[WH-2099]

Important

Read the contribution guidelines and checked related issues and pull requests.

Related Issue

Closes #375

Summary

Streaming LLM completion callbacks currently omit tool calls, and exceptions raised while reading the stream skip the error callback.
Include assembled tool calls in on_after_invoke using the existing delta merger, and notify on_invoke_error with the original exception before propagating stream failures.
Invocation, token counting, and callback signatures consistently accept Sequence[PromptMessage], matching their read-only use of the input collection.

Regression coverage exercises complete calls, interleaved argument fragments, and failures before or after the first chunk, with blocking calls as controls.
Existing scenarios also use tuple prompts: four argument-type errors reproduce the restrictive signatures, and the updated signatures pass the full type check.

Validation:

• just check: passed, including full type checking.
• Model dispatch tests: 55 passed.
• just test: 1067 passed.

Checklist

• This pull request links the issue it resolves or advances
• This pull request title follows Conventional Commits, and any breaking change is marked with !
• If CLA Assistant prompted me, I signed CLA.md in the pull request conversation

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has insufficient remaining quota.

An organization owner can choose the repository organization as the billing source for reviews requested by members with a paid Copilot license. Learn about Copilot code review billing. Review the Copilot code review billing settings.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has insufficient remaining quota.

An organization owner can choose the repository organization as the billing source for reviews requested by members with a paid Copilot license. Learn about Copilot code review billing. Review the Copilot code review billing settings.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has insufficient remaining quota.

An organization owner can choose the repository organization as the billing source for reviews requested by members with a paid Copilot license. Learn about Copilot code review billing. Review the Copilot code review billing settings.