bi-03 step 02 — Observe, then build the tree builder

Goal

Establish the browser as the oracle, then write a tree builder that agrees with it.

Capture the oracle. Open each fixture from file:// in Chrome, paste src/show.js into the console, and save the output to src/observed/<case>.txt. Keep exact whitespace.
Score your predictions honestly: exact / structurally right, details wrong / wrong.
Write src/foster.js, exporting buildTree(tokens). Under ~80 lines, no dependencies. Implement only: a stack of open elements, the inBody and inTable insertion modes, an appropriateInsertionPlace(fosterParenting) function, and the <input type=hidden> exception.

Run the harness.

node run.mjs a       # your output
node check.mjs       # diff against the browser

Cases a, b, d must pass exactly. Case c is the stretch goal.

If you attempt case c, do not fix the diff blindly. Read it: it is telling you precisely what the in-table-text character sub-mode is for.

All four observed files captured
Predictions scored
node check.mjs passes cases a, b, d
You can explain why case A's world text lands inside the div and not before the table