Cross-Language Type Traps

Opening Scenario

You're building a data pipeline. A Python service produces JSON; a Java service consumes it; a C++ service computes numerics for both. Tests pass in isolation. In production, three bugs land the same week:

1. A user ID 9007199254740993 from the Python service arrives as 9007199254740992 in a JavaScript dashboard.
2. A C++ function receives count = -1 from Java, then reads past the end of an array.
3. A Python server compares a JSON field with if value: and treats the string "0" as truthy. Later, a Java call site uses "0".equals(value) on the same field and agrees. Everyone disagrees about what "empty" means.

None of these are "bugs" in any one language. They are bugs at the seams — the places where types cross a boundary. You can't avoid cross-language work; you can only learn where the trapdoors are.

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Question Progression

Q1: Why do integers stop meaning the same thing across languages?

Question: Python integers are arbitrarily large. Java's…