diff --git a/canvas/src/components/A2ATopologyOverlay.tsx b/canvas/src/components/A2ATopologyOverlay.tsx
index 58f2d976..53920d4a 100644
--- a/canvas/src/components/A2ATopologyOverlay.tsx
+++ b/canvas/src/components/A2ATopologyOverlay.tsx
@@ -1,9 +1,10 @@
 'use client';
 
-import { useEffect, useMemo, useCallback } from "react";
+import { useEffect, useMemo, useCallback, useRef } from "react";
 import { type Edge, MarkerType } from "@xyflow/react";
 import { api } from "@/lib/api";
 import { useCanvasStore } from "@/store/canvas";
+import { useSocketEvent } from "@/hooks/useSocketEvent";
 import type { ActivityEntry } from "@/types/activity";
 
 // ── Constants ─────────────────────────────────────────────────────────────────
@@ -11,9 +12,6 @@ import type { ActivityEntry } from "@/types/activity";
 /** 60-minute look-back window for delegation activity */
 export const A2A_WINDOW_MS = 60 * 60 * 1000;
 
-/** Polling interval — refresh edges every 60 seconds */
-export const A2A_POLL_MS = 60 * 1_000;
-
 /** Threshold for "hot" edges: < 5 minutes → animated + violet stroke */
 export const A2A_HOT_MS = 5 * 60 * 1_000;
 
@@ -131,6 +129,20 @@ export function buildA2AEdges(
  * `a2aEdges`. Canvas.tsx merges these with topology edges and passes the
  * combined list to ReactFlow.
  *
+ * Update shape (issue #61 Stage 2, replaces the 60s polling loop):
+ *  - On mount (when showA2AEdges): one HTTP fan-out per visible workspace
+ *    (delegation rows, 60-min window). Bootstraps the local row buffer.
+ *  - Steady state: subscribes to ACTIVITY_LOGGED via useSocketEvent.
+ *    Each delegation event from a visible workspace is appended to the
+ *    buffer; edges are re-derived via the existing buildA2AEdges helper.
+ *  - showA2AEdges toggle off: clears edges + buffer.
+ *  - Visible-ID-set change: re-bootstraps so a freshly-shown workspace
+ *    backfills its 60-min history (existing visibleIdsKey selector
+ *    behaviour preserved — that's the 2026-05-04 render-loop fix).
+ *
+ * No interval poll. The singleton ReconnectingSocket already owns
+ * reconnect / backoff / health-check; useSocketEvent inherits those.
+ *
  * Mount this inside CanvasInner (no ReactFlow hook dependency).
  */
 export function A2ATopologyOverlay() {
@@ -157,7 +169,9 @@ export function A2ATopologyOverlay() {
   // the symptom of this re-render storm.
   //
   // The fix is purely the dependency-stability change here; the fetch
-  // logic is unchanged.
+  // logic is unchanged. Post-#61 the polling-driven fetch is gone, but
+  // the visibleIdsKey gate is still required so a peer-discovery write
+  // doesn't trigger a wasteful re-bootstrap.
   const visibleIdsKey = useCanvasStore((s) =>
     s.nodes
       .filter((n) => !n.hidden)
@@ -171,16 +185,42 @@ export function A2ATopologyOverlay() {
     [visibleIdsKey]
   );
 
-  // Fetch delegation activity for all visible workspaces and rebuild overlay edges.
-  const fetchAndUpdate = useCallback(async () => {
+  // Local rolling buffer of delegation rows. Pruned by A2A_WINDOW_MS on
+  // each rebuild so a long-lived session doesn't accumulate unbounded
+  // history. The buffer's high-water mark is approximately:
+  //    visibleIds.length × bootstrap-fetch-limit (500) + WS arrivals
+  // Real-world ceiling: ~3000 entries at the 60-min boundary, all of
+  // which buildA2AEdges aggregates into at most N² edges.
+  const bufferRef = useRef<ActivityEntry[]>([]);
+  // visibleIdsRef gives the WS handler the latest visible-ID set without
+  // re-subscribing on every render. The bus listener is registered
+  // exactly once per mount; subscriber-side filtering reads from this ref.
+  const visibleIdsRef = useRef(visibleIds);
+  visibleIdsRef.current = visibleIds;
+
+  // Re-derive overlay edges from the current buffer + push to store.
+  // Prunes by A2A_WINDOW_MS first so memory stays bounded across long
+  // sessions and the aggregation cost stays O(window-size).
+  const recomputeAndPush = useCallback(() => {
+    const cutoff = Date.now() - A2A_WINDOW_MS;
+    bufferRef.current = bufferRef.current.filter(
+      (r) => new Date(r.created_at).getTime() > cutoff
+    );
+    setA2AEdges(buildA2AEdges(bufferRef.current));
+  }, [setA2AEdges]);
+
+  // Bootstrap fan-out — one HTTP per visible workspace. Replaces the
+  // 60s polling loop entirely. Race-aware: any WS arrivals that landed
+  // in the buffer DURING the fetch (between the await and resume) are
+  // preserved by id-dedup-with-fetched-first ordering.
+  const bootstrap = useCallback(async () => {
     if (visibleIds.length === 0) {
+      bufferRef.current = [];
       setA2AEdges([]);
       return;
     }
     try {
-      // Fan-out — one request per visible workspace.
-      // Per-request failures are swallowed so one broken workspace doesn't blank the overlay.
-      const allRows = (
+      const fetchedRows = (
         await Promise.all(
           visibleIds.map((id) =>
             api
@@ -192,24 +232,76 @@ export function A2ATopologyOverlay() {
         )
       ).flat();
 
-      setA2AEdges(buildA2AEdges(allRows));
+      // Merge: fetched rows first, then any in-flight WS arrivals that
+      // accumulated during the await. Dedup by id so rows that appear
+      // in both paths are not double-counted in the aggregation.
+      const merged = [...fetchedRows, ...bufferRef.current];
+      const seen = new Set<string>();
+      bufferRef.current = merged.filter((r) => {
+        if (seen.has(r.id)) return false;
+        seen.add(r.id);
+        return true;
+      });
+      recomputeAndPush();
     } catch {
       // Overlay failure is non-critical — canvas remains functional
     }
-  }, [visibleIds, setA2AEdges]);
+  }, [visibleIds, setA2AEdges, recomputeAndPush]);
 
   useEffect(() => {
     if (!showA2AEdges) {
-      // Clear edges immediately when toggled off
+      // Clear edges + buffer immediately when toggled off
+      bufferRef.current = [];
       setA2AEdges([]);
       return;
     }
+    void bootstrap();
+  }, [showA2AEdges, bootstrap, setA2AEdges]);
 
-    // Initial fetch, then poll every 60 s
-    void fetchAndUpdate();
-    const timer = setInterval(() => void fetchAndUpdate(), A2A_POLL_MS);
-    return () => clearInterval(timer);
-  }, [showA2AEdges, fetchAndUpdate, setA2AEdges]);
+  // Live-update path. Filters server-side ACTIVITY_LOGGED events down
+  // to delegation initiations from visible workspaces and appends each
+  // into the rolling buffer, re-deriving edges via buildA2AEdges.
+  //
+  // Only `method === "delegate"` rows count — the same filter
+  // buildA2AEdges applies — so delegate_result rows arriving over the
+  // wire don't double-count.
+  useSocketEvent((msg) => {
+    if (!showA2AEdges) return;
+    if (msg.event !== "ACTIVITY_LOGGED") return;
+
+    const p = (msg.payload || {}) as Record<string, unknown>;
+    if (p.activity_type !== "delegation") return;
+    if (p.method !== "delegate") return;
+
+    const wsId = msg.workspace_id;
+    if (!visibleIdsRef.current.includes(wsId)) return;
+
+    // Synthesise an ActivityEntry from the WS payload so buildA2AEdges
+    // (which the bootstrap path also feeds) handles it identically.
+    const entry: ActivityEntry = {
+      id:
+        (p.id as string) ||
+        `ws-push-${msg.timestamp || Date.now()}-${wsId}`,
+      workspace_id: wsId,
+      activity_type: "delegation",
+      source_id: (p.source_id as string | null) ?? null,
+      target_id: (p.target_id as string | null) ?? null,
+      method: "delegate",
+      summary: (p.summary as string | null) ?? null,
+      request_body: null,
+      response_body: null,
+      duration_ms: (p.duration_ms as number | null) ?? null,
+      status: (p.status as string) || "ok",
+      error_detail: null,
+      created_at:
+        (p.created_at as string) ||
+        msg.timestamp ||
+        new Date().toISOString(),
+    };
+
+    bufferRef.current = [...bufferRef.current, entry];
+    recomputeAndPush();
+  });
 
