Merge User-Agent headers when cloning HTTP client

[Copilot]

When Client.clone() was called with headers containing a User-Agent, it would overwrite the base client's User-Agent rather than merging. This loses the SDK's default UA token when callers supply their own.

Changes

• packages/common/src/microsoft_teams/common/http/client.py

  • Added _merge_headers(base, overrides) helper: performs a case-insensitive User-Agent merge (space-concatenated, token-based dedup to avoid substring false positives); all other headers follow standard last-write-wins semantics
  • Client.clone() now calls _merge_headers() instead of a plain dict unpack

• packages/common/tests/test_client.py

  • Added 7 tests covering: preservation without overrides, merge when both sides define UA, non-UA overrides leave UA untouched, case-insensitive key matching, duplicate-token suppression, substring false-positive guard, and override-only UA when base has none

Example

client = Client(ClientOptions(headers={"User-Agent": "teams-py/1.0"}))
clone = client.clone(ClientOptions(headers={"User-Agent": "myapp/2.0"}))

# Before: "myapp/2.0"  (SDK UA lost)
# After:  "teams-py/1.0 myapp/2.0"
print(clone._options.headers["User-Agent"])

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Original prompt

Implement the change described by PR microsoft/teams.ts#508 ("Merge User-Agent headers when cloning HTTP client") in the Python SDK repository @microsoft/teams.py.

Goal:

• When the HTTP client is cloned (or a new client is created from an existing client/session), ensure that User-Agent headers are merged rather than overwritten.
• Preserve any existing default User-Agent set by the library while also incorporating a user-provided User-Agent (or additional UA tokens) when cloning.

Requirements:

1. Locate the HTTP client implementation and any clone/copy method(s) in the repository.
2. Identify how headers are stored (e.g., requests.Session headers, httpx.Client headers, custom dict) and how cloning currently works.
3. Modify cloning logic so that:
   • If both source and override headers contain User-Agent, the resulting User-Agent should include both (e.g., concatenated with a space, or comma per convention) without duplicating identical values.
   • If only one side has User-Agent, keep it.
   • Header merging should be case-insensitive for the header key.
4. Add/adjust unit tests to cover:
   • Cloning without overrides preserves original User-Agent.
   • Cloning with headers override that includes User-Agent results in merged value.
   • Cloning with headers override without User-Agent leaves original UA intact.
   • Case-insensitive behavior (user-agent, User-Agent).
5. Update any relevant docs or changelog entry if the repo uses one.

Reference:

• PR: Merge User-Agent headers when cloning HTTP client teams.ts#508

Notes:

• Ensure behavior is consistent across sync/async HTTP clients if both exist.
• Keep backward compatibility with existing public APIs.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Can you implement this in @microsoft/teams.py ?

Assistant: I’ve queued up the implementation for microsoft/teams.py and I’m now waiting on your confirmation in the prompt to proceed with making the code changes and opening the PR.

This pull request was created from Copilot chat.

[Copilot]

Pull request overview

Updates the common HTTP Client.clone() behavior so User-Agent headers are merged (instead of overwritten) when callers supply additional headers during cloning, preserving the SDK’s default UA token.

Changes:

• Added _merge_headers(base, overrides) to merge headers with special-case User-Agent concatenation.
• Updated Client.clone() to use _merge_headers() for header merging.
• Added unit tests covering User-Agent merge behavior and edge cases.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
packages/common/src/microsoft_teams/common/http/client.py	Adds header merge helper and switches clone() to UA-aware merging.
packages/common/tests/test_client.py	Adds clone-related tests validating UA preservation/merging and dedup behavior.