Add non-null constraint to zones.number

[reteps]

Description

Add a database migration to make the number column in the zones table NOT NULL. This change has been verified to not affect production data, as no rows contain NULL values for this column. Noted in #13991.

Updates related type definitions to reflect the schema change:

• Updated ZoneSchema in db-types.ts to remove .nullable() from the number field
• Updated test fixtures to use a valid number instead of null

prairielearn=*> SELECT COUNT(*) FROM zones WHERE number IS NULL;
 count
-------
     0
(1 row)

in production

Testing

Build passes successfully with no type errors. Test fixtures updated to reflect the new constraint.

[github-actions]

All images

Image	Platform	Old Size	New Size	Change
prairielearn/executor:60d3e05ea73238616fb3ec50acac98451a13a31f	linux/amd64	1266.69 MB	1266.68 MB	0.00%
prairielearn/executor:60d3e05ea73238616fb3ec50acac98451a13a31f	linux/arm64	1234.16 MB	1234.17 MB	0.00%
prairielearn/prairielearn:60d3e05ea73238616fb3ec50acac98451a13a31f	linux/amd64	1266.68 MB	1266.68 MB	0.00%
prairielearn/prairielearn:60d3e05ea73238616fb3ec50acac98451a13a31f	linux/arm64	1234.16 MB	1234.16 MB	0.00%

No significant size changes

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR enforces a NOT NULL constraint on the zones.number column by updating the database schema definition, type definitions, migrations, and test data. The changes span schema files, two-stage database migrations, and corresponding test updates.

Changes

Cohort / File(s)	Summary
Schema and Type Definitions database/tables/zones.pg, apps/prairielearn/src/lib/db-types.ts	Modified zones.number column from nullable to NOT NULL at both the database schema and Zod validation layer.
Database Migrations apps/prairielearn/src/migrations/20260201181253_zones__number__nonnull_constraint_add.sql, apps/prairielearn/src/migrations/20260201181254_zones__number__nonnull_constraint_validate.sql	Added two-stage migration: first creates a NOT VALID CHECK constraint, then validates it, sets the column to NOT NULL, and drops the temporary constraint.
Test Updates apps/prairielearn/src/lib/client/safe-db-types.test.ts	Updated test data in MinimalStaffZone object to set number field from null to 1, reflecting the non-nullable constraint requirement.
Documentation AGENTS.md	Added Git guidance section documenting commit and rebase policies.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: adding a non-null constraint to the zones.number column, which matches the primary objective of the pull request.
Description check	✅ Passed	The description directly relates to the changeset, explaining the database migration, verifying production data safety, and documenting related type definition updates.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[nwalters512]

In other recent migrations, e.g. the pair of 20260115220136_courses__branch__nonnull_constraint_add.sql and 20260115220137_courses__branch__nonnull_constraint_validate.sql, we first added an invalid constraint, then validated it and added the NOT NULL constraint (which Postgres could immediately validate because of the existence of the other constraint). Can you say why you didn't take a similar approach here?

[reteps]

I put up sbdchd/squawk#910 so we can potentially enable this in the future

[nwalters512]

Looks like this was resolved in ff79009?

(Do we need to add "NEVER amend and force push unless specifically requested" to AGENTS.md?)

[reteps]

yes, i'll add that to this PR

[reteps]

60d3e05

[reteps]

Once we get to postgres 18 we can do this: https://neon.com/postgresql/postgresql-18/not-null-as-not-valid