   // Pure side-effect — renders nothing
   return null;
diff --git a/canvas/src/components/CommunicationOverlay.tsx b/canvas/src/components/CommunicationOverlay.tsx
index 10d105db..dfe0625e 100644
--- a/canvas/src/components/CommunicationOverlay.tsx
+++ b/canvas/src/components/CommunicationOverlay.tsx
@@ -3,6 +3,7 @@
 import { useState, useEffect, useCallback, useRef } from "react";
 import { useCanvasStore } from "@/store/canvas";
 import { api } from "@/lib/api";
+import { useSocketEvent } from "@/hooks/useSocketEvent";
 import { COMM_TYPE_LABELS } from "@/lib/design-tokens";
 
 interface Communication {
@@ -18,32 +19,71 @@ interface Communication {
   durationMs: number | null;
 }
 
+/** Workspace-server `ACTIVITY_LOGGED` payload shape. Pulled out so the
+ *  WS handler below has a typed view of the same fields the HTTP
+ *  bootstrap consumes — drift between the two paths is a class of bug
+ *  AgentCommsPanel hit historically. */
+interface ActivityLoggedPayload {
+  id?: string;
+  activity_type?: string;
+  source_id?: string | null;
+  target_id?: string | null;
+  workspace_id?: string;
+  summary?: string | null;
+  status?: string;
+  duration_ms?: number | null;
+  created_at?: string;
+}
+
+/** Fan-out cap for the bootstrap HTTP fetch on mount / on visibility
+ *  re-open. Kept at 3 (carried over from the 2026-05-04 fix) so a
+ *  freshly-mounted overlay on a 15-workspace tenant only spends 3
+ *  round-trips bootstrapping. Live updates after that arrive via the
+ *  WS subscription below — no polling, no fan-out to maintain. */
+const BOOTSTRAP_FAN_OUT_CAP = 3;
+
+/** Cap on the rendered list. Bootstrap + every WS push prepends, the
+ *  list is sliced to this size after each update. Mirrors the prior
+ *  polling-loop behaviour. */
+const COMMS_RENDER_CAP = 20;
+
 /**
  * Overlay showing recent A2A communications between workspaces.
- * Renders as a floating log panel that auto-updates.
+ *
+ * Update shape (issue #61 Stage 1, replaces the 30s polling loop):
+ *  - On mount (when visible): one HTTP bootstrap per online workspace,
+ *    capped at BOOTSTRAP_FAN_OUT_CAP. Yields the initial recent-comms
+ *    window without waiting for live events.
+ *  - Steady state: subscribes to ACTIVITY_LOGGED via useSocketEvent.
+ *    Each event with a matching activity_type from a visible online
+ *    workspace gets synthesised into a Communication and prepended.
+ *  - Visibility re-open: re-bootstraps so the user sees the freshest
+ *    window even if WS was idle while collapsed.
+ *
+ * No interval poll. The singleton ReconnectingSocket in `store/socket.ts`
+ * already owns reconnect/backoff/health-check, and `useSocketEvent`
+ * inherits those guarantees. If WS is genuinely unhealthy, the overlay
+ * shows the bootstrap snapshot until the next visibility re-open or
+ * the next WS reconnect (which fires its own rehydrate burst).
  */
 export function CommunicationOverlay() {
   const [comms, setComms] = useState<Communication[]>([]);
   const [visible, setVisible] = useState(true);
   const selectedNodeId = useCanvasStore((s) => s.selectedNodeId);
   const nodes = useCanvasStore((s) => s.nodes);
+  // nodesRef gives the WS handler current node-name resolution without
+  // re-subscribing on every node-list change. The bus listener is
+  // registered exactly once per mount; subscriber-side filtering reads
+  // the latest value via this ref.
   const nodesRef = useRef(nodes);
   nodesRef.current = nodes;
 
-  const fetchComms = useCallback(async () => {
+  const bootstrapComms = useCallback(async () => {
     try {
-      // Fan-out cap: each polled workspace = 1 round-trip. The platform
-      // rate limits at 600 req/min/IP; combined with heartbeats + other
-      // canvas polling, every workspace polled here costs ~6 req/min
-      // (1 every 30s × 1 per workspace). Capping at 3 keeps this
-      // overlay's footprint at 18 req/min worst case — well under
-      // budget even with 8+ workspaces visible. Caught 2026-05-04 when
-      // a user with 8+ workspaces (Design Director + 6 sub-agents +
-      // 3 standalones) saw sustained 429s in canvas console.
       const onlineNodes = nodesRef.current.filter((n) => n.data.status === "online");
       const allComms: Communication[] = [];
 
-      for (const node of onlineNodes.slice(0, 3)) {
+      for (const node of onlineNodes.slice(0, BOOTSTRAP_FAN_OUT_CAP)) {
         try {
           const activities = await api.get<Array<{
             id: string;
@@ -59,8 +99,8 @@ export function CommunicationOverlay() {
 
           for (const a of activities) {
             if (a.activity_type === "a2a_send" || a.activity_type === "a2a_receive") {
-              const sourceNode = nodes.find((n) => n.id === (a.source_id || a.workspace_id));
-              const targetNode = nodes.find((n) => n.id === (a.target_id || ""));
+              const sourceNode = nodesRef.current.find((n) => n.id === (a.source_id || a.workspace_id));
+              const targetNode = nodesRef.current.find((n) => n.id === (a.target_id || ""));
               allComms.push({
                 id: a.id,
                 sourceId: a.source_id || a.workspace_id,
@@ -76,11 +116,12 @@ export function CommunicationOverlay() {
             }
           }
         } catch {
-          // Skip workspaces that fail
+          // Per-workspace failures must not blank the panel — the same
+          // robustness the polling version had.
         }
       }
 
-      // Sort by timestamp, newest first, dedupe
+      // Newest-first with id-dedup, capped at COMMS_RENDER_CAP.
       const seen = new Set<string>();
       const sorted = allComms
         .sort((a, b) => b.timestamp.localeCompare(a.timestamp))
@@ -89,29 +130,78 @@ export function CommunicationOverlay() {
           seen.add(c.id);
           return true;
         })
-        .slice(0, 20);
+        .slice(0, COMMS_RENDER_CAP);
 
       setComms(sorted);
     } catch {
-      // Silently handle API errors
+      // Bootstrap failure is non-blocking — the WS subscription below
+      // will populate the panel as live events arrive.
     }
   }, []);
 
