Add MAIN-to-RX acknowledgement channel

docs/handoff/TX_AGENT_USAGE.md

@@ -2,7 +2,7 @@
 
 ## Purpose
 
-tools/tx_agent_watcher.py is an ordinary local Python process. It polls the small RX result on origin/rx-node. It does not call an LLM and does not open HackRF hardware.
+tools/tx_agent_watcher.py is an ordinary local Python process. It polls the small RX result on origin/rx-node and publishes small acknowledgements to origin/tx-node. It does not call an LLM and does not open HackRF hardware.
 
 ## Start
 
@@ -10,7 +10,7 @@ From the repository root, double-click:
 
     tools\start_tx_watcher.cmd
 
-The visible console polls every 5 seconds. A missing rx-node branch or invalid result is reported. No model runs while polling.
+The visible console polls every 5 seconds. A missing rx-node or tx-node branch, an invalid result or an acknowledgement push failure is reported. No model runs while polling or publishing.
 
 ## Result history cursor
 
@@ -20,13 +20,29 @@ The watcher stores `last_processed_rx_node_commit` in `.local\tx_agent_watcher_s
 
 It reads `RX_RESULT.json` from each exact commit and processes the commits from oldest to newest. READY therefore remains observable when READY and COMPLETE are both published between two polling cycles.
 
-The cursor advances only after that commit has been read, validated and handled successfully. A malformed intermediate commit blocks later commits until the defect is corrected. A non-fast-forward rewrite of `rx-node` is rejected. Duplicate result content is suppressed, but its commit is still marked as processed.
+The cursor advances only after that commit has been read, validated, handled and, when required, acknowledged successfully. A failed acknowledgement push leaves the RX commit unprocessed so that the next poll retries it. A malformed intermediate commit blocks later commits until the defect is corrected. A non-fast-forward rewrite of `rx-node` is rejected. Duplicate result content is suppressed, but its commit is still marked as processed.
 
 State format version 2 retains the existing digest and authorization fields and adds `last_seen_commit` and `last_processed_rx_node_commit`. A version-1 digest-only state is mapped to the newest matching commit in the existing result history. Back up the local state before manual recovery; do not delete it blindly.
 
+## MAIN acknowledgements
+
+After it handles a channel-test READY or COMPLETE event, the watcher publishes a strict acknowledgement to origin/tx-node. Each acknowledgement binds the exact `SOURCE_RX_COMMIT`, canonical `SOURCE_RX_DIGEST` and RX result `SOURCE_HEAD`. The channel-test states are:
+
+    CHANNEL_READY_OBSERVED
+    CHANNEL_COMPLETE_OBSERVED
+
+The tx-node branch is independent of video-development. Every commit tree may contain only:
+
+    docs/handoff/results/TX_RESULT.json
+    docs/handoff/results/TX_RESULT.md
+
+Each file is limited to 64 KiB. Before committing, the publisher compares the complete staged path set with this allowlist. It suppresses an acknowledgement that already exists for the same task, state, RX commit, digest, source HEAD and RF safety values. The RX laptop scans the full tx-node history from oldest to newest, so two acknowledgements published between polls remain observable.
+
+The acknowledgement operation is ordinary Python and Git. It does not invoke ChatGPT, Codex or another model. It stores no IQ, video, waveform, source code, large logs or local state on tx-node.
+
 ## READY and RED approval
 
-RF_HANDOFF_CHANNEL_TEST_001 READY and COMPLETE states are recorded without a RED prompt and never open the production gate.
+RF_HANDOFF_CHANNEL_TEST_001 READY and COMPLETE states are recorded and acknowledged without a RED prompt and never open the production gate.
 
 For a fresh valid RF001A_OTA_CAPTURE_003 READY result, the watcher checks the expected source HEAD, current origin/rx-node commit, common clock and capture window. It then prints the task ID, capture start and expected end and asks for: