POC: Bind AgentCore sessions to one ACS instance using a stable identity

AGENTS.md

@@ -35,6 +35,11 @@ Before starting the implementation or review of any request, you MUST REVIEW the
 - Update API proto: `make update-go-api`
 - Always include `-tags test_dep` when running tests. Include the `integration` tag only for integration tests.
 
+## Code Conventions
+
+- Keep receiver methods in their existing implementation files and unit tests in the corresponding owner test files. Do not create feature files that mix methods or test suites from unrelated owners.
+- Use getter methods for reads whenever available, including protobuf fields. Use direct field access for assignments.
+
 ## Development Workflow
 
 1. Inspect surrounding code, tests, and configuration before making changes.