+  // Bootstrap once on mount + every time the user re-opens after a
+  // collapse. Closed-panel state intentionally drops live updates so
+  // the panel doesn't churn invisible state — the next open reloads.
   useEffect(() => {
-    // Gate polling on visibility — when the user collapses the overlay
-    // the data isn't being read, so the per-workspace fan-out becomes
-    // pure rate-limit overhead. Pre-fix this overlay polled regardless
-    // of whether the panel was shown, costing ~36 req/min from a
-    // hidden surface.
     if (!visible) return;
-    fetchComms();
-    // 30s cadence (was 10s). At 3-workspace fan-out that's 6 req/min
-    // worst case from this overlay. Combined with heartbeats (~30/min)
-    // and other canvas polling, leaves ample headroom under the 600/
-    // min/IP server-side rate limit even at 8+ workspace tenants.
-    const interval = setInterval(fetchComms, 30000);
-    return () => clearInterval(interval);
-  }, [fetchComms, visible]);
+    bootstrapComms();
+  }, [bootstrapComms, visible]);
+
+  // Live-update path. Filters server-side ACTIVITY_LOGGED events down
+  // to the comm-overlay-relevant subset and prepends each into the
+  // rendered list with the same dedup the bootstrap path uses.
+  //
+  // Scope guard: ignore events for workspaces not in the visible online
+  // set, so a user collapsing one workspace doesn't see its comms
+  // continue to scroll in. Same shape the bootstrap path applies.
+  useSocketEvent((msg) => {
+    if (!visible) return;
+    if (msg.event !== "ACTIVITY_LOGGED") return;
+
+    const p = (msg.payload || {}) as ActivityLoggedPayload;
+    const type = p.activity_type;
+    if (type !== "a2a_send" && type !== "a2a_receive" && type !== "task_update") return;
+
+    const wsId = msg.workspace_id;
+    const onlineSet = new Set(
+      nodesRef.current.filter((n) => n.data.status === "online").map((n) => n.id),
+    );
+    if (!onlineSet.has(wsId)) return;
+
+    const sourceId = p.source_id || wsId;
+    const targetId = p.target_id || "";
+    const sourceNode = nodesRef.current.find((n) => n.id === sourceId);
+    const targetNode = nodesRef.current.find((n) => n.id === targetId);
+
+    const incoming: Communication = {
+      id: p.id || `${msg.timestamp || Date.now()}:${sourceId}:${targetId}`,
+      sourceId,
+      targetId,
+      sourceName: sourceNode?.data.name || "Unknown",
+      targetName: targetNode?.data.name || "Unknown",
+      type: type as Communication["type"],
+      summary: p.summary || "",
+      status: p.status || "ok",
+      timestamp: p.created_at || msg.timestamp || new Date().toISOString(),
+      durationMs: p.duration_ms ?? null,
+    };
+
+    setComms((prev) => {
+      // Prepend, dedup by id, re-cap. Functional setState is necessary
+      // because two ACTIVITY_LOGGED events arriving in the same React
+      // batch would otherwise read a stale `comms` from the closure.
+      const seen = new Set<string>();
+      const merged = [incoming, ...prev]
+        .sort((a, b) => b.timestamp.localeCompare(a.timestamp))
+        .filter((c) => {
+          if (seen.has(c.id)) return false;
+          seen.add(c.id);
+          return true;
+        })
+        .slice(0, COMMS_RENDER_CAP);
+      return merged;
+    });
+  });
 
   if (!visible || comms.length === 0) {
     return (
diff --git a/canvas/src/components/__tests__/A2ATopologyOverlay.test.tsx b/canvas/src/components/__tests__/A2ATopologyOverlay.test.tsx
index 6cdd19a7..ab470e18 100644
--- a/canvas/src/components/__tests__/A2ATopologyOverlay.test.tsx
+++ b/canvas/src/components/__tests__/A2ATopologyOverlay.test.tsx
@@ -41,6 +41,10 @@ vi.mock("@/store/canvas", () => ({
 // ── Imports (after mocks) ─────────────────────────────────────────────────────
 
 import { api } from "@/lib/api";
+import {
+  emitSocketEvent,
+  _resetSocketEventListenersForTests,
+} from "@/store/socket-events";
 import {
   buildA2AEdges,
   formatA2ARelativeTime,
@@ -342,6 +346,151 @@ describe("A2ATopologyOverlay component", () => {
     expect(mockGet.mock.calls.length).toBe(callsAfterMount);
   });
 
+  // ── #61 Stage 2: ACTIVITY_LOGGED subscription tests ────────────────────────
+  //
+  // Pin the post-#61 behaviour: WS push for delegation contributes to
+  // the overlay's edge buffer with NO additional HTTP fetch. Same shape
+  // as Stage 1 (CommunicationOverlay).
+
+  describe("#61 stage 2 — ACTIVITY_LOGGED subscription", () => {
+    beforeEach(() => {
+      _resetSocketEventListenersForTests();
+    });
+    afterEach(() => {
+      _resetSocketEventListenersForTests();
+    });
+
+    function emitDelegation(overrides: {
+      workspaceId?: string;
+      sourceId?: string;
+      targetId?: string;
+      method?: string;
+      activityType?: string;
+    } = {}) {
+      // Use Date.now() (real time, fake-timer-frozen) rather than the
+      // hardcoded NOW constant — buildA2AEdges prunes by Date.now() -
+      // A2A_WINDOW_MS, so a row dated against the wrong epoch silently
+      // falls outside the window and the test fails for a confusing
+      // reason ("edges array empty" vs "filter dropped my row").
+      const realNow = Date.now();
+      emitSocketEvent({
+        event: "ACTIVITY_LOGGED",
+        workspace_id: overrides.workspaceId ?? "ws-a",
+        timestamp: new Date(realNow).toISOString(),
+        payload: {
+          id: `act-${Math.random().toString(36).slice(2)}`,
+          activity_type: overrides.activityType ?? "delegation",
+          method: overrides.method ?? "delegate",
+          source_id: overrides.sourceId ?? "ws-a",
+          target_id: overrides.targetId ?? "ws-b",
+          status: "ok",
+          created_at: new Date(realNow - 30_000).toISOString(),
+        },
+      });
+    }
+
+    it("does NOT poll on a 60s interval after bootstrap (post-#61)", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      await act(async () => { await Promise.resolve(); });
+      const callsAfterBootstrap = mockGet.mock.calls.length;
+      expect(callsAfterBootstrap).toBe(2); // ws-a + ws-b
+
+      // Pre-#61: a 60s clock tick would fire a fresh fan-out (2 more
+      // calls). Post-#61: no interval, no extra calls.
+      await act(async () => {
+        vi.advanceTimersByTime(120_000);
+      });
+      expect(mockGet.mock.calls.length).toBe(callsAfterBootstrap);
+    });
+
+    it("WS push for a delegation event from a visible workspace updates edges with NO HTTP call", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      await act(async () => { await Promise.resolve(); await Promise.resolve(); });
+      mockGet.mockClear();
+      mockStoreState.setA2AEdges.mockClear();
+
+      await act(async () => {
+        emitDelegation({ sourceId: "ws-a", targetId: "ws-b" });
+      });
+
+      // Edges-set called with at least one a2a edge for the new push.
+      const calls = mockStoreState.setA2AEdges.mock.calls;
+      expect(calls.length).toBeGreaterThanOrEqual(1);
+      const lastCall = calls[calls.length - 1][0] as Array<{ id: string }>;
+      expect(lastCall.some((e) => e.id === "a2a-ws-a-ws-b")).toBe(true);
+
+      // Critical: no HTTP fetch fired during the WS path.
+      expect(mockGet).not.toHaveBeenCalled();
+    });
+
+    it("WS push for a non-delegation activity_type is ignored", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      await act(async () => { await Promise.resolve(); });
+      mockStoreState.setA2AEdges.mockClear();
+
+      await act(async () => {
+        emitDelegation({ activityType: "a2a_send" });
+      });
+
+      // setA2AEdges must not be called by the WS handler — the only
+      // setA2AEdges calls in this test came from the initial bootstrap.
+      expect(mockStoreState.setA2AEdges).not.toHaveBeenCalled();
+    });
+
+    it("WS push for a delegate_result row is ignored (mirrors buildA2AEdges filter)", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      await act(async () => { await Promise.resolve(); });
+      mockStoreState.setA2AEdges.mockClear();
+
+      await act(async () => {
+        emitDelegation({ method: "delegate_result" });
+      });
+
+      // delegate_result rows do not contribute to the edge count — they
+      // are completion signals, not initiations.
+      expect(mockStoreState.setA2AEdges).not.toHaveBeenCalled();
+    });
+
+    it("WS push from a hidden workspace is ignored", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      await act(async () => { await Promise.resolve(); });
+      mockStoreState.setA2AEdges.mockClear();
+
+      await act(async () => {
+        emitDelegation({ workspaceId: "ws-hidden" });
+      });
+
+      expect(mockStoreState.setA2AEdges).not.toHaveBeenCalled();
+    });
+
+    it("WS push while showA2AEdges is false is ignored", async () => {
+      mockStoreState.showA2AEdges = false;
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      mockGet.mockResolvedValue([] as any);
+      render(<A2ATopologyOverlay />);
+      // The mount path with showA2AEdges=false calls setA2AEdges([])
+      // once — clear that to isolate the WS path.
+      mockStoreState.setA2AEdges.mockClear();
+
+      await act(async () => {
+        emitDelegation();
+      });
+
+      expect(mockStoreState.setA2AEdges).not.toHaveBeenCalled();
+      expect(mockGet).not.toHaveBeenCalled();
+    });
+  });
+
   it("re-fetches when the visible ID set actually changes", async () => {
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     mockGet.mockResolvedValue([] as any);
diff --git a/canvas/src/components/__tests__/CommunicationOverlay.test.tsx b/canvas/src/components/__tests__/CommunicationOverlay.test.tsx
index 3bed0076..c15249a2 100644
--- a/canvas/src/components/__tests__/CommunicationOverlay.test.tsx
+++ b/canvas/src/components/__tests__/CommunicationOverlay.test.tsx
@@ -1,18 +1,28 @@
 // @vitest-environment jsdom
 /**
- * CommunicationOverlay tests — pin the rate-limit fix shipped 2026-05-04.
+ * CommunicationOverlay tests — pin both the 2026-05-04 fan-out cap fix
+ * AND the 2026-05-07 polling → ACTIVITY_LOGGED-subscriber refactor
+ * (issue #61 stage 1).
  *
- * The overlay polls /workspaces/:id/activity?limit=5 for each online
- * workspace. Pre-fix it (a) polled regardless of visibility and (b)
- * fanned out to 6 workspaces every 10s. With 8+ workspaces a user
- * triggered sustained 429s (server-side rate limit is 600 req/min/IP).
+ * The overlay used to poll /workspaces/:id/activity?limit=5 on a 30s
+ * interval per online workspace (capped at 3). Post-#61: it bootstraps
+ * once on mount via the same HTTP path (cap of 3 retained), then
+ * subscribes to ACTIVITY_LOGGED via the global socket bus for live
+ * updates. No interval poll.
  *
  * These tests pin:
- *  1. Fan-out cap of 3 — even with 6 online nodes, only 3 fetches
- *  2. Visibility gate — when collapsed, no polling
+ *  1. Bootstrap fan-out cap of 3 — even with 6 online nodes, only 3
+ *     HTTP fetches on mount.
+ *  2. Visibility gate — when collapsed, no HTTP fetches; re-open
+ *     re-bootstraps.
+ *  3. NO interval polling — advancing the clock past 30s does not fire
+ *     additional HTTP calls.
+ *  4. WS push extends the rendered list without firing any HTTP call.
+ *  5. WS push for an offline workspace is ignored.
+ *  6. WS push for a non-comm activity_type is ignored.
  *
- * If a future refactor pushes either dial back up, CI fails before
- * the regression hits a paying tenant.
+ * If a future refactor regresses any of these, CI fails before the
+ * regression hits a paying tenant.
  */
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import { render, cleanup, act, fireEvent } from "@testing-library/react";
@@ -23,7 +33,7 @@ vi.mock("@/lib/api", () => ({
   api: { get: vi.fn() },
 }));
 
