Codex App: subagent Last Turn diff drops the initial implementation after a follow-up

What version of the Codex App are you using (From “About Codex” dialog)?

26.820.7780.0

What subscription do you have?

Unknown (signed in with a ChatGPT account; the plan is not exposed in the task context)

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

When a primary agent delegates implementation to a subagent and later sends a follow-up instruction to that same subagent, the Codex App's Last Turn review shows only the diff produced by the final follow-up.

The earlier, substantive implementation from the same delegated subagent task disappears from the review scope, even though those edits remain in the working tree.

In the reproduced case:

• The subagent's first pass implemented a functional refactor across 11 files.
• The primary agent then sent a follow-up asking only for whitespace cleanup.
• The follow-up changed formatting in a small subset of those files.
• Last Turn showed only the whitespace cleanup, not the functional implementation that the subagent interaction produced.

This makes the review misleading: the visible diff suggests the delegated task only changed whitespace, while most of its actual edits are hidden from that review surface. Switching to an ordinary working-tree diff is not equivalent because it can include unrelated edits and loses subagent-task attribution.

What steps can reproduce the bug?

1. Open a Git repository in Codex App.
2. Ask the primary agent to spawn a subagent for an implementation task.
3. Let the subagent complete an initial turn that edits multiple files.
4. Have the primary agent send a follow-up task to the same subagent, such as a small whitespace cleanup.
5. Let that follow-up complete.
6. Open the Review panel and select Last Turn, or open the changes associated with the completed delegated work.
7. Observe that only the final follow-up's small diff is shown; the initial implementation diff from the same subagent task is absent.

What is the expected behavior?

Reviewing a completed delegated subagent task should show the cumulative diff produced across all turns in that subagent interaction.

If Last Turn must remain strictly turn-scoped, the UI should distinguish between:

• Latest subagent turn
• Entire delegated task

Clicking the completed subagent interaction should default to the entire delegated-task diff so a cleanup follow-up cannot hide the main implementation.

Additional information

The edits are not lost from disk; this is a review-boundary and attribution problem.

Related but not duplicate:

• #17963 reports missing files from a single most-recent turn.
• #40830 reports a historical turn showing a different worktree's newer diff.
• This report concerns multiple turns within one delegated subagent task, where a follow-up replaces the substantive initial pass in the visible review scope.

Start by reproducing the delegated subagent flow and inspect the Review panel's Last Turn diff selection and subagent-task attribution. Trace how changes from the initial and follow-up turns are collected, then verify that the completed delegated task shows its cumulative diff while a latest-turn view remains distinguishable if retained.