chore(epic/1.0_breaking_changes): release sdk 1.0.0-alpha.0

[a2a-bot]

🤖 I have created a release beep boop

1.0.0-alpha.0 (2026-05-11)

See the v0.3 -> v1.0-alpha.0 migration guide.

Note: Enabling backward compatibility with v0.3 is tracked in #452.

⚠ BREAKING CHANGES

• Drop support for node 18 (#368)
• Make ServerCallContext parameter mandatory across all places (#405)
• Remove JSON-RPC client (#353)
• Remove transport-specific exports (#404)
• Update codebase to use A2A 1.0.0 data model (#375)
• Remove A2AExpressApp (#363)

Features

• Add A2A Version Header (#422) (b5f3db7)
• Add cache-headers logic to the agent card handler (#435) (955b52b)
• Add resource scoping (#450) (c527086)
• Add support for custom authentication scheme and credentials in auth-headers (#430) (5a4389b)
• AgentCardSignature support (#448) (4a41a8c)
• Enforce events ordering (#437) (157cf48)
• Enriched Error Model (#427) (c130778)
• Implement listTasks method (#383) (7d4c472)
• Send current task as the first event after subscribing to it (#418) (4bfcf5f)
• Support multi-tenancy (#419) (1877877)

Code Refactoring

• remove A2AExpressApp (#363) (0b84728)

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[github-actions]

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[gemini-code-assist]

Code Review

This pull request updates the project version to 0.3.9 across the manifest and package files while adding a comprehensive changelog entry detailing numerous breaking changes, features, and bug fixes. Feedback indicates that changing the version from 0.3.13 to 0.3.9 is a version downgrade that will cause issues with package managers and is inconsistent with the breaking changes described. Additionally, the new changelog entry is incorrectly placed at the top of the file, creating an out-of-order and duplicate version history.

[bartek-gralewicz]

Note: The migration guide is linked under https://github.com/a2aproject/a2a-js/blob/v1.0.0-alpha.0/docs/migration-guide.md which is a dead link before the creation of v1.0.0-alpha.0 tag. This will auto-fix itself when we tag the alpha after release.

[a2a-bot]

🤖 Created releases:

• sdk-v1.0.0-alpha.0

🌻