-// Six online nodes — enough to verify the cap of 3.
+// Six online nodes — enough to verify the bootstrap cap of 3.
 const mockStoreState = {
   selectedNodeId: null as string | null,
   nodes: [
@@ -56,6 +66,10 @@ vi.mock("@/lib/design-tokens", () => ({
 // ── Imports (after mocks) ─────────────────────────────────────────────────────
 
 import { api } from "@/lib/api";
+import {
+  emitSocketEvent,
+  _resetSocketEventListenersForTests,
+} from "@/store/socket-events";
 import { CommunicationOverlay } from "../CommunicationOverlay";
 
 const mockGet = vi.mocked(api.get);
@@ -66,30 +80,34 @@ beforeEach(() => {
   vi.useFakeTimers();
   mockGet.mockReset();
   mockGet.mockResolvedValue([]);
+  // Drop any subscribers the previous test left on the singleton bus —
+  // each render adds one via useSocketEvent.
+  _resetSocketEventListenersForTests();
 });
 
 afterEach(() => {
   cleanup();
   vi.useRealTimers();
+  _resetSocketEventListenersForTests();
 });
 
 // ── Tests ─────────────────────────────────────────────────────────────────────
 
-describe("CommunicationOverlay — fan-out cap", () => {
-  it("polls at most 3 of 6 online workspaces (rate-limit floor)", async () => {
+describe("CommunicationOverlay — bootstrap fan-out cap", () => {
+  it("bootstraps at most 3 of 6 online workspaces (rate-limit floor preserved post-#61)", async () => {
     await act(async () => {
       render(<CommunicationOverlay />);
     });
-    // Mount fires the first poll synchronously (no interval tick yet).
-    // Pre-fix: 6 calls. Post-fix: 3.
+    // Mount fires the bootstrap synchronously — pre-#61 this was the
+    // first poll cycle; post-#61 it's the only HTTP fetch (live updates
+    // arrive via WS push). 6 nodes → 3 fetches.
     expect(mockGet).toHaveBeenCalledTimes(3);
-    // Verify the calls are for the FIRST 3 online nodes (slice order).
     expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-1/activity?limit=5");
     expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-2/activity?limit=5");
     expect(mockGet).toHaveBeenCalledWith("/workspaces/ws-3/activity?limit=5");
   });
 
-  it("never polls offline workspaces", async () => {
+  it("never bootstraps offline workspaces", async () => {
     await act(async () => {
       render(<CommunicationOverlay />);
     });
@@ -99,40 +117,39 @@ describe("CommunicationOverlay — fan-out cap", () => {
   });
 });
 
-describe("CommunicationOverlay — cadence", () => {
-  it("uses 30s interval cadence (was 10s pre-fix)", async () => {
+describe("CommunicationOverlay — no interval polling (post-#61)", () => {
+  // The pre-#61 implementation re-fetched every 30s per workspace.
+  // Post-#61 the only HTTP path is the bootstrap on mount + on
+  // visibility-toggle. This test pins the absence of any interval
+  // poll: a 60s clock advance must not produce a second round of
+  // fetches.
+  it("does NOT poll on a 30s interval after bootstrap", async () => {
     await act(async () => {
       render(<CommunicationOverlay />);
     });
-    expect(mockGet).toHaveBeenCalledTimes(3); // initial mount poll
+    expect(mockGet).toHaveBeenCalledTimes(3); // initial bootstrap
+    mockGet.mockClear();
 
-    // Advance 10s — pre-fix this would fire another poll. Post-fix: silent.
+    // Advance 60s — well past any plausible cadence the prior version
+    // could have used.
     await act(async () => {
-      vi.advanceTimersByTime(10_000);
+      vi.advanceTimersByTime(60_000);
     });
-    expect(mockGet).toHaveBeenCalledTimes(3);
-
-    // Advance to 30s — interval fires.
-    await act(async () => {
-      vi.advanceTimersByTime(20_000);
-    });
-    expect(mockGet).toHaveBeenCalledTimes(6); // +3 from second tick
+    expect(mockGet).not.toHaveBeenCalled();
   });
 });
 
 describe("CommunicationOverlay — visibility gate", () => {
-  // The visibility gate is the dial that drops collapsed-panel polling
-  // to ZERO. The cadence test above can't catch its removal — if a
-  // refactor dropped `if (!visible) return`, the cadence test would
-  // still pass because the effect would still fire every 30s.
+  // The visibility gate now does two things post-#61:
+  //   - while closed, the WS handler short-circuits (no setComms churn)
+  //   - re-opening triggers a fresh bootstrap so the list reflects
+  //     anything that happened while the panel was collapsed
   //
   // Direct probe: render with comms-returning mock so the panel
   // actually renders (close button only exists in the expanded panel,
   // not the collapsed button-state). Click close, advance the clock,
   // assert no further fetches.
-  it("stops polling after the user collapses the panel", async () => {
-    // Mock returns one a2a_send so comms.length > 0 → panel renders →
-    // close button accessible.
+  it("stops fetching while collapsed and re-bootstraps on re-open", async () => {
     mockGet.mockResolvedValue([
       {
         id: "act-1",
@@ -150,29 +167,202 @@ describe("CommunicationOverlay — visibility gate", () => {
     const { getByLabelText } = await act(async () => {
       return render(<CommunicationOverlay />);
     });
-    // Drain pending microtasks (resolves the await in fetchComms) so
-    // setComms lands and the panel renders. Don't advance time — that
-    // would fire the next interval tick and pollute the assertion.
+    // Drain pending microtasks (resolves the await in bootstrap) so
+    // setComms lands and the panel renders. Don't advance time — it's
+    // not load-bearing for the gate test, but matches the pattern used
+    // pre-#61 for stability.
     await act(async () => {
       await Promise.resolve();
       await Promise.resolve();
       await Promise.resolve();
     });
-    // Initial mount polled 3 workspaces.
-    expect(mockGet).toHaveBeenCalledTimes(3);
+    expect(mockGet).toHaveBeenCalledTimes(3); // initial bootstrap
     mockGet.mockClear();
 
