Write down the stacked-PR rule that has stranded work twice

CLAUDE.md

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+# Working in this repository
+
+## Verify before pushing
+
+Three commands, all of which must pass:
+
+```
+npm run lint                        # banned phrases, heading rules, figure and chapter-reference rules
+node scripts/check-figure-geometry.mjs   # renders every SVG in Chromium: text overlap, arrowheads, coin marks
+npm run build-pdf                   # the whole book, and the page count is a useful smell test
+```
+
+`npm run preview -- <chapter> "<phrase>"` renders a single chapter around a phrase, which is faster than
+building the book when checking one edit.
+
+## Stacked pull requests
+
+A stacked PR is one whose base is another PR's branch rather than `main`. They have stranded work here
+twice, and the failure is silent: GitHub reports every PR in the stack as merged while none of the
+content reaches `main`.
+
+The mechanism: once the parent PR merges, its branch is dead. Merging the child into that dead branch
+puts the work somewhere nobody will merge from again. A grandchild stacked on the child inherits the
+same fate.
+
+**Retarget the child onto `main` as soon as the parent merges, and before merging the child.** Do not
+merge a PR whose base branch has already merged.
+
+**After any merge, verify the work actually landed** rather than trusting the merged badge:
+
+```
+git fetch origin --prune
+git merge-base --is-ancestor origin/<branch> origin/main && echo "landed" || echo "STRANDED"
+```
+
+Prefer a flat PR off `main` whenever the work is separable. Stack only when the child genuinely cannot
+be reviewed or built without the parent.
+
+## Naming things the companion repository owns
+
+Prose must never name a field, function, or error that does not exist in
+`quicknode/solana-program-examples`. When renaming an identifier, the companion repository changes
+first and this repository follows, so the book never describes a name that was never shipped. Grep both
+repositories before and after: no occurrence of the old name should survive here, and every new name
+should resolve to a real definition there.
+
+## Writing
+
+`WRITING-PLAN.md` holds the house style and the conventions the linter enforces. Read it before editing
+prose.