diff --git a/specifier-prompt.md b/specifier-prompt.md
index 40b793f..9172d0d 100644
--- a/specifier-prompt.md
+++ b/specifier-prompt.md
@@ -341,6 +341,17 @@ that a single user-facing feature may require specs in more than one component.
     following feed, topic feed, notifications, search, profile, recent profiles)
     use 50. The pure paginated controllers share a `PaginatedPage` base; profile,
     search, and recent-profiles gained Previous/Next controls in the same change.
+19. **Do not use Node's `Buffer` global in client service code (real bug found).**
+    `memo-follow.js` and `memo-mute.js` used `Buffer.from(hash160, 'hex')` and
+    passed a Node `Buffer` to `wallet.sendOpReturn`; in a real browser `Buffer`
+    is undefined, so clicking Follow/Mute threw `Buffer is not defined` *after*
+    `getUtxos()` succeeded but *before* the transaction was composed. Node-based
+    unit/acceptance tests masked it because `Buffer` is a global under Node and
+    the fake wallet just recorded the passed value. Build binary Memo payloads
+    as a `Uint8Array` from the `./hex` `hexToBytes` helper (see `memo-reply.js`,
+    `memo-txid-action.js`, and now `memo-state-action.js`). To catch regressions,
+    unit-test that broadcast succeeds with `global.Buffer` temporarily deleted.
+    Fixed in the binary-payload-broadcast job (`984e691`).
 
 ---
 
@@ -378,9 +389,10 @@ At the end of each session, update this file:
 - Note the current `master` HEAD commit.
 - State the next feature to work on.
 
-Current `master` HEAD: `cfe6711` (merged architect's page-size-50 job — every
-paginated page now requests 50 items instead of 100, pagination controls added
-to search/profile/recent-profiles, controllers refactored onto `PaginatedPage`;
-verified client build OK + 280 unit passing + 40 property passing + lint clean +
-all 22 acceptance suites pass incl. the new page-size suite).
+Current `master` HEAD: `984e691` (merged architect's binary-payload-broadcast job —
+client follow/unfollow and mute/unmute broadcast the target's raw 20-byte
+hash160 as a browser-safe `Uint8Array` payload, no longer crashing with
+`Buffer is not defined`; follow/mute refactored onto a shared `MemoStateAction`
+base. Verified client build OK + 280 unit passing + lint clean + all 23
+acceptance suites pass, including the new `binary-payload-broadcast` suite).
 Next action: **ask the user for the next front-end improvement to spec**.
diff --git a/specs/feature-backlog.md b/specs/feature-backlog.md
index 24560ae..01030b8 100644
--- a/specs/feature-backlog.md
+++ b/specs/feature-backlog.md
@@ -31,6 +31,14 @@ focus is **front-end improvements** to `psf-memo-client` (the React SPA).
 
 ## Recently completed
 
+- **Binary hash160 broadcast payloads (2026-09-04):** client follow/unfollow
+  and mute/unmute now broadcast the target's raw 20-byte hash160 as the
+  OP_RETURN payload, built as a browser-safe `Uint8Array` from the `hexToBytes`
+  helper instead of Node's `Buffer` global (which crashed in a real browser
+  with `Buffer is not defined`). Follow/mute/unfollow/unmute were consolidated
+  onto a shared `MemoStateAction` base. Spec:
+  `psf-memo-client/specs/binary-payload-broadcast.feature`. Merged to `master`
+  at `984e691`.
 - **Page size 50 (2026-09-04):** every paginated page in the client now requests 50
   items per page instead of 100 to cut payload size and improve page load times.
   Covers the recent feed, following feed, topic feed, notifications, search,