-    // Click the close button. Synchronous getByLabelText avoids
-    // findBy's internal setTimeout (deadlocks under useFakeTimers).
+    // Click close. While closed, no fetches and no WS-driven updates.
+    const closeBtn = getByLabelText("Close communications panel");
+    await act(async () => {
+      fireEvent.click(closeBtn);
+    });
+    await act(async () => {
+      vi.advanceTimersByTime(60_000);
+    });
+    expect(mockGet).not.toHaveBeenCalled();
+
+    // Re-open via the collapsed button. Must trigger a fresh bootstrap.
+    const openBtn = getByLabelText("Show communications panel");
+    await act(async () => {
+      fireEvent.click(openBtn);
+    });
+    await act(async () => {
+      await Promise.resolve();
+      await Promise.resolve();
+    });
+    expect(mockGet).toHaveBeenCalledTimes(3); // re-bootstrap on re-open
+  });
+});
+
+describe("CommunicationOverlay — WS subscription (#61 stage 1 core)", () => {
+  // The load-bearing post-#61 behaviour. Every test in this block must
+  // verify (a) the WS push DID update the rendered comms list, and
+  // (b) NO additional HTTP call was fired — the whole point of the
+  // refactor is to remove the polling-driven HTTP traffic.
+  function emitActivityLogged(overrides: Partial<{
+    workspaceId: string;
+    payload: Record<string, unknown>;
+  }> = {}) {
+    emitSocketEvent({
+      event: "ACTIVITY_LOGGED",
+      workspace_id: overrides.workspaceId ?? "ws-1",
+      timestamp: new Date().toISOString(),
+      payload: {
+        id: `act-${Math.random().toString(36).slice(2)}`,
+        activity_type: "a2a_send",
+        source_id: "ws-1",
+        target_id: "ws-2",
+        summary: "live push",
+        status: "ok",
+        duration_ms: 42,
+        created_at: new Date().toISOString(),
+        ...overrides.payload,
+      },
+    });
+  }
+
+  it("WS push for a comm activity_type extends the rendered list with NO additional HTTP call", async () => {
+    const { container } = await act(async () => {
+      return render(<CommunicationOverlay />);
+    });
+    expect(mockGet).toHaveBeenCalledTimes(3); // bootstrap
+    mockGet.mockClear();
+
+    await act(async () => {
+      emitActivityLogged({ payload: { summary: "hello" } });
+    });
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    // Two pins:
+    //   1. comms list reflects the live push (look for the summary text)
+    //   2. zero HTTP fetches fired during the WS path
+    expect(container.textContent).toContain("hello");
+    expect(mockGet).not.toHaveBeenCalled();
+  });
+
+  it("WS push for an offline workspace is ignored", async () => {
+    const { container } = await act(async () => {
+      return render(<CommunicationOverlay />);
+    });
+    mockGet.mockClear();
+
+    await act(async () => {
+      emitActivityLogged({
+        workspaceId: "ws-offline",
+        payload: { source_id: "ws-offline", summary: "should-not-render" },
+      });
+    });
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(container.textContent).not.toContain("should-not-render");
+    expect(mockGet).not.toHaveBeenCalled();
+  });
+
+  it("WS push for a non-comm activity_type is ignored (e.g. delegation)", async () => {
+    const { container } = await act(async () => {
+      return render(<CommunicationOverlay />);
+    });
+    mockGet.mockClear();
+
+    await act(async () => {
+      emitActivityLogged({
+        payload: {
+          activity_type: "delegation",
+          summary: "should-not-render-delegation",
+        },
+      });
+    });
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(container.textContent).not.toContain("should-not-render-delegation");
+    expect(mockGet).not.toHaveBeenCalled();
+  });
+
+  it("WS push while the panel is collapsed is ignored (no churn on hidden state)", async () => {
+    // Bootstrap with one comm so the panel renders → close button
+    // accessible. Then collapse, emit a WS push, re-open: the rendered
+    // list must come from the re-bootstrap, NOT from the WS-push that
+    // arrived during the closed state. Also: nothing visible while
+    // closed (the collapsed button shows only the count, not summaries).
+    mockGet.mockResolvedValue([
+      {
+        id: "act-bootstrap",
+        workspace_id: "ws-1",
+        activity_type: "a2a_send",
+        source_id: "ws-1",
+        target_id: "ws-2",
+        summary: "bootstrap-summary",
+        status: "ok",
+        duration_ms: 1,
+        created_at: new Date().toISOString(),
+      },
+    ]);
+    const { getByLabelText, container } = await act(async () => {
+      return render(<CommunicationOverlay />);
+    });
+    await act(async () => {
+      await Promise.resolve();
+      await Promise.resolve();
+    });
+
+    // Collapse.
     const closeBtn = getByLabelText("Close communications panel");
     await act(async () => {
       fireEvent.click(closeBtn);
     });
 
