Codex account-switch runtime proof

Run account-switch-driver.py SIDE CHECKOUT using Python 3. Set CODEX_PROOF_MODEL to the same supported model on both sides. Install each checkout with vp i first. Place snapshot.cjs next to the driver.

The driver launches the real T3 server and drives it with the real T3 CLI. It creates a fresh T3 home, synthetic ChatGPT auth.json, a git project, and a local HTTP backend. No real account or inference is used. It atomically replaces auth.json, waits for the actual server.getConfig provider auth snapshot to report bob@example.test, and sends a second message in the same thread. It records the decoded synthetic account identity on each backend request. The local mock returns a completed Responses stream, with the request account named in its assistant reply.

Both terminal recordings are live captures of this driver running against the respective commit, using Ghostty on Xvfb at 1600x900, same font and theme. The PNGs are final frames; pairs taken 500 ms apart were pixel-identical.

Before: b68aedfdb71534bfdfbe55771ef2e686742faa8e
After: c5c1e3adb2b1ec84d7491756f38590a35f55ce25

AI-assisted; verified with the tests and tools listed above.
