docs: Add specification versioning guidelines

[madankumarpichamuthu]

Adds Section 3.6.5 to specification.md documenting when to use patch vs minor vs major releases for specification changes. This provides clear guidance for contributors on version increment rules:

• Patch: Documentation/comments only (non-functional changes)
• Minor: Any a2a.proto changes (functional changes)
• Major: Breaking changes

Also adds brief cross-reference in CONTRIBUTING.md for discoverability.

Changes:

• Added Section 3.6.5 Specification Versioning to docs/specification.md
• Includes semantic versioning rules and decision tree
• Added Versioning section to CONTRIBUTING.md with link to spec

This addresses the ambiguity identified by the TSC about when contributors should use different version increments.

Fixes #1357

[gemini-code-assist]

Summary of Changes

Hello @madankumarpichamuthu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces clear and comprehensive guidelines for versioning the A2A specification, aiming to resolve ambiguity for contributors and maintainers regarding when to increment patch, minor, or major versions. It standardizes the approach to versioning based on the nature of changes, ensuring consistency and predictability in specification evolution.

Highlights

• New Specification Versioning Guidelines: A new section (3.6.5) has been added to docs/specification.md detailing comprehensive guidelines for specification versioning, clarifying when to use patch, minor, or major releases based on Semantic Versioning principles.
• Semantic Versioning Rules Defined: The new guidelines explicitly define criteria for Patch (non-functional changes), Minor (functional changes to a2a.proto or protocol behavior), and Major (breaking changes) releases, including a decision tree for contributors.
• Contributor Guidance Update: A new 'Versioning' section has been added to CONTRIBUTING.md, providing a brief overview of the semantic versioning rules and a direct link to the detailed specification versioning guidelines for easy discoverability.

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[madankumarpichamuthu]

@darrelmiller i hope, this is what you had in mind for issue #1357?

[gemini-code-assist]

Code Review

This pull request is a great addition, providing clear versioning guidelines for the A2A specification. The new sections in CONTRIBUTING.md and specification.md will be very helpful for contributors.

My review includes a couple of suggestions to refine the logic in the new guidelines to ensure they are fully consistent and cover all change types correctly. Specifically, I've proposed updates to the decision tree in specification.md to handle non-functional changes (like comment-only changes in .proto files or build script updates) correctly as patch releases. I've also suggested a small update to the summary in CONTRIBUTING.md to align with the more detailed rules.

[holtskinner]

@gemini-code-assist review

[gemini-code-assist]

Code Review

This pull request introduces clear and much-needed versioning guidelines for the specification. The changes in specification.md are well-detailed, providing rules for patch, minor, and major version increments, along with a helpful decision tree for contributors. The corresponding summary and link in CONTRIBUTING.md improve discoverability. Overall, this is an excellent addition to the documentation. I've left one minor suggestion to fix a markdown formatting issue.