[stobrien89]

Issue #, if available:
#797

Description

Partitions large standalone types packages to reduce generation memory and static analysis time.

Stacked on #866 and intended to be reviewed against native-types-cli-integration.

Changes

• Partition schemas above 250 shapes using weighted source-size boundaries.
• Keep recursive schema components in the same partition.
• Partition model stubs above 250 declarations.
• Preserve stable schemas.py and models.pyi facades.
• Preserve single-file output for packages at or below each threshold.

EC2 benchmark

Measured on x86 with 4,065 selected shapes, five runs, and one warmup.

Metric	Unpartitioned	Partitioned	Change
Generation time	3.557 s	3.555 s	-0.1%
Peak RSS	264.5 MiB	122.4 MiB	-53.7%
Peak Python allocation	222.6 MiB	84.7 MiB	-61.9%
Generated bytes	4.78 MiB	5.33 MiB	+11.6%
Model import	50.6 ms	40.4 ms	-20.2%
First model access	12.3 ms	22.3 ms	+10.0 ms
Strict Pyright	81.98 s	15.25 s	-81.4%

Validation

• Tests cover schema and stub output below, at, and above the 250-item threshold.
• Tests verify recursive component placement, cross-partition references, facade caching, deterministic output, and stable public exports.
• Partitioned generated packages pass Ruff and strict Pyright.

Compatibility

Public model imports, lazy model construction, schema identity, serde behavior, and typing remain unchanged. Partition files live under _private.

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[Copilot]

🟡 Changes recommended

Generated-output compatibility and lint failures remain, alongside schema-planning and partition-weighting issues that undermine scalability.

4 open issues

• Re-export unused private deserializer helpers · New
• Add planned schema constants to lazy facade all · New
• Avoid quadratic recursive component ordering · New
• Include interned string declarations in partition weight estimates · New

What changed in this PR

This PR extends the native standalone types generator with private schema and model-stub partitions, reducing memory use and static analysis time while retaining stable facade modules.

Changes:

• Adds configurable partition targets, defaulting to 250 items.
• Balances schema partitions by estimated source size and keeps recursive components together.
• Adds partitioning tests and documents output layout, compatibility, and benchmark results.

File	Description
packages/​smithy-python/​tests/​unit/​test_schemas.py	Tests thresholds, lazy loading, recursion, and size balancing.
packages/​smithy-python/​tests/​unit/​test_models.py	Tests partitioned stubs, public models, and strict Pyright.
packages/​smithy-python/​tests/​unit/​test_generation.py	Tests partition defaults and positive-value validation.
packages/​smithy-python/​src/​smithy_python/​schemas.py	Adds weighted schema partitions and a lazy facade.
packages/​smithy-python/​src/​smithy_python/​models.py	Adds private stub partitions and public re-exports.
packages/​smithy-python/​src/​smithy_python/​generation.py	Defines and validates partition settings.
designs/​codegen/​types.md	Updates settings and large-model design guidance.
designs/​codegen/​partitioning.md	Documents partitioning behavior and performance measurements.
designs/​codegen/​index.md	Links the partitioning design.

_{Review effort: Balanced}

[Copilot]

🟢 Approval recommended

Static review found no blocking issues in partitioning, facade behavior, or compatibility, and the supporting tests cover the key boundaries.

No open issues 🎉

4 resolved since last review

• Include interned string declarations in partition weight estimates
• Avoid quadratic recursive component ordering
• Add planned schema constants to lazy facade all
• Re-export unused private deserializer helpers

_{Review effort: Balanced}