[border-agent] simplify forwarding logic to leader

[abtink]

This commit simplifies the CoAP message forwarding logic within the CoapDtlsSession by removing the mPetition and mSeparate boolean flags from the ForwardContext.

The Uri of the request is now stored directly in ForwardContext and used to determine the logic flow, making the code more explicit and easier to understand.

The ForwardToLeader() is only used with kUriLeaderPetition and kUriLeaderKeepAlive, both of which require a separate non-confirmable response in addition to an immediate CoAP Ack (i.e., as if mSeparate is true).

This change removes the need for intermediate flags and simplifies the implementation of ForwardToLeader(), SendErrorMessage(), and the ForwardContext constructor and ToHeader() method. The CoAP message initialization is now more direct, always using kTypeNonConfirmable for forwarded responses and error messages.

[github-actions]

Merging #12114 into main

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[abtink]

/gemini review

[gemini-code-assist]

Code Review

This pull request simplifies the CoAP message forwarding logic by removing intermediate flags (mPetition, mSeparate) and using the request URI directly. This is a great refactoring that makes the code more explicit and easier to follow. The changes are consistent and the logic is sound. I have a couple of minor suggestions to further improve conciseness and debuggability.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.44%. Comparing base (8f11e4a) to head (861f056).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/meshcop/border_agent.cpp	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12114      +/-   ##
==========================================
- Coverage   77.77%   69.44%   -8.34%     
==========================================
  Files         668      667       -1     
  Lines       91356   102812   +11456     
==========================================
+ Hits        71056    71399     +343     
- Misses      20300    31413   +11113     

Files with missing lines	Coverage Δ
src/core/meshcop/border_agent.hpp	45.00% <ø> (ø)
src/core/meshcop/border_agent.cpp	30.15% <0.00%> (+0.86%)	⬆️

... and 241 files with indirect coverage changes

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[Copilot]

Pull Request Overview

This pull request refactors the ForwardToLeader functionality in the Border Agent code to simplify the handling of different URI types. The changes remove separate boolean flags (petition and separate) in favor of storing the URI directly, and consolidate response message handling.

Key changes:

• Replace boolean flags with direct URI storage in ForwardContext
• Simplify SendErrorMessage to always send non-confirmable error responses
• Remove conditional ACK logic since all forwarded messages now send ACKs
• Update response handling to check URI directly instead of using boolean flags

Reviewed Changes

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

File	Description
src/core/meshcop/border_agent.hpp	Updates ForwardContext structure and SendErrorMessage signature to use URI directly
src/core/meshcop/border_agent.cpp	Implements simplified forwarding logic, removes conditional ACK handling, and updates error message generation

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