docs: document the data_as_of response envelope

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.

Nine feeds are reported separately - equity and index spot, their option
chains, futures and futures options, the classified trade tape, settled
open interest, and the macro series - 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.

The section covers how to read it, not just what it is: each feed against
its OWN cadence rather than against as_of. Settled open interest dated to
the previous session's close is correct, because it is published once per
session - on a Monday the newest figure that exists is Friday's. An
options feed an hour behind during the regular session is not. A null
means that node has not seen that feed, not that it is broken.

The limit is stated alongside the claim: the field evidences that a feed
delivered recently, not that every contract in a chain is equally current.

Documentation only. No code changes.

Author: tdobrowolski1

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": "2026-08-22T20:00:00.000Z",
+  "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