Diagnose and fix pip ResolutionImpossible errors and slow dependency-resolution backtracking

Documented steps

1. Read the ResolutionImpossible error block: pip lists which of your requirements (or their dependencies) demand incompatible versions of the same package — e.g. one needs pkg<3.0 while another needs pkg==2.3.1.
2. First upgrade pip itself (pip install --upgrade pip) so you're on the current backtracking resolver and its latest improvements.
3. If the conflict is between YOUR pins, loosen one: widen the version range of the less critical requirement so an overlapping version exists.
4. If resolution is merely slow (pip keeps downloading many versions of the same package), that is backtracking at work, not a bug — either wait, or pin the package that pip is churning on to a known-good version to cut the search space.
5. Use a constraints file for indirect dependencies: put pins like problem-pkg==2.4.2 in constraints.txt and install with pip install -c constraints.txt -r requirements.txt — constraints steer the resolver without adding new requirements.
6. Install packages that must coexist in ONE pip invocation; sequential single-package installs resolve independently and can produce mutually broken environments.
7. Preview what would be installed without changing the env: pip install --dry-run (optionally --report <file.json> for a full resolution report).
8. If no version combination can satisfy everything, the conflict is real: swap one dependency for an alternative, vendor/isolate, or split components into separate environments. Docs: https://pip.pypa.io/en/stable/topics/dependency-resolution/