-    // Advance well past the 30s cadence — gate should suppress the tick.
+    // Bootstrap mock returns nothing on the re-open path so we can
+    // distinguish "WS push leaked through the gate" from "re-bootstrap
+    // refilled the list."
+    mockGet.mockReset();
+    mockGet.mockResolvedValue([]);
+
     await act(async () => {
-      vi.advanceTimersByTime(60_000);
+      emitActivityLogged({
+        payload: { summary: "leaked-while-closed" },
+      });
     });
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    // Closed state: rendered DOM must not show any push-derived text.
+    expect(container.textContent).not.toContain("leaked-while-closed");
+  });
+
+  it("non-ACTIVITY_LOGGED events are ignored (e.g. WORKSPACE_OFFLINE)", async () => {
+    const { container } = await act(async () => {
+      return render(<CommunicationOverlay />);
+    });
+    mockGet.mockClear();
+
+    await act(async () => {
+      emitSocketEvent({
+        event: "WORKSPACE_OFFLINE",
+        workspace_id: "ws-1",
+        timestamp: new Date().toISOString(),
+        payload: { summary: "should-not-render-event" },
+      });
+    });
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(container.textContent).not.toContain("should-not-render-event");
     expect(mockGet).not.toHaveBeenCalled();
   });
 });
diff --git a/docs/engineering/ratelimit-observability.md b/docs/engineering/ratelimit-observability.md
new file mode 100644
index 00000000..9e886137
--- /dev/null
+++ b/docs/engineering/ratelimit-observability.md
@@ -0,0 +1,147 @@
+# Rate-limit observability runbook
+
+> Companion to issue #64 ("RATE_LIMIT default re-tune analysis"). After
+> #60 deployed the per-tenant `keyFor` keying, the right RATE_LIMIT
+> default became data-dependent. This runbook documents the metrics +
+> queries an operator should run to confirm whether the current 600
+> req/min/key default is correct, too tight, or too loose.
+
+## What's already exposed
+
+The workspace-server's existing Prometheus middleware
+(`workspace-server/internal/metrics/metrics.go`) tracks every request
+on every path:
+
+```
+molecule_http_requests_total{method, path, status}      counter
+molecule_http_request_duration_seconds_total{method,path,status}  counter
+```
+
+Path is the matched route pattern (`/workspaces/:id/activity` etc), so
+high-cardinality workspace UUIDs do not explode the label space.
+
+The rate limiter middleware (#60, `workspace-server/internal/middleware/ratelimit.go`)
+also stamps every response with `X-RateLimit-Limit`, `X-RateLimit-Remaining`,
+and `X-RateLimit-Reset`. Operators with browser-side or proxy-side
+header capture can read per-request bucket state directly.
+
+No new instrumentation is needed for #64's acceptance criteria. The
+metric surface is sufficient — this runbook just collects the queries.
+
+## Queries to run after #60 deploys
+
+### 1. Is the bucket actually firing 429s?
+
+```promql
+sum(rate(molecule_http_requests_total{status="429"}[5m]))
+```
+
+If this is zero on a given tenant, the bucket isn't being hit. If it's
+sustained > 1/min, dig in.
+
+### 2. Which routes attract 429s?
+
+```promql
+topk(
+  10,
+  sum by (path) (
+    rate(molecule_http_requests_total{status="429"}[5m])
+  )
+)
+```
+
+Expected shape post-#60:
+- `/workspaces/:id/activity` should be near zero — the canvas no longer
+  polls it on a 30s/60s/5s cadence (PRs #69 / #71 / #76).
+- Probe / health / heartbeat paths should be ~0 (those routes have a
+  separate IP-fallback bucket).
+
+If `/workspaces/:id/activity` 429s persist post-PRs-69/71/76 deploy, the
+canvas isn't running the WS-subscriber path — investigate WS health
+on that tenant.
+
+### 3. Per-bucket-key inference (no direct exposure today)
+
+The bucket map itself is in-memory only; we deliberately do **not**
+expose `org:<uuid>` ↔ remaining-tokens because that map can include
+SHA-256 hashes of bearer tokens. A tenant that wants per-key visibility
+should rely on response headers (`X-RateLimit-Remaining` on every
+response from a given session is the bucket's view of that session).
+
+If you genuinely need server-side per-bucket counts for triage,
+file a follow-up — the proper shape is a `/internal/ratelimit-stats`
+endpoint that emits **counts per key prefix only** (e.g. `org:`, `tok:`,
+`ip:`), never the key payloads. Don't roll that ad-hoc; it's a security
+review surface.
+
+## Decision tree for the re-tune
+
+After 14 days of production traffic on a tenant, look at the queries
+above and walk this tree:
+
+```
+Q1: Is the 429 rate sustained > 0.1/sec on any tenant?
+  ├─ NO  → The 600 default has comfortable headroom. Either keep it,
+  │        or lower it carefully (300) ONLY if you have a documented
+  │        reason (e.g. a misbehaving client we want to throttle harder).
+  │        Default to "no change" — see #64 for the math.
+  └─ YES → Q2.
+
+Q2: Is the 429 rate concentrated on ONE tenant or spread across many?
+  ├─ ONE tenant → Operator override: set RATE_LIMIT=1200 or 1800 on that
+  │               tenant's box. Document in the tenant's ops note. The
+  │               default does not need to change.
+  └─ MANY tenants → Q3.
+
+Q3: Are the 429s on a route that polls (e.g. /activity / /peers)?
+  ├─ YES → Confirm PRs #69, #71, #76 have actually deployed to those
+  │         tenants. If they have and 429s persist, the canvas may have
+  │         a regression — do not raise RATE_LIMIT. File a canvas issue.
+  └─ NO  → 429s on mutating routes mean genuine load. Raise the default
+            to 1200 in `workspace-server/internal/router/router.go:54`.
+            Same PR should attach: the metric chart, the time window,
+            and a paragraph explaining what changed in our traffic shape.
+```
+
+## Alert rule template (drop-in for Prometheus)
+
+```yaml
+# Sustained 429s — file is the SLO trip-wire. If this fires, walk the
+# decision tree above. NB: the issue#64 acceptance criterion is "two
+# weeks of metrics"; this alert is the inverse — it tells you something
+# changed before the two weeks are up.
+groups:
+  - name: workspace-server-ratelimit
+    rules:
+      - alert: WorkspaceServerRateLimit429Sustained
+        expr: |
+          sum by (instance) (
+            rate(molecule_http_requests_total{status="429"}[10m])
+          ) > 0.1
+        for: 30m
+        labels:
+          severity: warning
+          owner: workspace-server
+        annotations:
+          summary: "{{ $labels.instance }} sustained 429s — see ratelimit-observability runbook"
+          runbook: "https://git.moleculesai.app/molecule-ai/molecule-core/blob/main/docs/engineering/ratelimit-observability.md"
+```
+
+Threshold rationale: 0.1 req/s = 6/min sustained over 10min. Below
+that, a 429 is almost certainly a transient burst that the canvas's
+retry-once handler at `canvas/src/lib/api.ts:55` already absorbs. The
+30m `for:` keeps the alert from chattering on a brief blip.
+
+## Companion probe script
+
+For one-off triage when an operator can reproduce the problem in their
+own browser, `scripts/edge-429-probe.sh` (#62) reproduces a canvas-
+sized burst against a tenant subdomain and dumps each 429's response
+shape so the operator can distinguish workspace-server bucket overflow
+from CF/Vercel edge rate-limiting without dashboard access.
+
+```sh
+./scripts/edge-429-probe.sh hongming.moleculesai.app --burst 80 --out /tmp/edge.txt
+```
+
+The script's report header explains how to read the output.
diff --git a/scripts/edge-429-probe.sh b/scripts/edge-429-probe.sh
new file mode 100755
index 00000000..a7db80c2
--- /dev/null
+++ b/scripts/edge-429-probe.sh
@@ -0,0 +1,155 @@
+#!/usr/bin/env bash
+# edge-429-probe.sh — capture 429 origin (workspace-server vs CF/Vercel edge)
+# during a simulated canvas-burst against a tenant subdomain.
+#
+# Issue molecule-core#62. The post-#60 verification step asks an
+# operator with CF/Vercel dashboard access to confirm whether the
+# layout-chunk 429s observed in DevTools were:
+#   (a) workspace-server bucket overflow (closes once #60 deploys), or
+#   (b) actual edge-layer rate-limiting (CF or Vercel).
+#
+# This script doesn't need dashboard access. It reproduces the burst
+# pattern locally and dumps every 429's response shape so the operator
+# can distinguish (a) from (b) by inspection: workspace-server emits a
+# JSON body, CF emits HTML, Vercel emits a different HTML. Headers tell
+# the same story (cf-ray vs x-vercel-*).
+#
+# Usage:
+#   ./scripts/edge-429-probe.sh <tenant-host> [--burst N] [--waves N] [--pause SECS] [--out file]
+#
+# Example:
+#   ./scripts/edge-429-probe.sh hongming.moleculesai.app --burst 80 --out /tmp/edge.txt
+#
+# The script is read-only against the target — it only issues GETs to
+# public-by-design endpoints. No mutating requests, no credential use.
+
+set -euo pipefail
+
+# ── Help / usage handling first, before positional capture ────────────────────
+case "${1:-}" in
+  -h|--help|"")
+    sed -n '/^# edge-429-probe.sh/,/^$/p' "$0" | sed 's/^# \{0,1\}//'
+    exit 0
+    ;;
+esac
+
+HOST="$1"; shift
+BURST=80
+WAVES=3
+WAVE_PAUSE=2
+OUT=""
+
+while [ "${1:-}" != "" ]; do
+  case "$1" in
+    --burst) BURST="$2"; shift 2 ;;
+    --waves) WAVES="$2"; shift 2 ;;
+    --pause) WAVE_PAUSE="$2"; shift 2 ;;
+    --out)   OUT="$2";   shift 2 ;;
+    -h|--help)
+      sed -n '/^# edge-429-probe.sh/,/^$/p' "$0" | sed 's/^# \{0,1\}//'
+      exit 0
+      ;;
+    *) echo "unknown arg: $1" >&2; exit 2 ;;
+  esac
+done
+
+# ── Endpoint discovery ────────────────────────────────────────────────────────
+echo "→ Discovering a layout-chunk URL from canvas root..." >&2
+ROOT_BODY=$(curl -fsSL --max-time 10 "https://${HOST}/" 2>/dev/null || true)
+LAYOUT_PATH=$(echo "$ROOT_BODY" \
+  | grep -oE '/_next/static/chunks/layout-[A-Za-z0-9_-]+\.js' \
+  | head -1 || true)
+if [ -z "$LAYOUT_PATH" ]; then
+  LAYOUT_PATH="/_next/static/chunks/layout-probe-not-found.js"
+  echo "  (no layout chunk discovered — using sentinel path; 404 on this is expected)" >&2
+else
+  echo "  layout chunk: $LAYOUT_PATH" >&2
+fi
+
+# Probe URL: a generic activity endpoint. The rate-limiter middleware
+# runs BEFORE workspace-id validation, so unauth/invalid-id requests
+# still hit the bucket.
+ACTIVITY_PATH="/workspaces/00000000-0000-0000-0000-000000000000/activity?probe=edge-429"
+
+# ── Fire one curl, write a single-line JSON-ish status record to stdout ──────
+# Inlined into xargs as a heredoc-style command rather than a function so
+# the function-export pitfalls (some shells lose `export -f` across xargs)
+# don't apply. Each output line is a parseable record; failed curls emit
+# a curl_err record so request volume is preserved.
+TMP_RESULTS="$(mktemp -t edge-429-probe.XXXXXX)"
+trap 'rm -f "$TMP_RESULTS"' EXIT
+
+run_burst() {
+  # $1 = path; $2 = label; $3 = wave_id
+  local path="$1" label="$2" wave="$3"
+  local i
+  for i in $(seq 1 "$BURST"); do
+    {
+      out=$(curl -sS --max-time 10 -o /dev/null \
+        -w 'status=%{http_code} size=%{size_download} time=%{time_total} server=%{header.server} cf_ray=%{header.cf-ray} x_vercel=%{header.x-vercel-id} retry_after=%{header.retry-after} content_type=%{header.content-type} x_ratelimit_limit=%{header.x-ratelimit-limit} x_ratelimit_remaining=%{header.x-ratelimit-remaining} x_ratelimit_reset=%{header.x-ratelimit-reset}\n' \
+        "https://${HOST}${path}" 2>/dev/null) || out="status=curl_err"
+      printf 'label=%s-%s-%s %s\n' "$label" "$wave" "$i" "$out" >> "$TMP_RESULTS"
+    } &
+  done
+  wait
+}
+
+emit() {
+  if [ -n "$OUT" ]; then
+    printf '%s\n' "$*" >> "$OUT"
+  else
+    printf '%s\n' "$*"
+  fi
+}
+
+if [ -n "$OUT" ]; then : > "$OUT"; fi
+
+emit "# edge-429-probe report"
+emit "# host=$HOST burst=$BURST waves=$WAVES pause=${WAVE_PAUSE}s"
+emit "# layout_path=$LAYOUT_PATH"
+emit "# activity_path=$ACTIVITY_PATH"
+emit "# generated=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+emit ""
+
+for wave in $(seq 1 "$WAVES"); do
+  emit "## wave $wave"
+  : > "$TMP_RESULTS"
+  run_burst "$LAYOUT_PATH" "layout" "$wave"
+  run_burst "$ACTIVITY_PATH" "activity" "$wave"
+  while read -r line; do
+    emit "  $line"
+  done < "$TMP_RESULTS"
+  if [ "$wave" -lt "$WAVES" ]; then
+    sleep "$WAVE_PAUSE"
+  fi
+done
+
+emit ""
+emit "## summary — how to read the report"
+emit "#   status=429 + content_type starts with application/json + x_ratelimit_limit set"
+emit "#     => workspace-server bucket overflow. Closes when #60 deploys."
+emit "#   status=429 + cf_ray set + content_type=text/html"
+emit "#     => Cloudflare WAF / rate-limit. Audit dashboard rules per #62."
+emit "#   status=429 + x_vercel set + content_type=text/html"
+emit "#     => Vercel edge / Bot Fight Mode. Audit Vercel project per #62."
+emit "#   status=429 with no server/cf_ray/x_vercel"
+emit "#     => corporate proxy or VPN. Not actionable in this repo."
+
+if [ -n "$OUT" ]; then
+  echo "→ Report written to $OUT" >&2
+  # Match only data lines (begin with two-space indent + "label="),
+  # not the summary's reference text which also mentions "status=429".
+  # grep -c outputs "0" + exits 1 when zero matches; `|| true` masks
+  # the exit status so set -e doesn't trip without losing the count.
+  total=$(grep -c '^  label=' "$OUT" 2>/dev/null || true)
+  total429=$(grep -c '^  label=.*status=429' "$OUT" 2>/dev/null || true)
+  total=${total:-0}
+  total429=${total429:-0}
+  echo "→ Totals: ${total429} of ${total} requests returned 429" >&2
+  if [ "${total429}" -gt 0 ]; then
+    echo "→ Per-label 429 counts:" >&2
+    grep '^  label=.*status=429' "$OUT" \
+      | sed -E 's/^  label=([^-]+).*/  \1/' \
+      | sort | uniq -c >&2
+  fi
+fi
diff --git a/workspace-server/internal/middleware/ratelimit.go b/workspace-server/internal/middleware/ratelimit.go
index 1b2f50dd..e01324d3 100644
--- a/workspace-server/internal/middleware/ratelimit.go
+++ b/workspace-server/internal/middleware/ratelimit.go
@@ -5,17 +5,19 @@ import (
 	"context"
 	"net/http"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
 	"github.com/gin-gonic/gin"
 )
 
