Lab 3 — History and sessions

Capability: Codex persists and resumes sessions. Its internal transcript and crash replay rules are not the build-your-own JSONL contract.

Install Codex CLI; create a private temporary CODEX_HOME, copy this lab’s config.toml.example to $CODEX_HOME/config.toml and fill in your endpoint (ending in /openai/v1) and deployment. Provide AZURE_OPENAI_API_KEY from your resource key via a secret manager. The Microsoft guide says Entra ID is not supported for Codex. Do not save the key in files. Workspace: start in lab03-sessions/ and follow the common preflight; no fixtures are needed. Keep the same CODEX_HOME and workspace/ for both commands, one session at a time:

codex exec --skip-git-repo-check -C "$workdir" --sandbox read-only --json `
  "Remember this synthetic order queue name: orders-demo. Say only 'noted'."
Push-Location $workdir
try {
  codex exec resume --last --json `
    "What synthetic queue name did I give you? Do not guess if it is missing."
} finally { Pop-Location }

codex exec --skip-git-repo-check -C "$workdir" --sandbox read-only --json \
  "Remember this synthetic order queue name: orders-demo. Say only 'noted'."
(cd "$workdir" && codex exec resume --last --json \
  "What synthetic queue name did I give you? Do not guess if it is missing.")

If your version’s resume selection differs, pass the thread ID from the first run’s thread.started event to codex exec resume <SESSION_ID>. Verify that the resumed answer uses prior context. Start a new codex exec session with the same question and verify it does not inherit the previous thread. Keep the two event streams private; they may include prompts and usage.

Record thread ID, whether resume worked, token usage if reported and whether the provider also persists state. Do not claim the build-your-own guarantee of replaying a crash between a tool call and its result: this lab does not inject or validate that failure.

Follow reset and cleanup afterward. A workspace reset alone does not delete the saved thread in the temporary Codex home.