presentations

# Presentations Two paths produce a PPTX, and picking the wrong one destroys work. Choose first, then follow that path's section, and finish with the validation section — it applies to both. ## Which path - **An existing `.pptx` is in play** — a template, a deck the user uploaded, a prior version of this deliverable, a downloaded starting point — **edit it in place** with the XML pipeline below. Always. The edit path is Python + the bundled helpers; it does not need Node. - **Nothing exists yet and there is no template** — generate a **new** deck. Prefer **pptxgenjs** when Node and npm are actually usable; fall back to **python-pptx** when they are not. Detect before you write the generator (see below) — do not assume either runtime from the skill name alone. **Never rebuild an existing deck to apply a change.** Regenerating a deck re-authors every slide: the master, theme, fonts, colors, logos, footers, and every slide you did not think to re-emit are gone, silently, and the user sees a deck that no longer looks like theirs. A one-line text fix is a one-line XML edit, not a rewrite. Equally, never recreate from scratch what a template already provides — if the user handed you a template, its design *is* the requirement. ## New decks: detect the runtime first Before writing a generator, decide Node vs Python carefully. Do not spend turns on `npm install` or a pptxgenjs script when `node`/`npm` are truly missing — that is how runs burn steps and then redo the...