bug: CI installs a Python 3.14-incompatible LiteLLM release

[rlippmann]

Description

• On Friday, July 17, 2026, PR feat: add public directive grammar foundation #189 failed in the test (3.14) CI job while installing the demo-only litellm dependency.
• The failure is not caused by Context Compiler logic. It happens because the workflow installs unpinned litellm, which currently resolves to a release path that is not ready for Python 3.14.
• The immediate workaround in PR feat: add public directive grammar foundation #189 is to set PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 on that install step.
• We should decide whether the longer-term fix should be:
  • keeping the env-var workaround,
  • pinning CI to a known-good LiteLLM version,
  • narrowing the demo dependency range, or
  • changing how the 3.14 job exercises optional demo dependencies.

Reproduction

• Open PR feat: add public directive grammar foundation #189 or run the current CI workflow on branch grammar-boundary.
• Inspect the test (3.14) job from GitHub Actions run 29555668230.
• The failing step is Install mypy demo dependencies.
• The logged failure shows PyO3 rejecting Python 3.14 while building/installing LiteLLM:
  • configured Python interpreter version: 3.14
  • PyO3 maximum supported version: 3.13

Expected behavior

• The CI matrix should complete successfully on Python 3.14 without depending on an unpinned optional demo dependency path that is not yet 3.14-compatible.