-// RateLimiter implements a simple token bucket rate limiter per IP.
+// RateLimiter implements a token bucket rate limiter keyed by tenant
+// identity (org id, then bearer token, then client IP — see keyFor).
 type RateLimiter struct {
-	mu      sync.Mutex
-	buckets map[string]*bucket
-	rate    int           // tokens per interval
+	mu       sync.Mutex
+	buckets  map[string]*bucket
+	rate     int // tokens per interval
 	interval time.Duration
 }
 
@@ -42,9 +44,9 @@ func NewRateLimiter(rate int, interval time.Duration, ctx context.Context) *Rate
 			case <-ticker.C:
 				rl.mu.Lock()
 				cutoff := time.Now().Add(-10 * time.Minute)
-				for ip, b := range rl.buckets {
+				for k, b := range rl.buckets {
 					if b.lastReset.Before(cutoff) {
-						delete(rl.buckets, ip)
+						delete(rl.buckets, k)
 					}
 				}
 				rl.mu.Unlock()
@@ -54,29 +56,73 @@ func NewRateLimiter(rate int, interval time.Duration, ctx context.Context) *Rate
 	return rl
 }
 
-// Middleware returns a Gin middleware that rate limits by client IP.
+// keyFor returns the bucket identifier for this request. Priority:
+//
+//  1. X-Molecule-Org-Id header — when present (CP-routed SaaS traffic),
+//     isolates tenants from each other regardless of the upstream proxy IP
+//     they all share.
+//  2. SHA-256 of Authorization Bearer token — when present (per-workspace
+//     bearer, ADMIN_TOKEN, org-scoped API token). On a per-tenant Caddy
+//     box where the org-id header isn't attached, this still distinguishes
+//     distinct user sessions on the same egress IP.
+//  3. ClientIP() — anonymous probes, /health scrapes, registry boot
+//     signals (when SetTrustedProxies(nil) is in effect, this is the
+//     direct TCP RemoteAddr — fine for the probe surface, not fine as a
+//     primary key behind a proxy, hence the priority order above).
+//
+// Mixing these namespaces is fine because they never collide: org ids
+// are UUIDs ("org:..."), token hashes are 64-char hex ("tok:..."), IPs
+// contain dots/colons ("ip:...").
+//
+// Security note on X-Molecule-Org-Id spoofing: the rate limiter runs
+// BEFORE TenantGuard, so the org-id value here is unvalidated. A caller
+// reaching workspace-server directly could spoof the header to drain
+// another org's bucket. In production this surface is closed by the
+// CP/Caddy front: tenant SGs reject :8080 from the public internet, and
+// CP rewrites the header to the verified org. If a future deployment
+// exposes :8080 directly, validate the org-id (e.g. against
+// MOLECULE_ORG_ID) before keying on it, or move this middleware after
+// TenantGuard. The token-hash and IP fallbacks are unspoofable.
+//
+// Issue #59 — replaces the previous IP-only keying that silently
+// collapsed all canvas traffic into one bucket once #179 disabled
+// proxy-header trust. See the issue for the deployment-shape analysis.
+func (rl *RateLimiter) keyFor(c *gin.Context) string {
+	if orgID := strings.TrimSpace(c.GetHeader("X-Molecule-Org-Id")); orgID != "" {
+		return "org:" + orgID
+	}
+	if tok := bearerFromHeader(c.GetHeader("Authorization")); tok != "" {
+		return "tok:" + tokenKey(tok)
+	}
+	return "ip:" + c.ClientIP()
+}
+
+// Middleware returns a Gin middleware that rate limits per caller. The
+// caller-key derivation lives in keyFor — see that function's doc for
+// the priority list and rationale.
 func (rl *RateLimiter) Middleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
 		// Tier-1b dev-mode hatch — same gate as AdminAuth / WorkspaceAuth /
 		// discovery. On a local single-user Docker setup the 600-req/min
 		// bucket fills fast: a 15-workspace canvas + activity polling +
-		// approvals polling + A2A overlay + initial hydration all share
-		// one IP bucket, so a minute of active use can trip 429 and blank
-		// the page. Gated by MOLECULE_ENV=development + empty ADMIN_TOKEN
-		// so SaaS production keeps the bucket.
+		// approvals polling + A2A overlay + initial hydration all land in
+		// one bucket (whichever keyFor returns — typically the dev user's
+		// IP or shared admin token), so a minute of active use can trip
+		// 429 and blank the page. Gated by MOLECULE_ENV=development +
+		// empty ADMIN_TOKEN so SaaS production keeps the bucket.
 		if isDevModeFailOpen() {
 			c.Header("X-RateLimit-Limit", "unlimited")
 			c.Next()
 			return
 		}
 
