fix(types): resolve capability sub-models via field annotation, not numbered names

[bokelley]

Summary

• Restores Validate schemas are up-to-date on main (failing since 49c4b5ab, May 14).
• Roots out the cause: capabilities.py was importing Features2 as SignalsFeatures and Idempotency3 as IdempotencyUnsupported — both are codegen-internal numbered names that drift across regens.
• Resolves them via parent field annotation (Signals.features / Adcp.idempotency) instead, so the imports survive future renumbering.

Root cause

datamodel-code-generator 0.56.1 numbers inline-schema classes from a global counter whose traversal order depends on filesystem iteration. Reproduced in a Linux 3.11-slim Docker container against schemas 3.0.7:

• macOS regen → Features + Features2, Idempotency + Idempotency3
• Linux regen → Features + Features1, Idempotency + Idempotency1

The committed bundled file was generated when the counter produced Features2/Idempotency3. Today's regen (same pinned generator) produces Features1/Idempotency1, so capabilities.py:117 blows up with ImportError: cannot import name 'Features2' during the Generate models step, taking the whole adcp package import down with it.

The fix

Reach the classes via the parent's field annotation — Signals and Adcp are stable wire-spec class names; the union arm types live directly on the field annotations:

_signals_features_arms = [
    arm for arm in _get_args(_Signals.model_fields["features"].annotation)
    if arm is not type(None)
]
SignalsFeatures: type = _signals_features_arms[0]

_idempotency_arms = [
    arm for arm in _get_args(_Adcp.model_fields["idempotency"].annotation)
    if arm is not IdempotencySupported and arm is not type(None)
]
IdempotencyUnsupported: type = _idempotency_arms[0]

Both lookups raise loudly if the annotation shape ever changes — silent mis-resolution beats import-time bombs, but a clear RuntimeError at boot beats both.

Also in this PR (regen drift)

The same python scripts/generate_types.py produced minor cosmetic drift the previous regen never committed:

• SCHEMA_DELTAS.md — previously reported extension_meta delta is already merged upstream.
• _ergonomic.py — list[...] → Sequence[...] in three BeforeValidator annotations.
• enum + media_buy bundled files — duplicate-import cleanup.

Test plan

• pytest tests/ -x → 4731 passed, 34 skipped, 1 xfailed
• mypy src/adcp/types/capabilities.py src/adcp/decisioning/capabilities.py → clean
• ruff check src/adcp/types/capabilities.py → clean
• Reproduced the CI failure in Linux Docker; verified the fix resolves SignalsFeatures → Features1 and IdempotencyUnsupported → Idempotency1 cleanly after fresh regen.

🤖 Generated with Claude Code