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.NET: Preserve harness middleware for dynamic tools - #8402

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Roger Barreto (rogerbarreto) merged 7 commits into
microsoft:mainfrom
rogerbarreto:rogerbarreto/function-middleware-harness
Sep 18, 2026
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.NET: Preserve harness middleware for dynamic tools#8402
Roger Barreto (rogerbarreto) merged 7 commits into
microsoft:mainfrom
rogerbarreto:rogerbarreto/function-middleware-harness

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@rogerbarreto

@rogerbarreto Roger Barreto (rogerbarreto) commented Sep 15, 2026

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Motivation & Context

Keep harness function middleware consistent when an agent's tool collection evolves during a run. This proposal preserves middleware composition for dynamic tools while retaining the existing function-calling pipeline and reusable run-options configuration.

Description & Review Guide

  • What are the major changes? Add a private, per-request FunctionMiddlewarePreservingChatClient and a middleware-aware tool collection. Preserve callback composition across tool additions, replacements, and option cloning without adding agent state to the options types. Extend .NET regression coverage and add Python regression-only coverage for its existing behavior.
  • What is the impact of these changes? Dynamic tools retain the registered callbacks without changing public APIs or dependencies. The existing function wrappers and FunctionInvokingChatClient remain responsible for their current roles; caller-owned options and shared clients are not modified.
  • What do you want reviewers to focus on? Compatibility of callback ordering and continuation behavior, collection replacement, approval handling, custom clients, and isolation when options or clients are reused across runs.

Related Issue

No public issue linked.

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 AI balanced review requested due to automatic review settings September 15, 2026 15:54
@agent-framework-automation agent-framework-automation Bot added python Usage: [Issues, PRs], Target: Python .NET Usage: [Issues, PRs], Target: .Net labels Sep 15, 2026
@github-actions github-actions Bot changed the title .NET: Preserve harness middleware for dynamic tools Python: .NET: Preserve harness middleware for dynamic tools Sep 15, 2026
Copilot AI reviewed Sep 15, 2026

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Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

github-actions[bot]
github-actions Bot reviewed Sep 15, 2026
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MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): ef0182a95c90
Model: gpt-5.6-sol-fast

Overview

The change keeps function middleware request-scoped by cloning run and chat options, wraps collection mutations, and reapplies wrapping after whole-collection replacement; the added tests cover ordering, approval metadata, streaming parity, and shared-client isolation. One composition gap remains: middleware-chain discovery depends on every custom chat-client decorator forwarding GetService, so a supported opaque decorator can cause later replacement tools to lose callbacks.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
1 verified finding remained after source verification (1 medium) across 1 file. Details are attached to the affected lines below.

Affected areas: dotnet/src/Microsoft.Agents.AI/FunctionInvocationDelegatingAgent.cs

Comment thread dotnet/src/Microsoft.Agents.AI/FunctionInvocationDelegatingAgent.cs Outdated
@rogerbarreto
fix: preserve dynamic function middleware
af61570 
Keep harness callbacks consistent as tool collections change.
Preserve existing function wrappers and request-local composition
without coupling reusable options to agent instances.
@rogerbarreto
fix: compose harness middleware across clients
d9eb7fd 
Keep callback composition independent of client service discovery.
Use request-local execution scopes without changing reusable options.
Cover scope restoration and tool repair after collection updates.
@rogerbarreto
Roger Barreto (rogerbarreto) force-pushed the rogerbarreto/function-middleware-harness branch from ef0182a to d9eb7fd Compare September 15, 2026 18:16
@rogerbarreto Roger Barreto (rogerbarreto) changed the title Python: .NET: Preserve harness middleware for dynamic tools .NET: Preserve harness middleware for dynamic tools Sep 15, 2026
@rogerbarreto
fix: retain middleware through options clones
20087cc 
Keep harness callback composition consistent across function-loop
iterations by retaining the full chain on function wrappers.
Cover real client-driven clones, repeated calls and approval flows.
eavanvalkenburg
Eduard van Valkenburg (eavanvalkenburg) approved these changes Sep 16, 2026
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@eavanvalkenburg Eduard van Valkenburg (eavanvalkenburg) left a comment

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Small nit on the code.

Comment thread python/packages/core/tests/core/test_function_invocation_logic.py Outdated
@rogerbarreto
test: extend dynamic tool middleware coverage
33dd41e 
Cover Python harness callback consistency across progressive tool
loading, continuation changes, failures, approvals and reused options.
@rogerbarreto
Roger Barreto (rogerbarreto) marked this pull request as ready for review September 16, 2026 11:03
westey-m
westey (westey-m) reviewed Sep 16, 2026
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Comment thread dotnet/src/Microsoft.Agents.AI/FunctionInvocationDelegatingAgent.cs
@rogerbarreto
docs(dotnet): explain function callback flow
f46c017 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@rogerbarreto
Roger Barreto (rogerbarreto) added this pull request to the merge queue Sep 18, 2026
Merged via the queue into microsoft:main with commit f2ba504 Sep 18, 2026
47 checks passed
@rogerbarreto
Roger Barreto (rogerbarreto) deleted the rogerbarreto/function-middleware-harness branch September 18, 2026 14:50
This was referenced Sep 18, 2026
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@eavanvalkenburg Eduard van Valkenburg (eavanvalkenburg) eavanvalkenburg approved these changes
@westey-m westey (westey-m) westey-m approved these changes
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@rogerbarreto Roger Barreto (rogerbarreto)

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