add lesson about references

Author: efrymire

observablehq.config.js

@@ -14,6 +14,7 @@ export default {
         { name: "Intro to Web Development", path: "/lessons/1_intro_to_web_development" },
         { name: "Working in Cursor", path: "/lessons/2_working_in_cursor" },
         { name: "Intro to Observable Framework", path: "/lessons/3_intro_to_observable_framework" },
+        { name: "Confirming Spring Upstream", path: "/lessons/4_confirming_spring_upstream" },
         // { name: "Intro to Observable Plot", path: "/lessons/4_intro_to_observable_plot" },
       ]
     },

src/lessons/4_confirming_spring_upstream.md

@@ -0,0 +1,90 @@
+---
+title: Confirming Spring Upstream
+toc: true
+---
+
+# Confirming Spring Upstream
+
+---
+
+You may have some references to the Fall 2025 repository -- and my apologies for not replacing the link when including the git instructions. The instructions are updated, but the following includes specific instructions for each circumstance. 
+
+There are two scenarios you could fall into:
+1. **You forked the Fall repo**, or
+2. **Your upstream is the Fall repo**. 
+
+You can determine if you fall into either of these scenarios from the following steps. 
+
+**Check your repo name.** It should be `Interactive-Data-Vis-Spring2026`. If the reference is `-Fall2025`, follow instructions for [forking the correct repo](#if-you-forked-the-fall-repo).
+
+**Check your remote repository links.** You can do so by navigating to the project folder in your terminal and running: 
+
+```sh
+git remote -v
+```
+
+You should see both your origin and upstream remotes. Example:
+
+```text
+origin    https://github.com/[YOUR_USERNAME]/Interactive-Data-Vis-Spring2026.git (fetch)
+origin    https://github.com/[YOUR_USERNAME]/Interactive-Data-Vis-Spring2026.git (push)
+upstream  https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026.git (fetch)
+upstream  https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026.git (push)
+```
+
+If your upstream is not there, **or it references the old repo** at `https://github.com/InteractiveDataVis/Interactive-Data-Vis-Fall2025.git`, you'll need to re-do the upstream via [the instructions below](#if-your-upstream-is-the-fall-repo). 
+
+Once you're done, you can pull Lab 1 into your fork. And I promise, no fall references this time...
+
+---
+
+## If you forked the Fall repo
+
+This does require a complete re-forking of the appropriate repo to include all the details you will need for this semester.
+
+You should first fork the appropriate repo before archiving the incorrect fork. That way, you can copy the work you've already done for Lab 0.
+
+1. Follow the instructions in the [Lab 0 readme](https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026/tree/main/src/lab_0) to fork the correct repo. You probably already have all the installations if you completed them before. 
+2. Confirm your upstream is correct by continuing to the following steps:
+
+---
+
+## If your `upstream` is the Fall repo
+
+Your fork of the class repo should stay connected to the correct Spring 2026 class repository. That way you can pull new labs, fixes, and content when I update the repo.
+
+You should be able to push and pull from your origin, as well as pull new content from the class repo. 
+
+- **`origin`** → your fork (e.g. `https://github.com/[YOUR_USERNAME]/Interactive-Data-Vis-Spring2026.git`)
+- **`upstream`** → the class repo: `https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026.git`
+
+If **`upstream`** is missing, add it:
+
+```sh
+git remote add upstream https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026.git
+```
+
+If **`upstream`** already exists but points to the wrong URL, update it instead:
+
+```sh
+git remote set-url upstream https://github.com/InteractiveDataVis/Interactive-Data-Vis-Spring2026.git
+```
+
+Then run `git remote -v` again to confirm.
+
+For the full GitHub setup (fork, clone, upstream, Pages, and syncing), see [Lab 0: Getting Started](/lab_0/readme).
+
+---
+
+## Pulling Released Labs
+
+After your upstream points to the Spring 2026 repo, pull the latest content (including Lab 1) into your local copy:
+
+```sh
+git fetch upstream
+git merge upstream/main
+```
+
+Do this from your project folder, ideally before you start new work. If you have uncommitted changes, commit or stash them first (commit = [save changes to the repo](https://docs.github.com/en/pull-requests/committing-changes-to-your-project); stash = [temporarily set them aside](https://docs.github.com/en/desktop/making-changes-in-a-branch/stashing-changes-in-github-desktop)). After merging, you should see the `lab_1` folder and any other updates from the class repo.
+
+You can repeat these two steps every time a new lab is released.