chore: WIP... too much in 1 go

[vorburger]

Relates to #1854 and #1857... but NOK, as is.

Next step: Break this up more gradually, into:

1. Switch the resolver of rules_jvm_external from coursier to maven

2. Pin & bump MCP

3. Bump ADK

[gemini-code-assist]

Summary of Changes

Hello @vorburger, 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 represents a work-in-progress effort to refactor and update the project's dependency management. The primary goals are to transition the rules_jvm_external resolver to Maven, pin and bump the Model Context Protocol (MCP) library, and update the Google ADK. Additionally, a wide array of other library versions have been adjusted, some to newer releases and others to older, potentially more stable, versions, indicating a broader dependency cleanup and alignment.

Highlights

• Dependency Resolver Switch: The rules_jvm_external resolver has been switched from coursier to maven in MODULE.bazel and its handlebars template.
• Google ADK Update: Google ADK dependencies (google-adk, google-adk-dev, google-adk-langchain4j) have been updated and pinned to version e60bddf6502bbfac5af3fb993acc100439c0d90f across MODULE.bazel, MODULE.bom.handlebars.yaml, and docs/dev/dependencies.txt.
• MCP Integration: The io.modelcontextprotocol.sdk:mcp:0.11.3 dependency has been introduced and explicitly excluded from google-adk and google-adk-langchain4j to prevent potential conflicts, as noted in issue Cannot upgrade (bump) MCP SDK (which is pull transitively via ADK) because of rules_jvm_external problem #1857.
• Extensive Dependency Version Adjustments: Numerous other dependencies have seen version changes in docs/dev/dependencies.txt, including updates and some downgrades for libraries such as Jackson, Google Cloud APIs, Netty, OpenTelemetry, Apache Tika (to a beta version), and various Apache Commons components.

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[gemini-code-assist]

Code Review

This pull request attempts to update several key dependencies, including ADK and MCP, and switches the Bazel resolver. As you've noted in the title and description, this is a very large set of changes with significant ripple effects across the dependency tree. The update to ADK, in particular, seems to be causing a large number of transitive dependencies to be downgraded, some by multiple major versions. This introduces a high risk of breaking changes, regressions, and pulling in known security vulnerabilities from older library versions. Your plan to break this up into smaller, more gradual pull requests is absolutely the right approach to manage these risks. I've added a specific comment highlighting the extent of the downgrades for visibility.

[gemini-code-assist]

This diff, and many others in this file, show a significant number of dependency downgrades as a result of the ADK bump. For example:

• jackson-core is downgraded from 2.19.2 to 2.13.5.
• langchain4j-core is downgraded from 1.6.0 to 1.4.0.
• netty-transport-native-epoll is downgraded from 4.1.116.Final to 4.1.46.Final.
• tika artifacts are downgraded from 3.0.0 to 3.0.0-BETA2.

Such major version downgrades can introduce breaking API changes and re-introduce bugs or security vulnerabilities that were fixed in later versions. This highlights the risk of the current approach and strongly supports your plan to break this change into smaller, more manageable pieces to better understand and mitigate the impact of each dependency update.

[vorburger]

Replaced with #1859 and #1861, and later #1860.