Fix duplicate predefined tools in dynamic tools system message

[MumuTW]

Summary

• iterate only over tools without predefined system-message descriptions when building the dynamic tool definitions section
• prevent built-in/predefined tools from being duplicated when MCP/dynamic tools are present
• add a regression assertion verifying predefined tools appear only once in mixed tool lists

Fixes #11064.

Testing

• Unable to run local vitest in this workspace because project dependencies are not installed (node_modules missing).

---

Summary by cubic

Prevents duplicate predefined tools in the dynamic tools section of the system message. Only tools without a predefined description are included, and a test guards against regressions.

• Bug Fixes
  • Generate dynamic definitions from tools with dynamic messages only.
  • Avoid duplicating built-in/predefined tools when dynamic tools are present.
  • Add regression assertion to ensure predefined tools appear once in mixed lists.

^{Written for commit 8a16aa7. Summary will update on new commits.}

[MumuTW]

I have read the CLA Document and I hereby sign the CLA

[cubic-dev-ai]

No issues found across 2 files

[RomneyDa]

@MumuTW nice find!

[RomneyDa]

Credit to @shanevcantwell for also finding and fixing this bug on #11068