Python: Fix duplicate streamed tool calls in DevUI

[Chinedum Echeta (cecheta)]

Motivation & Context

DevUI renders repeated copies of a single streamed tool call when the provider includes the same call ID and function name on each arguments chunk. This makes one framework tool execution appear as several calls in the chat.

The mapper should announce each unique function call once and continue forwarding all argument deltas for that call.

Description & Review Guide

• What are the major changes? MessageMapper now emits response.output_item.added only when a function call ID is first observed. A regression test covers two argument chunks that repeat the same call metadata.
• What is the impact of these changes? DevUI displays one tool-call item per framework call while preserving streamed arguments. There is no public API change.
• What do you want reviewers to focus on? Confirm that using the request-scoped active_function_calls map correctly handles repeated provider metadata without affecting parallel calls.

Related Issue

Fixes #7651

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Fixes duplicate DevUI tool-call items while preserving streamed argument deltas.

Changes:

• Emits tool-call creation events only for unseen call IDs.
• Adds regression coverage for repeated streamed metadata.

Show a summary per file

File	Description
python/packages/devui/agent_framework_devui/_mapper.py	Deduplicates streamed tool-call items by call ID.
python/packages/devui/tests/devui/test_mapper.py	Tests single-item emission and complete argument streaming.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	45879	4239	90%

report-only-changed-files is enabled. No files were changed during this commit :)

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
9346	36 💤	0 ❌	0 🔥	2m 32s ⏱️