PR: https://git.cafe/pingdotgg/t3code/pulls/29228
PR head: 3d67cc1ef62657f778a979122ac5625e5bbced38
Before: github/main 55e2538561
Linux VM; /usr/bin/google-chrome; repository Playwright 1.60.0.
One background dev server at a time; main stopped before PR started.
Data: real repo created by a gpt-6.1-sol turn in the app; project added in web UI.

MAIN
node apps/server/src/bin.ts thread start --base-dir /home/user/main/.t3 --provider codex --model gpt-6.1-sol --worktree main --branch feature/taken --title "Taken branch launch" --json /home/user/worktree-verification "Run pwd, git branch --show-current, git rev-parse HEAD, and cat base.txt. Report the results. Do not edit files."
Result: Workspace preparation failed during provision worktree: Git command failed in GitVcsDriver.createWorktree.createBranch (/home/user/worktree-verification): git worktree add failed (branch_already_exists)
Clicked Retry in web UI: same error.

PR (same command, base-dir /home/user/t3code/.t3)
Result: completed; branch feature/taken-1.
Provider output:
$ pwd
/home/user/t3code/.t3/worktrees/worktree-verification/feature-taken-1
$ git branch --show-current
feature/taken-1
$ git rev-parse HEAD
78fb00518f501361e7cf63671f21409ba45dfcd0
$ cat base.txt
base on main

MCP PATH
Sent a web UI message to the same Codex gpt-6.1-sol thread requesting two concurrent t3_thread_launch calls:
workspaceStrategy={type:"worktree",baseRef:"main",branch:"feature/taken",startFromOrigin:false}
Launches accepted 2026-11-02T22:52:00.580Z and 2026-11-02T22:52:00.762Z.
Collision A completed on feature/taken-2; Collision B completed on feature/taken-3.
Each provider ran pwd, git branch --show-current, git rev-parse HEAD, cat base.txt in its own worktree.
Both HEADs: 78fb00518f501361e7cf63671f21409ba45dfcd0; both read "base on main".

NEIGHBOR
Fresh launch with --branch feature/fresh completed with its exact requested branch and same base commit.

READ-ONLY GIT INSPECTION
78fb00518f501361e7cf63671f21409ba45dfcd0 refs/heads/feature/fresh
fb1b7761b563cd4ba57ab536d72e613f57519802 refs/heads/feature/taken
78fb00518f501361e7cf63671f21409ba45dfcd0 refs/heads/feature/taken-1
78fb00518f501361e7cf63671f21409ba45dfcd0 refs/heads/feature/taken-2
78fb00518f501361e7cf63671f21409ba45dfcd0 refs/heads/feature/taken-3
78fb00518f501361e7cf63671f21409ba45dfcd0 refs/heads/main
branch.feature/taken-1.t3-merge-base main
branch.feature/fresh.t3-merge-base main
branch.feature/taken-2.t3-merge-base main
branch.feature/taken-3.t3-merge-base main