Update to Headcount: Technology

{
  "description": "Designs system structure and makes architectural decisions defensible — boundaries, coupling, trade-offs, and recording why. Use this to design a new system or major component, choose between architectural options, review an existing design, decide where a boundary belongs, or document an architectural decision so it survives the people who made it.",
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  "name": "solution-architecture",
  "skill_md_contents": "---\nname: solution-architecture\ndescription: Designs system structure and makes architectural decisions defensible — boundaries, coupling, trade-offs, and recording why. Use this to design a new system or major component, choose between architectural options, review an existing design, decide where a boundary belongs, or document an architectural decision so it survives the people who made it.\n---\n\n# Solution architecture\n\nArchitecture is the set of decisions that are expensive to reverse. Everything cheap to change later\nis design, and does not need this level of ceremony.\n\n## Start from what constrains, not from what appeals\n\nArchitecture is driven by quality attributes, not by features. Establish the ones that actually bind\nbefore drawing anything: expected load and its shape, latency the user notices, availability the\nbusiness will fund, data residency and retention obligations, the rate of change the team needs to\nsustain, and the size and skills of the team who will operate it.\n\nVague attributes produce vague architecture. \"Scalable\" is not a requirement; \"20,000 concurrent\nsessions with p99 under 300ms\" is a constraint that eliminates options.\n\n## Boundaries are the whole game\n\nDraw boundaries where change is independent and where data has a single owner. A boundary in the\nright place absorbs change; a boundary in the wrong place turns every feature into a negotiation\nacross three teams.\n\nThe reliable test: if a routine change requires coordinated deployment across two components, the\nboundary is wrong regardless of how clean the diagram looks.\n\nPrefer coarse boundaries until you have evidence for finer ones. Distributed systems convert simple\nin-process failures into network, partial-failure and consistency problems — a cost worth paying for\nindependent scaling or independent deployment, and not worth paying for tidiness.\n\n## Trade-offs, stated\n\nEvery architecture sacrifices something. The failure is not choosing badly; it is choosing without\nnaming what was given up, so nobody later understands why the constraint exists.\n\nPresent options with their costs: what each makes easy, what each makes hard, what it costs to\noperate, and what it would take to reverse. Two credible options and an honest comparison beat one\nrecommendation.\n\n## Record decisions\n\nWrite down the decision, the context at the time, the options considered, and the consequences\naccepted. Architecture rots because the reasoning evaporates while the structure remains, and the\nnext team reads a constraint as an accident.\n\nKeep records short and immutable — supersede rather than edit, so the history of thinking survives.\n\n## Sources\n\n`references/sources.md` in this skill lists the outside authorities that settle the questions\nhere — what each one is authoritative for, and what you may do with it. Check them before\nanswering on anything they cover, and cite what you used. Most are free to read and not free\nto reproduce; the use note on each is binding.\n\n## Never\n\n- Design against quality attributes nobody has quantified.\n- Split a system into services to make the diagram tidy.\n- Present a single option as though no trade-off was made.\n- Leave an expensive-to-reverse decision undocumented.\n"
}