fix(e2b): add connect json codec support

[guslegend0510]

Summary

Fix E2B envd command execution for environments that only accept application/connect+json (for example Alibaba Cloud FC envd v0.5.2).

Changes

• Add E2bCodec with default PROTO
• Make E2bFilesystemSpec / E2bSandboxClientOptions configurable for codec selection
• Persist codec through E2bSandboxClient / E2bSandboxState
• Update E2bEnvdProcessClient to emit connect+json requests and parse JSON responses when configured
• Add focused tests for proto/json request envelope and response frame parsing

Verification

• mvn -DskipTests compile
• mvn test -Dtest=E2bEnvdProcessClientTest,E2bSnapshotRefsTest

Closes #1842

[codecov]

Codecov Report

❌ Patch coverage is 70.24793% with 36 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...e/extensions/sandbox/e2b/E2bEnvdProcessClient.java	78.21%	9 Missing and 13 partials ⚠️
...scope/extensions/sandbox/e2b/E2bSandboxClient.java	0.00%	7 Missing ⚠️
...tscope/extensions/sandbox/e2b/E2bSandboxState.java	0.00%	4 Missing ⚠️
...cope/extensions/sandbox/e2b/E2bFilesystemSpec.java	0.00%	2 Missing ⚠️
...xtensions/sandbox/e2b/E2bSandboxClientOptions.java	75.00%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[AgentScopeJavaBot]

🤖 AI Review

This PR adds application/connect+json codec support for the E2B envd process.Process/Start endpoint, enabling compatibility with envd implementations (e.g., Alibaba Cloud FC envd v0.5.2) that only accept JSON. The change is well-structured: a new E2bCodec enum is threaded through E2bSandboxClientOptions, E2bSandboxState, and E2bFilesystemSpec; the core encoding/decoding logic in E2bEnvdProcessClient branches on the codec with clean helper methods; backward compatibility is preserved (default remains PROTO). Tests cover the key happy-path scenarios. One defensive-programming gap around Base64 decoding and a minor test-coverage gap are noted below.

[AgentScopeJavaBot]

🤖 AI Review

This PR adds application/connect+json codec support for the E2B envd process.Process/Start endpoint, enabling compatibility with envd implementations (e.g., Alibaba Cloud FC envd v0.5.2) that only accept JSON. The change is well-structured: a new E2bCodec enum is threaded through E2bSandboxClientOptions, E2bSandboxState, and E2bFilesystemSpec; the core encoding/decoding logic in E2bEnvdProcessClient branches on the codec with clean helper methods; backward compatibility is preserved (default remains PROTO). Tests cover the key happy-path scenarios. One defensive-programming gap around Base64 decoding and a minor test-coverage gap are noted below.

[AgentScopeJavaBot]

All previously raised review comments have been addressed.