[clinic · EX-09] Survive an encoder upgrade

[akash-coded]

Exercise clinic. One long-running thread per exercise. Ask here rather than opening a
new thread — the answers accumulate where the next person will look for them.

Exercise: EX-09 — Survive an encoder upgrade · difficulty 🔴

What this exercise asks

Read the exercise first; this thread is for when you are stuck, not instead of it.

Three ways people get stuck on this one

1. Writing new vectors into the existing version. A mixed-encoder index returns well-formed numbers for vectors that mean nothing to each other, and nothing errors.

2. Comparing before and after on different eval slices.

3. Declaring success on aggregate recall without checking per-class — an encoder swap usually helps some classes and hurts others.

How to ask here

Post the numbers you got, the config that produced them, and what you already tried.
A question with a measurement in it gets answered in one round trip; a question without one
takes three.

If you have finished it, post the write-up in Show and Tell with the
[solution · EX-09] prefix rather than here — this thread stays for people who are stuck.