What

Resolve the value_store in-place deserialization placeholder in message_container.

Part of kcenon/common_system#684.

The 2026-05-21 analysis found TODO comments in src/messaging/message_container.cpp indicating that in-place deserialization for value_store is currently a placeholder.

Why

container_system is the shared data/serialization layer for higher-level systems. A placeholder in deserialization behavior can become a hidden correctness or performance gap if downstream systems assume the operation is fully implemented.

Where

• src/messaging/message_container.cpp
• include/kcenon/container/value_store.h
• include/kcenon/container/messaging/message_container.h
• Serializer tests under tests/
• Messaging integration tests, if present

How

Approach

1. Inspect the placeholder code path and confirm whether the intended behavior is still required.
2. If required, implement in-place deserialization for value_store without changing the public API unexpectedly.
3. If not required, remove the placeholder path and document the supported alternative.
4. Add tests covering round-trip serialization/deserialization and failure handling for malformed input.
5. Update README/docs if the behavior is user-facing.

Acceptance Criteria

• No TODO/placeholder remains for value_store in-place deserialization
• Round-trip tests cover the affected message_container path
• Malformed input returns the established error/result behavior rather than partial state mutation
• Existing serializers continue to pass their tests
• [EPIC] Ecosystem hardening follow-up from 2026-05-21 analysis common_system#684 receives the final container summary

Verification

• ctest for container serialization/messaging tests passes
• Any new tests fail before the implementation and pass after it