Whole-Ad Product Swap: Deterministic Planning First, Model Only Where Forced

Variant Multiplier already let an editor swap one section of a winning ad and keep the rest. The next request from a real production job — replacing product SL-603 with SL-808, a different hearing-aid SKU, across an entire finished ad — was a different shape of problem. It's not "change one section," it's "change every mention of the product, everywhere it appears, while keeping literally everything else the same." Two direct quotes from the editor drove the whole five-PR arc: the transcript editing was too rigid for word-by-word changes, and separately, "the music, voice, etc. should retain the same, we should keep the quality the same, and not make it do a lot of changes." If a re-render can degrade something the editor explicitly asked to keep untouched, the render path is wrong for the job — no matter how good the model is. The cheap fix first: let editors actually edit PR #67 shipped before any product-swap work started, because it was the cheap, high-value half of the same feedback: "I am just able to select word by word here but I am not really able to change the whole sentence a lot easier," and separately, "I'm able to double click on these words and then just type it in." Both were UI gaps in the transcript editor, not pipeline gaps — selecting by sentence or scene instead of only by word, and retyping a line verbatim instead of only substituting individual words. Shipping this first, standalone, meant the harder product-swap work that followed didn't also have to carry an unrelated UX fix in its diff. A product catalog the tool never had PR #69, stacked directly on top of the transcript work, is pure groundwork with no user-visible feature of its own: a product catalog, because Variant Multiplier had no concept of "a product" at all before this. The editor's own framing made the requirement explicit: "have a product selection right here, for Pro Bluetooth, for [the other SKU], and maybe other tons of products" going forward. The catalog data itself is mai