chore(main): release 1.4.0

[adk-java-releases-bot]

🤖 I have created a release beep boop

1.4.0 (2026-05-29)

Features

• Add GcsOffloader for asynchronously uploading content to Google Cloud Storage (51c9d1a)
• Add GcsOffloader for asynchronously uploading content to Google Cloud Storage (5bad20a)
• Add GcsOffloader for asynchronously uploading content to Google Cloud Storage (a1d2c1c)
• Add JSON cycle detection (1685a4e)
• Add streaming support for ChatCompletionsHTTPClient (384a0c5)
• Add telemetry and metrics recording capabilities (cc3b9ce)
• Add tools and toolset to use SkillSource in ADK agents (198b2fb)
• Add tools and toolset to use SkillSource in ADK agents (5ee51fd)
• Add tools and toolset to use SkillSource in ADK agents (83a4b71)
• Introduce max span limit to ApiServerSpanExporter (ae13073)
• refactor OpenTelemetry (OTel) instrumentation within the ADK core, moving from manual span management to structured helper classes (e6fe9aa)

Bug Fixes

• adjust default ToolExecutionMode to SEQUENTIAL as it was actual and widely used behavior for all ADK Java users before parallel tool execution fix (fe88217)
• inject Dev UI tracer into core engine for embedded telemetry (8bccc3b)
• introduce PARALLEL_SUBSCRIBE ToolExecutionMode; restore previous PARALLEL semantics (d3e7f31)
• mcp: honor custom URL sub-paths in StreamableHttpServerParameters (a0c4b7b)
• pre-merge stateDelta before onUserMessageCallback in Runner (f1155ec)
• Resolve IllegalArgumentException for text MIME types in LangChain4j adapter (6ad2043)
• revert "Suppress empty-text-only chunks from streaming responses while preserving carried metadata" (69638df)
• route HITL confirmation back to originating sub-agent in workflow agents (d608909)
• run tools concurrently in PARALLEL ToolExecutionMode (020499b)
• Suppress empty-text-only chunks from streaming responses while preserving carried metadata (b4791ef)

Documentation

• clarify LlmAgent composition for workflow agents (49ff63b)

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