Add routeCheckout (messy demo — should be caught)

[JordanCoin]

🤖 crap4swift review — the "caught" showcase

This PR adds routeCheckout(_:_:), deliberately messy: high complexity, no tests, and
several SwiftLint violations. crap4swift, scoped to just this diff, flags all of it:

CRAP	CC	Coverage	Function	Lint
132 ⚠️	11	0%	routeCheckout(…)	force_cast + 2× identifier_name

Verdict: request-changes. CRAP 132 (≫ threshold 30) — 11 branches, zero coverage.
Plus a force_cast (line 6) and short identifiers p/q. This is exactly the kind of
change a reviewer should stop: complex, untested, and unsafe. The CI check fails by
design — the gate caught it.

The auto-posted comment below carries the full risk map (CRAP + SwiftLint) for the
review agent to reason about. Compare with #1, where the same shape of function passed
once it was tested.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[github-actions]

crap4swift — changed-function risk

{
  "base" : "3b45ed2e208ea4e298f04c628c562d2125f2293f",
  "functions" : [
    {
      "complexity" : 11,
      "coverage" : 0,
      "crap" : 132,
      "endLine" : 18,
      "file" : "/__w/crap4swift/crap4swift/Sources/CrapCore/Checkout.swift",
      "function" : "routeCheckout(…)",
      "lint" : [
        {
          "line" : 6,
          "reason" : "Force casts should be avoided",
          "rule" : "force_cast",
          "severity" : "Error"
        },
        {
          "line" : 6,
          "reason" : "Variable name 'p' should be between 3 and 40 characters long",
          "rule" : "identifier_name",
          "severity" : "Error"
        },
        {
          "line" : 15,
          "reason" : "Variable name 'q' should be between 3 and 40 characters long",
          "rule" : "identifier_name",
          "severity" : "Error"
        }
      ],
      "overThreshold" : true,
      "startLine" : 5
    }
  ],
  "summary" : {
    "count" : 1,
    "overThreshold" : 1,
    "worst" : "routeCheckout(…)"
  },
  "threshold" : 30
}

[JordanCoin]

Closing — this was a deliberate demo of crap4swift catching untested, high-CRAP, lint-flagged code (red by design). It served its purpose; the auto-posted risk-map comment stays visible here as an example. Not for merge.