Generate typed nested resource dataclasses

[razor-x]

Motivation

• Nested resource properties were emitted as untyped mappings (Dict[str, Any] or DeepAttrDict) which conflicted with runtime hydration and prevented attribute completion and nested docs.
• Arrays of object-shaped items (e.g. errors/warnings) were left as lists of bare dicts, forcing subscript access and losing attribute access.
• Generated docstrings only documented top-level fields and nested unknown keys were not stripped, making the SDK less safe and discoverable.
• The project lacked a PEP 561 marker and a typing gate, so these regressions were not enforced by CI.

Description

• Make the code generator recursively discover and register nested object classes and discriminated-object variants in codegen/lib/layouts/resources.ts, producing nested class contexts and per-property metadata.
• Update type mapping to return generated nested class names in codegen/lib/python-type.ts and change templates (codegen/layouts/resource.hbs and codegen/layouts/partials/resource-dataclass.hbs) to emit nested dataclasses before the parent and to hydrate objects and lists of objects using from_dict.
• Add a small mapping-compat shim seam/utils/resource_mapping.py that nested dataclasses inherit so they remain indexable and support .get(), in, iteration, and .keys() while becoming real typed dataclasses; leave record properties as Dict[str, Any].
• Ship PEP 561 marker seam/py.typed, add mypy to dev dependencies and just lint, regenerate the seam/resources/ modules (many files updated), and add regression tests in test/nested_resource_test.py covering nested hydration, list-of-object hydration, unknown key stripping, record passthrough, mapping compatibility, and union hydration for action_attempt.

Testing

• Ran generation and static checks: npx tsx codegen/smith.ts, npm run lint, and npm run typecheck which completed successfully.
• Ran Python formatting and static typing: python -m black --check ., python -m mypy seam/resources --disable-error-code=arg-type --disable-error-code=import-not-found, and python -m compileall -q seam, which succeeded for the modified resources.
• Executed the new unit tests via python -m pytest test/nested_resource_test.py, which failed to run end-to-end due to a missing runtime dependency (urllib3) in the execution environment (test harness), not due to the generated code itself.
• Confirmed generated changes: Device.properties is now typed as DeviceProperties, errors/warnings are typed lists of nested dataclasses, custom_metadata remains Dict[str, Any], and nested classes are documented and hydrated in from_dict.

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Codex Task