Bump the batch payload codec to schema v4 with separate meter-time and UTC anchors, then use meter seconds for sparse batch slotting and receiver reconstruction.
Update the current 868 MHz bench configuration, allow ACKs from configured receiver short IDs, improve AP-to-STA recovery, quiet the test build, and document the changed protocol in the README.
- Make include/ the canonical declarations for data_model/html_util/json_codec and convert dd3_legacy_core header copies to thin forwarders.
- Add stable public forwarders for app_context/receiver_pipeline/sender_state_machine and update refactor smoke test to stop using ../../src includes.
- Force-link dd3_legacy_core from setup() to ensure deterministic PlatformIO LDF linking across firmware envs.
- Refresh docs (README, Requirements, docs/TESTS.md) to reflect current module paths and smoke-test include strategy.
acidburns