V2 session revert can race with session execution

[PrisonBreakPB]

Description

A V2 session can resume or wake its runner while a revert is staged.
This can allow model execution to continue before the revert is committed or cleared.

Plugins

No response

OpenCode version

dev (f557328)

Steps to reproduce

1. Start a V2 session with an active execution.
2. Stage a revert for a session message.
3. Wake or resume the session before committing or clearing the revert.
4. Observe that the runner may continue while the revert remains staged.

Screenshot and/or share link

No response

Operating System

Windows 11

Terminal

No response

[CasualDeveloper]

I confirmed this problem on current v2.

One failing case happens when a user undoes a message, edits it, and sends the edited message again. The server can start saving the new message before it has finished saving the undo. The two operations can then happen in the wrong order.

#37752 tried to solve this by processing these changes one at a time. GitHub closed that PR automatically because it became old. It was not closed because maintainers rejected the approach.

My branch finishes that approach. For each session, OpenCode finishes one undo or message change before starting the next one. The branch also loads plugins before blocking other session changes. This prevents a freeze when plugin setup sends a message of its own.

I added tests for successful replacements, failed replacements, retries, and requests that happen at the same time. The work currently depends on #42461.

If maintainers still want this fix, I can update the branch after #42461 is resolved and open a focused PR that closes this issue.