Seed <repeat default=N> only when a request omits the repeat

[guerler]

Follow up for: #23084, focussing on repeat seeding.

This change ensures repeat parameters consistently honor their declared default value during tool request execution. If a repeat is omitted from the request, the default number of instances is created, if an explicit empty list is provided, zero instances are preserved, and min continues to enforce the minimum number of instances. The default value is clamped to the configured [min, max] range during parsing, matching the parameter model. This prevents tools that rely on default repeat values from receiving malformed inputs while preserving the semantics of structured tool requests.

How to test the changes?

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• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

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