Let check_availability use what the reactive half saw

The watchlist is read before answering, so a crossing that happened twenty
minutes ago is part of the answer.

It also fixes a contradiction the agent was publishing: the catalog domain
caches reads for 60 seconds, so an agent woken by an event reads a figure taken
up to a minute earlier — it answered "68 in stock, above the threshold" and
"it crossed the threshold, from 68" in the same sentence. A movement is the
catalog's own dated statement; a read is an undated copy. The dated one wins,
and the answer says so.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

workflows/README.md

@@ -89,6 +89,52 @@ and through the A2A facade, `escalate: true` becomes a task in state **failed**
 rather than a completed one — the honest shape for "a human has to look at
 this".
 
+### It now knows what the reactive half saw
+
+`check-availability` reads the watchlist before answering, so a crossing that
+happened twenty minutes ago is part of the answer:
+
+```
+"Peut-on promettre S12_1099 ?"
+  → "No — 1968 Ford Mustang (S12_1099) is down to 8 … It crossed the threshold
+     at 06:18:24 (driven by orders), from 68."
+```
+
+"It fell below this afternoon, under demand" is a different decision from "it
+has been sitting below for a month", and only the event carries that.
+
+The watchlist is read over an in-cluster call to the stock-watch workflow's own
+webhook — its data lives in that workflow and there is no other way in. The node
+is `onError: continueRegularOutput`: an availability answer must not depend on
+the watchlist being up.
+
+### A dated fact beats an undated read
+
+The two figures can disagree, and when they do the **read** is the wrong one.
+This was not theoretical — the agent answered, in one sentence:
+
+```
+"68 in stock, above the reorder threshold of 50 … It crossed the threshold, from 68."
+```
+
+The catalog domain caches reads for **60 seconds**. An agent woken by an event
+reacts in seconds and then reads a figure taken up to a minute earlier. A
+movement is the catalog's own *dated* statement that stock went from X to Y; a
+read is an undated copy. So the movement wins, and the answer says the basis
+changed:
+
+```
+Basis: the latest stock movement, which is more recent than the catalog read
+```
+
+Measured after the fix, with the cache deliberately warmed at 38 and the true
+stock moved to 8 inside the window: the answer said **8**.
+
+This only helps a reference the reactive half is already watching. For any
+other, the read stands with whatever staleness it has, and nothing in the
+workflow can tell — which is worth remembering before treating any single read
+as current.
+
 ## approvisionnement-periodic-reorder
 
 The periodic half. A schedule trigger at 06:00, deliberately periodic rather