JSON Pointer (RFC 6901)

You are completing a coding task in one shot. Write complete files that satisfy the spec below. Tests (pytest) will be run against your files; you cannot run them yourself.

Reply with ONE JSON object and nothing else:
{"files": {"<relative path>": "<complete file content>", ...}}

Required deliverable files: jsonpointer.py

SPEC:
Create jsonpointer.py with exactly one function:

resolve(doc, pointer: str)
    Resolve an RFC 6901 JSON Pointer against doc (nested dicts/lists) and return the referenced value.

Rules:
- The empty pointer "" refers to the whole document.
- A pointer is a sequence of /-prefixed reference tokens: "/a/b" means doc["a"]["b"].
- In a token, the escape ~1 decodes to "/" and ~0 decodes to "~" (decode ~1 before ~0).
- Tokens indexing a list are decimal indices: "/items/0" is the first element.
- Raise KeyError for anything that does not resolve (missing key, bad or out-of-range index, pointer not starting with "/", descending into a scalar).

Use only the Python standard library.

{"files": {"jsonpointer.py": """"import json

def resolve(doc, pointer: str):
    if not pointer:
        return doc
    parts = pointer.split('/')
    current = doc
    for part in parts:
        if part.startswith('~'):
            part = part[1:]
            if part == '0':
                continue
            elif part == '1':
                part = '/'
            else:
                raise KeyError(f"Invalid escape sequence in pointer: {pointer}")
        if not isinstance(current, dict) and not current:
            raise KeyError(pointer)
        if part.isdigit():
            index = int(part)
            if not isinstance(current, list) or index < 0 or index >= len(current):
                raise KeyError(pointer)
            current = current[index]
        else:
            current = current.get(part)
    return current"}}