printedparts lab: set expectations up front

State that this is a bundled plugin whose frontend and three small core
edits land in this repo, list the three deliberate divergences from the
scaffold before the learner hits them, suggest a per-milestone solution
branch for instructors, and point out the earliest visible win (wire
the bare list page as soon as the GET endpoint works).

docs/PLUGIN-LAB-PRINTEDPARTS.md

@@ -17,6 +17,24 @@ Ground rules
 - DB columns: lowercase concatenated (`quantityonhand`, not quantity_on_hand).
 - Run `bash scripts/check-naming-and-style.sh` and the test suite at every
   checkpoint.
+- Commit once per milestone. Working on a branch is fine; so is a fork.
+
+Know before you start
+- You are building a BUNDLED plugin inside this repo. Plugin frontend files
+  live in core (`frontend/src/...`), and three core files get small edits:
+  `frontend/src/api/index.js` (api client), the router, and
+  `PLUGIN_TABLE_OWNERS` in `shopdb/plugins/alembic_template.py`. That is
+  normal for all 12 bundled plugins - external-plugin UI packaging does not
+  exist yet - so do not be confused when a "plugin" touches core.
+- This plugin deliberately DIVERGES from the scaffold in three places, each
+  a teaching point you will hit in order: (1) it is NOT an asset type, so the
+  scaffold's AssetType seeding gets deleted (M1); (2) its migration is a REAL
+  baseline that creates tables, not a stamp-only anchor (M1); (3) its kiosk
+  take endpoint is the product's first UNauthenticated write - read the
+  decision record in the proposal before building it (M4).
+- Instructor option: keep a solution branch with one commit per milestone
+  (tag `lab-m1`..`lab-m7`); a stuck learner can `git diff lab-m3 lab-m4` to
+  see exactly what a milestone changes.
 
 ---
 
@@ -71,6 +89,12 @@ Build
 5. Seed the 3 settings in `on_install` (Setting.set pattern - see how other
    plugins seed in `on_install`; category `printedparts`).
 
+Tip - earlier visible win: as soon as the GET list endpoint works, jump ahead
+and wire just the api client + router entry + a bare `PrintedItemsList.vue`
+(first two steps of M3), seed two rows by hand, and look at your parts in the
+browser. Everything before that moment is invisible; seeing the table makes
+the rest of the lab concrete. Then come back and finish the mutations here.
+
 Checkpoint
 ```
 pytest plugins/printedparts/tests/ -q      # write tests as you go: