Correction: Fan-out join

Sharpened the wording on Fan-out join after someone pointed out it was overstated.

The original read as though the pattern always applies. It does not. A join to a table with more than one row per key multiplies every measure on the other side. Nothing errors, and the number is plausible.

What it should have said — and now does — is where it stops applying. Every technique has a range of validity, and a pattern library that states rules without stating their limits produces exactly the cargo-culting it was meant to prevent.

The revised page names the case where the simple version is fine, so you are not paying the cost of the careful version on a table with four rows.

Corrections go in the page, with a note about what changed. No silent edits. The course will contain errors — it is thirty-six lessons about a field where the standard advice is frequently wrong — and the only defensible approach is to fix them visibly.

The repository takes issues, and several pattern pages are sharper than what we shipped because someone argued.