A touchstone is a piece of dark stone. You rub gold against it, you look at the streak it leaves, and you compare that streak to a set of reference needles of known purity. The stone does not know what the market pays for gold, and it does not care whether you are buying or selling. It tells you what the metal is. That is the whole design brief for this app, and the reason a quest about market data can be about restraint rather than about signals.
You will start with the boundary: what the product is, the four things it deliberately is not, and where it sits among its siblings — a portfolio app upstream that owns the holdings, a workshop pattern it borrowed for heavy analysis, and a required Pippa surface it talks to. Then the ethic rendered as architecture, which is the interesting part: not a disclaimer at the bottom of a page, but a set of engineering choices where a function returns a characterization instead of a call, a sorted list is documented as an ordering rather than a ranking, and the thing that makes a raw number meaningful is percentile context rather than a threshold that shouts.
The middle of the quest is five separate ways to be dishonest with a number, each one drawn from something that actually went wrong. A snapshot stamped with the machine's calendar instead of the market's, in an app whose daily job runs at an hour when three markets disagree about what day it is. A percentile printed without the window it was measured against, when the windows in question run from three years to a century and a half. A fetch that truncated in a way that reads exactly like success, until you notice the ten largest companies in America do not include the largest company in America. A standard held so high in one corner of the product that the feature stalled for a day, while the rest of the product had been shipping a stated approximation the whole time. And a model that computed the headline number in a browser, where no command line, no delegation brief and no assistant could ever read it, and where it left no trace of where the needle had been.
It closes on the fix that ties those together — numbers get one home, words get another — and on the queue that runs the heavy work, where pipelines are database rows instead of a code registry so a new kind of analysis can be designed in conversation instead of in a deploy. Conceptual open-sourcing: the architecture is the deliverable, not a repository you clone.