docs: document the data_as_of response envelope

README.md

@@ -23,6 +23,44 @@ See [COOKBOOK.md](COOKBOOK.md) for the full catalog (added in Phase 1+).
 Phase 0 ships the foundation and one canonical recipe:
 [01-gex-dashboard](notebooks/tier-a-hooks/01-gex-dashboard.ipynb).
 
+## Data provenance: `data_as_of`
+
+Every FlashAlpha API response carries `data_as_of`, reporting when each upstream feed last
+delivered to the node that answered, plus `endpoint_version` identifying the deployment
+that produced it.
+
+```json
+"endpoint_version": "2026.08.25",
+"data_as_of": {
+  "node": "fa2",
+  "equity_feed": "2026-08-25T18:48:58.204Z",
+  "equity_options_feed": "2026-08-25T18:48:57.900Z",
+  "index_feed": null,
+  "index_options_feed": null,
+  "futures_feed": null,
+  "futures_options_feed": null,
+  "flow_feed": "2026-08-25T18:48:55.100Z",
+  "oi_feed": "2026-08-24T20:00:00.000Z",
+  "macro_feed": "2026-08-25T18:45:00.000Z"
+}
+```
+
+Spot and options are reported separately because they arrive over different pipes and fail
+independently - an index chain can be current while the index level behind it is not, and
+one timestamp cannot express that.
+
+Read each feed against its **own cadence**, not against `as_of`. `oi_feed` at the previous
+session's close is correct: settled open interest is published once per session, so on a
+Monday the newest figure that exists is Friday's. An options feed an hour behind during
+the regular session is not correct. A `null` means that node has not seen that feed, not
+that it is broken.
+
+The field evidences that a feed delivered recently. It does not assert that every contract
+in a chain is equally current: an illiquid strike may not have quoted for hours while its
+feed is healthy.
+
+Full reference: <https://flashalpha.com/docs/lab-api-overview#response-envelope>
+
 ## Authoring a new recipe
 
 ```bash

llms.txt

@@ -4,6 +4,18 @@
 
 The repository at https://github.com/FlashAlpha-lab/flashalpha-examples hosts the cookbook itself. The FlashAlpha API it calls is documented separately at https://lab.flashalpha.com/llms.txt — both the live surface (`api.flashalpha.com`) and the historical replay surface (`historical.flashalpha.com`) return identical response shapes; backtest recipes use historical, real-time recipes use live.
 
+## Data provenance
+
+Every FlashAlpha API response carries `data_as_of`: when each upstream feed last delivered
+to the node that answered - equity and index spot, their option chains, futures and futures
+options, the classified trade tape, settled open interest, and the macro series, each
+reported separately because they arrive over different pipes and fail independently. `null`
+means that node has not seen that feed, not that it is broken. Read each feed against its
+own cadence: settled open interest dated to the previous session's close is correct, while
+an options feed an hour behind during the regular session is not. `endpoint_version`
+identifies the deployment. Full reference:
+https://flashalpha.com/docs/lab-api-overview#response-envelope
+
 ## Quick start
 
 ```bash