[Raiden Weight Sync 5/7] Pass weight_dtype in Qwen3NextSparseMoeBlock shared expert gate

[YixuanWang-99]

Overview

Part of the stacked Raiden weight-sync enablement PR chain replacing #5089.

Stack:

• [M7] [Raiden Weight Sync 1/7] Add cross-repo drift guard and FFI resolution tests #5166: Cross-repo drift guard
• [M1] [Raiden Weight Sync 2/7] Support inhomogeneous layer cycle interval in raiden_unscan #5167: Inhomogeneous layer cycle support in raiden_unscan
• [M2] [Raiden Weight Sync 3/7] MoE 128-lane layout and padding for TPU GMM kernels #5168: MoE 128-lane layout and padding (pairs with Tunix T5)
• [M3] [Raiden Weight Sync 4/7] Target-free and streaming weight conversion for vLLM #5169: Target-free streaming weight conversion
• [M5] AI-Hypercomputer/maxtext (this PR): Shared expert gate weight_dtype fix
• [M4] AI-Hypercomputer/maxtext: TrainingEngine Raiden FFI integration (pairs with Tunix T2a)
• [M6] AI-Hypercomputer/maxtext: Rollout cleanup

Details

• Fixes shared_expert_gate in Qwen3NextSparseMoeBlock to explicitly pass weight_dtype=cfg.weight_dtype.

Checklist

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[gemini-code-assist]

Code Review

This pull request updates the Qwen3 model implementation in src/maxtext/models/qwen3.py to explicitly set the weight_dtype parameter to cfg.weight_dtype during the initialization of the shared expert gate. There are no review comments, and I have no additional feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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