fix(tool): guard Object.entries against null in ToolRegistry.state

[SpencerJung]

Fixes #27456. Adds null/undefined guards before Object.entries() calls in ToolRegistry.state to prevent crashes when tool modules contain re-exports or unexpected shapes.

[ghost]

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[ghost]

The following comment was made by an LLM, it may be inaccurate:

Found a potential duplicate:

PR #27512: "fix: add null checks in ToolRegistry to handle re-export barrels"
#27512

This appears to be closely related to PR #29369. Both PRs address adding null checks in ToolRegistry to handle edge cases with re-exports and prevent crashes when tool modules have unexpected shapes. The #27512 PR specifically mentions "re-export barrels" which aligns with the description of the current PR.

You may want to verify if #27512 was already merged and if this PR (#29369) is addressing the same issue or a different occurrence.