagnostics only: expose enough stream lifecycle evidence that the correct retry/fallback policy can be reasoned about separately.

Minimal validation shape

A useful test suite would cover:

1. completed stream: records created/completed response id and terminal state completed
2. close before response.completed: preserves the ordinary error and records the last observed event kind
3. idle timeout before any event: records no first event and terminal state idle_timeout
4. idle timeout after response.output_item.added: records the first output-item-added timing and terminal state idle_timeout
5. idle timeout after durable output: records first output-item-done and/or first text-delta timing separately from the early-output case