## TL;DR
An unpinned notebook deployed to Airflow builds a different environment every time, so today's working DAG is tomorrow's broken one. Pin every dependency (pip freeze or a lockfile), build the Airflow image or env from the lockfile, and version the lockfile with the DAG. The agent's deploy step should refuse to ship without a lockfile. Reproducibility is the deploy requirement, not a nice-to-have.

```text
agent deployed the notebook to airflow without pinning dependencies, build failed
```

## Use this when
- An Airflow-deployed notebook fails with dependency errors that did not occur in dev.
- Rebuilds produce different environments.
- The deploy has no requirements file or lockfile.

## Not for this skill when
- The DAG code itself is broken. That is a DAG bug.
- Pinned builds still fail. That is a genuine incompatibility.

## Steps
1. Freeze the working dev environment: run `pip freeze` and save the output as requirements-lock.txt. Verify: the file pins every package.
2. Add the lockfile to the deploy (image build or env creation). Verify: the build consumes the lockfile.
3. Rebuild from scratch and run the notebook. Verify: the scheduled run matches dev.
4. Version the lockfile alongside the DAG. Verify: rollbacks restore the env too.
5. Gate the agent's deploy: no lockfile, no deploy. Verify: the gate fires on a test unpinned deploy.

## Variant phrasings
### airflow notebook dependencies not pinned
Short form. Lockfile or it did not happen.

### notebook deploy airflow build failed
The symptom phrasing. Pin, then rebuild.

### unpinned deps scheduled notebook
General phrasing. Reproducibility is the requirement.

Compatibility: Airflow 2.x, pip/conda. Lockfiles work with any builder.

## Why it happens
Unpinned installs resolve to 'latest' at build time, and latest moves: a numpy 2 release, a removed API, a yanked wheel. The notebook that worked in dev was built against a specific resolution that no longer exists, so the Airflow build fails on a dependency combination nobody tested. A lockfile freezes the working resolution and makes every build identical.

## Edge cases / pitfalls
- `pip freeze` captures everything, including dev-only tools. Curate or use a proper locker (pip-tools, poetry).
- The lockfile must match the python version too. A 3.11 lockfile on a 3.10 image breaks.
- Native dependencies (system libs) also need pinning in the image. The lockfile covers python only.
- Review lockfile diffs on update like code. A major bump deserves a test run.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_3BO1C0MGrevG_Rl4MVijBg