Python: Add Foundry Hosted Agent history provider

[eavanvalkenburg]

Motivation & Context

Adds the smallest Foundry Hosted Agent history-provider slice needed by the broader hosting/channel work. On its own this is not especially useful: it becomes meaningful together with the new agent-framework-hosting packages, where it provides the persistence piece for building Foundry Hosted Agents using the new host/channel model.

This gives apps an alternative path to the existing ResponsesHostServer setup: use the new hosting packages for route/channel composition, while this provider handles Foundry-compatible response history. This PR intentionally avoids the broader Foundry hosting rewrites from the original feature branch. See ADR-0027 and ADR-0028 for the purpose, intended use, and follow-up boundaries of the hosting work.

Description & Review Guide

• What are the major changes?
  • Adds FoundryHostedAgentHistoryProvider in agent_framework_foundry_hosting.
  • Adds Foundry-compatible foundry_response_id helpers used by the provider/channel response-id flow.
  • Marks the hosting provider APIs as experimental under ExperimentalFeature.HOSTING.
  • Adds provider tests for local round-trip persistence, chained response history, hosted credential validation, experimental metadata, and ID shape.
• What is the impact of these changes?
  • Later hosted-agent samples can use a Foundry-compatible history provider with the new host/channel packages.
  • Existing ResponsesHostServer and InvocationsHostServer behavior is unchanged.
• What do you want reviewers to focus on?
  • Correctness of the code in this slice. The broader purpose and intended use are covered by the hosting ADRs.

Related Issue

Fixes #6586
Refs #6265

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

This PR introduces a minimal public helper in the agent_framework_foundry_hosting Python package to mint Foundry-hosted-agent-compatible response IDs, so upcoming hosting/channel samples can generate accepted IDs without reaching into Azure SDK implementation details at call sites.

Changes:

• Added a new agent_framework_foundry_hosting.hosted_agents helper module providing foundry_response_id() and foundry_response_id_factory().
• Added unit tests validating response ID shape, partition-key reuse across chained responses, and the factory hook behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/packages/foundry_hosting/agent_framework_foundry_hosting/hosted_agents.py	Adds the Foundry response ID helper functions and factory type alias.
python/packages/foundry_hosting/tests/foundry_hosting/test_hosted_agents.py	Adds focused tests for ID shape, partition key reuse, and factory behavior.

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_feature_stage.py	169	10	94%	110, 156, 211, 222, 242, 280, 291, 297, 328, 356
packages/foundry_hosting/agent_framework_foundry_hosting
_history_provider.py	125	24	80%	76, 90–98, 211–212, 215, 225–230, 244, 250, 266, 305, 308
TOTAL	39976	4521	88%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
7993	34 💤	0 ❌	0 🔥	2m 9s ⏱️

[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 83% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by eavanvalkenburg's agents