fix(vcs-core): reuse resolved driver schema during exec

[mturac]

Summary

• reuse the resolved driver schema during VcsCore.exec dispatch validation
• preserve the existing driver.describe() fallback for callers that do not pass a cached schema
• enable the issue VcsCore.exec re-resolves the binding contract on every exec under the always-on carrier (caching regression since #4) #11 regression test by removing the xfail marker

Fixes #11.

Validation

• uv run pytest vcs-core/packages/core/tests/unit/test_binding_surface.py::test_vcscore_exec_uses_cached_resolved_binding_contract_without_runtime_describe -q
• uv run pytest vcs-core/packages/core/tests/unit/test_binding_surface.py -q
• uv run pytest vcs-core/packages/core/tests/unit/test_base_substrate_driver.py vcs-core/packages/core/tests/integration/vcscore/test_commands.py -q
• uv run ruff check vcs-core/packages/core/src/vcs_core/_substrate_driver.py vcs-core/packages/core/src/vcs_core/_vcscore_runtime.py vcs-core/packages/core/src/vcs_core/_world_transition_coordinator.py vcs-core/packages/core/tests/unit/test_binding_surface.py
• uv run --package vcs-core --group typing mypy vcs-core/packages/core/src/vcs_core/_substrate_driver.py vcs-core/packages/core/src/vcs_core/_vcscore_runtime.py vcs-core/packages/core/src/vcs_core/_world_transition_coordinator.py

[dcx]

Hello, thank you for your contribution! I'll try to review this later today.

[mturac]

Validation refreshed on the current head:

git diff --check origin/main...HEAD
uv run pytest vcs-core/packages/core/tests/unit/test_binding_surface.py::test_vcscore_exec_uses_cached_resolved_binding_contract_without_runtime_describe -q
uv run pytest vcs-core/packages/core/tests/unit/test_binding_surface.py -q
uv run pytest vcs-core/packages/core/tests/unit/test_base_substrate_driver.py vcs-core/packages/core/tests/integration/vcscore/test_commands.py -q
uv run ruff check vcs-core/packages/core/src/vcs_core/_substrate_driver.py vcs-core/packages/core/src/vcs_core/_vcscore_runtime.py vcs-core/packages/core/src/vcs_core/_world_transition_coordinator.py vcs-core/packages/core/tests/unit/test_binding_surface.py
uv run --package vcs-core --group typing mypy vcs-core/packages/core/src/vcs_core/_substrate_driver.py vcs-core/packages/core/src/vcs_core/_vcscore_runtime.py vcs-core/packages/core/src/vcs_core/_world_transition_coordinator.py

All passed locally. The current ruff/gates/macOS test checks are also green on this head.

[mturac]

Rebased this branch onto the current main and revalidated the new head 3935c6d0fe3624d6d55a0ae1da5bfb9fc34fa9c7.

git diff --check origin/main...HEAD
cd vcs-core/packages/core && uv run --group test pytest tests/unit/test_binding_surface.py -q
cd vcs-core/packages/core && uv run --group lint ruff check src/vcs_core/_substrate_driver.py src/vcs_core/_vcscore_runtime.py src/vcs_core/_world_transition_coordinator.py tests/unit/test_binding_surface.py
cd vcs-core/packages/core && uv run --group lint ruff format src/vcs_core/_substrate_driver.py src/vcs_core/_vcscore_runtime.py src/vcs_core/_world_transition_coordinator.py tests/unit/test_binding_surface.py --diff
cd vcs-core/packages/core && uv run --group typing mypy src/vcs_core/_substrate_driver.py src/vcs_core/_vcscore_runtime.py src/vcs_core/_world_transition_coordinator.py
make -C vcs-core/packages/core test PYTEST_XDIST= TEST_FILE=tests/unit/test_binding_surface.py

All pass locally.