[SDK] Add Changes to Clone Downstream and Upstream Header Contexts

[SavinduDimal]

Purpose

• $Subject
• Related Issues: [Bug]: Set Header policy takes effect before mcp_auth policy #2548

Description

This pull request introduces support for immutable snapshots of original client request and upstream response headers in both the Go and Python SDKs. These snapshots, represented by new DownstreamContext and UpstreamContext types, are now available in all policy context objects, allowing policies to access unchanged headers.

New Context Types and Header Snapshots:

• Added DownstreamContext and UpstreamContext types to both Go (context.go) and Python (types.py) SDKs, each holding immutable copies of original client request and upstream response headers, respectively. [1] [2]
• Updated all request, response, and streaming context structs/classes (e.g., RequestHeaderContext, ResponseHeaderContext, RequestStreamContext, etc.) to include optional downstream and upstream fields referencing these new context types. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Python SDK Integration:

• Registered DownstreamContext and UpstreamContext in the Python SDK’s __init__.py and __all__ to ensure they are exported and available for import. [1] [2] [3]

Backward Compatibility:

• Documented that these fields may be None (Python) or nil (Go) on older gateways, and policies should fall back to legacy header validation if unavailable. [1] [2]

These changes improve policy reliability by allowing access to original, unmodified headers, while maintaining backward compatibility with older gateway versions.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 9a14fc41-22f5-48af-8b01-e3c5fd4e2f71

📥 Commits

Reviewing files that changed from the base of the PR and between 1f365f7 and cab5934.

📒 Files selected for processing (2)

• sdk-python/src/apip_sdk_core/policy/v1alpha2/__init__.py
• sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py

📝 Walkthrough

Walkthrough

The policy SDK context APIs now define downstream and upstream header snapshot types and expose them through request, response, and streaming context dataclasses and structs in Python and Go.

Changes

Gateway header context snapshots

Layer / File(s)	Summary
Snapshot types and public exports sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py, sdk/core/policy/v1alpha2/context.go, sdk-python/src/apip_sdk_core/policy/v1alpha2/__init__.py	Adds immutable DownstreamContext and UpstreamContext types containing header snapshots and exports them from the Python module.
Request context propagation sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py, sdk/core/policy/v1alpha2/context.go	Adds optional downstream context fields to request header, request, and streaming request contexts.
Response context propagation sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py, sdk/core/policy/v1alpha2/context.go	Adds optional downstream and upstream context fields to response header, response, and streaming response contexts.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: anugayan, arshardh, ashera96, malinthaprasan, tharsanan1

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers purpose and high-level changes, but it omits most required template sections like goals, approach, tests, security, and environment.	Add the missing template sections: Goals, Approach, User stories, Documentation, Automation tests, Security checks, Samples, Related PRs, and Test environment.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the main change by describing new downstream and upstream header context cloning in the SDKs.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py`:
- Around line 132-153: Make the headers fields in DownstreamContext and
UpstreamContext nullable to match the documented unavailable-state behavior and
the Go SDK contract. Update both annotations and defaults so instances can
represent None rather than always constructing Headers(), while preserving the
existing context classes and docstrings.

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Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 8e28d677-516c-4bc1-822e-7da2b72469d3

📥 Commits

Reviewing files that changed from the base of the PR and between 61ed191 and 1f365f7.

📒 Files selected for processing (3)

• sdk-python/src/apip_sdk_core/policy/v1alpha2/__init__.py
• sdk-python/src/apip_sdk_core/policy/v1alpha2/types.py
• sdk/core/policy/v1alpha2/context.go