Hands-on runs and acceptance

15. Hands-on runs: verify mechanisms first, then connect a real model

All companion files live in this tutorial’s sibling demos/ directory. Local teaching demos only use the Python standard library and Node’s built-in modules. Python 3.11+ is required; this run actually used 3.14.7.

cd demos/codex-harness
python3 demos/runtime_demo.py
python3 demos/context_memory_demo.py
node demos/ptc_demo.mjs
python3 demos/computer_loop_demo.py
python3 -m unittest discover -s demos -v

15.1 What this session actually verified

Item	This run’s result	Boundary of the conclusion
Python mechanism and offline API contract tests	14 passed (9 runtime/storage + 5 API wiring)	Not Codex’s official test suite
Runtime demo	Stale plan rejected; two tools returned with a stale marker	Independent work is script-simulated, not a real LLM
Context / memory demo	History recallable, scope isolation, source revocation, and expiry flags all work	Uses fabricated structured facts, no model extraction
Local PTC demo	Outputs partial, keeps successful results, failures, and sources	Static trusted code, not a reproduction of the isolated V8 host
Local App Server probe	`initialize` succeeded	No thread was created, no model was requested
Python/JavaScript syntax checks	Passed	Does not prove online API permissions or behavior
Model API demos	Not actually called	Requires an API key, model permissions, and budget
Fake GUI loop	Local assertions pass	No real screenshots, vision model, or desktop control
Real GUI / benchmarks / post-training	Not run	Cannot claim the corresponding effects are verified

The App Server probe exited early inside a restricted sandbox on the first try. After being allowed to retry outside the sandbox, it initialized successfully. The probe process has ended and did not leave a background agent task behind.

15.2 Real App Server probe

python3 demos/app_server_client.py

It does not send thread/start or turn/start. If you want to write your own client, generate the current protocol version first:

codex app-server generate-ts --out ./schemas
codex app-server generate-json-schema --out ./schemas-json

Schema files only capture interface constraints. You still have to wire approvals, errors, notifications, and lifecycle end to end.

15.3 Real model API examples

Configure OPENAI_API_KEY in a private local environment variable. Do not put it in a tutorial or Git. This article does not read or use your API key. Once you have confirmed model and account support, you can run:

python3 demos/live_api.py direct
python3 demos/live_api.py ptc
python3 demos/live_api.py async
python3 demos/live_api.py compact

The WebSocket steering example needs ws:

npm install ws
node demos/steering_api.mjs

The API examples pin the Astra model ID gpt-6-astra from the screenshots, without silently downgrading to another model. Run each mode separately to avoid violating combination constraints such as async/PTC or steering/auto compaction. The online examples were not actually run this session. Quota, network, and API evolution can affect execution. If an unsupported field appears, check the official docs and model permissions first, and do not guess field names.

15.4 Gap between the demos and a production system

The local runtime’s job table is in memory. The event log can be persisted, but there is no implementation for crash recovery of running tasks or cross-process idempotency. Event persistence and task dispatch are also not a single atomic transaction. A production design can add an outbox, a durable job ledger, leases, and execution-state reconciliation on recovery. Cancellation only works on the demo’s asyncio coroutines. Python functions running in a ThreadPool and real OS child processes need their own termination design. The API examples show the call protocol only. They do not cover full streaming reconnection, token budget management, distributed retry, or production observability.

15.5 A learning path suitable for interview prep

Exercise	Deliverable	Acceptance
1: basic loop and layering	Draw the architecture yourself	Explain where model, tools, and execution state live
2: run the runtime demo	Read the event log	Find what happened while a tool was waiting
3: change the requirement	Construct a stale revision submission	It must be rejected
4: swap history windows	Push an error code out of the current window	Still retrievable from the archive
5: memory conflict	Add a new fact, revoke a source	Not read across projects, expired facts need re-review
6: PTC aggregation	Let one module fail	Final result marked partial, successful sources kept
7: real API	Run 10 small tasks on a fixed model	Log requests, tool results, cost, and failure reasons
8: fair comparison	Compare serial and concurrent on the same model	Correctness does not regress before you discuss latency gains

Guides

Codex and Harness

Hands-on runs and acceptance

15. Hands-on runs: verify mechanisms first, then connect a real model

15.1 What this session actually verified

15.2 Real App Server probe

15.3 Real model API examples

15.4 Gap between the demos and a production system

15.5 A learning path suitable for interview prep

​15. Hands-on runs: verify mechanisms first, then connect a real model

​15.1 What this session actually verified

​15.2 Real App Server probe

​15.3 Real model API examples

​15.4 Gap between the demos and a production system

​15.5 A learning path suitable for interview prep

15. Hands-on runs: verify mechanisms first, then connect a real model

15.1 What this session actually verified

15.2 Real App Server probe

15.3 Real model API examples

15.4 Gap between the demos and a production system

15.5 A learning path suitable for interview prep