-		ip := c.ClientIP()
+		key := rl.keyFor(c)
 
 		rl.mu.Lock()
-		b, exists := rl.buckets[ip]
+		b, exists := rl.buckets[key]
 		if !exists {
 			b = &bucket{tokens: rl.rate, lastReset: time.Now()}
-			rl.buckets[ip] = b
+			rl.buckets[key] = b
 		}
 
 		// Reset tokens if interval has passed
diff --git a/workspace-server/internal/middleware/ratelimit_keyfor_test.go b/workspace-server/internal/middleware/ratelimit_keyfor_test.go
new file mode 100644
index 00000000..ac1a227d
--- /dev/null
+++ b/workspace-server/internal/middleware/ratelimit_keyfor_test.go
@@ -0,0 +1,303 @@
+package middleware
+
+import (
+	"context"
+	"crypto/sha256"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// newTestLimiterForKeyFor — same shape as newTestLimiter in ratelimit_test.go
+// but exposes the *gin.Engine and lets the caller inject headers per-request.
+func newTestLimiterForKeyFor(t *testing.T, rate int) *gin.Engine {
+	t.Helper()
+	gin.SetMode(gin.TestMode)
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	rl := NewRateLimiter(rate, 5*time.Second, ctx)
+	r := gin.New()
+	if err := r.SetTrustedProxies(nil); err != nil {
+		t.Fatalf("SetTrustedProxies: %v", err)
+	}
+	r.Use(rl.Middleware())
+	r.GET("/x", func(c *gin.Context) { c.String(http.StatusOK, "ok") })
+	return r
+}
+
+// TestKeyFor_OrgIdHeaderTrumpsBearerAndIP — when X-Molecule-Org-Id is set
+// the bucket is keyed on it regardless of bearer token or IP. This is the
+// load-bearing case for the production SaaS plane: every tenant routed
+// through the same upstream proxy IP gets its own bucket because the
+// CP attaches the org-id header.
+func TestKeyFor_OrgIdHeaderTrumpsBearerAndIP(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	rl := NewRateLimiter(2, 5*time.Second, ctx)
+
+	c, _ := gin.CreateTestContext(httptest.NewRecorder())
+	c.Request = httptest.NewRequest(http.MethodGet, "/x", nil)
+	c.Request.RemoteAddr = "10.0.0.1:1234"
+	c.Request.Header.Set("X-Molecule-Org-Id", "org-aaa")
+	c.Request.Header.Set("Authorization", "Bearer ignored-token-value")
+
+	got := rl.keyFor(c)
+	if got != "org:org-aaa" {
+		t.Errorf("keyFor with org-id header: got %q, want %q", got, "org:org-aaa")
+	}
+}
+
+// TestKeyFor_BearerTokenWhenNoOrgId — the per-tenant Caddy box path:
+// no org-id header (canvas same-origin), but Authorization Bearer is
+// always set by WorkspaceAuth-protected routes. Bucket keyed on the
+// SHA-256 hex of the token so distinct sessions on the same egress IP
+// get distinct buckets — and so the in-memory map can never become a
+// token dump if the process is inspected.
+func TestKeyFor_BearerTokenWhenNoOrgId(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	rl := NewRateLimiter(2, 5*time.Second, ctx)
+
+	c, _ := gin.CreateTestContext(httptest.NewRecorder())
+	c.Request = httptest.NewRequest(http.MethodGet, "/x", nil)
+	c.Request.RemoteAddr = "10.0.0.1:1234"
+	c.Request.Header.Set("Authorization", "Bearer secret-token-abc")
+
+	got := rl.keyFor(c)
+	expectedHash := fmt.Sprintf("%x", sha256.Sum256([]byte("secret-token-abc")))
+	if got != "tok:"+expectedHash {
+		t.Errorf("keyFor with bearer-only: got %q, want %q", got, "tok:"+expectedHash)
+	}
+	// Critical security pin: raw token must never appear in the key.
+	if strings.Contains(got, "secret-token-abc") {
+		t.Errorf("keyFor leaked raw bearer token in bucket key: %q", got)
+	}
+}
+
+// TestKeyFor_IPFallbackWhenNoOrgIdNoBearer — anonymous probes (no auth,
+// no tenant header) fall through to ClientIP keying. This is the only
+// path that depended on the pre-#179 trust-XFF behaviour and is fine
+// to keep IP-keyed because the surface is just /health, /buildinfo,
+// and the registry-boot endpoints.
+func TestKeyFor_IPFallbackWhenNoOrgIdNoBearer(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	rl := NewRateLimiter(2, 5*time.Second, ctx)
+
+	c, _ := gin.CreateTestContext(httptest.NewRecorder())
+	c.Request = httptest.NewRequest(http.MethodGet, "/x", nil)
+	c.Request.RemoteAddr = "203.0.113.1:1234"
+
+	got := rl.keyFor(c)
+	// gin.ClientIP() strips the port — we just need to confirm the prefix
+	// and that the IP appears.
+	if !strings.HasPrefix(got, "ip:") {
+		t.Errorf("keyFor without auth/org headers: got %q, want prefix %q", got, "ip:")
+	}
+	if !strings.Contains(got, "203.0.113.1") {
+		t.Errorf("keyFor IP fallback: got %q, want to contain %q", got, "203.0.113.1")
+	}
+}
+
+// TestRateLimit_TwoOrgsSameIP_IndependentBuckets — the load-bearing
+// regression test for issue #59. Two tenants behind the same upstream
+// proxy must NOT share a bucket; the production SaaS-plane outage was
+// every tenant collapsing to the proxy IP and saturating one bucket.
+//
+// Mutation invariant: removing the org-id branch from keyFor — say,
+// returning "ip:" + c.ClientIP() unconditionally — collapses both
+// tenants back into one bucket and this test fails on the 3rd
+// request because it would 429 instead of 200.
+func TestRateLimit_TwoOrgsSameIP_IndependentBuckets(t *testing.T) {
+	r := newTestLimiterForKeyFor(t, 2)
+
+	exhaust := func(orgID string) {
+		t.Helper()
+		for i := 0; i < 2; i++ {
+			req := httptest.NewRequest(http.MethodGet, "/x", nil)
+			req.RemoteAddr = "10.0.0.1:1234" // SAME upstream proxy IP
+			req.Header.Set("X-Molecule-Org-Id", orgID)
+			w := httptest.NewRecorder()
+			r.ServeHTTP(w, req)
+			if w.Code != http.StatusOK {
+				t.Fatalf("setup orgID=%s req %d: want 200, got %d", orgID, i+1, w.Code)
+			}
+		}
+	}
+
+	exhaust("org-aaa")
+	// org-aaa is now at 0 tokens. org-bbb's bucket must be FRESH.
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	req.RemoteAddr = "10.0.0.1:1234"
+	req.Header.Set("X-Molecule-Org-Id", "org-bbb")
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("org-bbb on same IP must have its own bucket: got %d, want 200 (issue #59 regression)", w.Code)
+	}
+
+	// Confirm org-aaa is still throttled — proves we're not just opening
+	// the gate to everyone.
+	req = httptest.NewRequest(http.MethodGet, "/x", nil)
+	req.RemoteAddr = "10.0.0.1:1234"
+	req.Header.Set("X-Molecule-Org-Id", "org-aaa")
+	w = httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	if w.Code != http.StatusTooManyRequests {
+		t.Errorf("org-aaa exhausted bucket: want 429, got %d", w.Code)
+	}
+}
+
+// TestRateLimit_TwoTokensSameIP_IndependentBuckets — analog of the
+// org-id case for the per-tenant Caddy box: two distinct user
+// sessions on the same egress IP, distinguished only by their bearer
+// tokens, must get independent buckets. This was the path Hongming
+// hit on hongming.moleculesai.app — a single user with multiple
+// browser tabs against one workspace-server box.
+func TestRateLimit_TwoTokensSameIP_IndependentBuckets(t *testing.T) {
+	r := newTestLimiterForKeyFor(t, 2)
+
+	exhaust := func(token string) {
+		t.Helper()
+		for i := 0; i < 2; i++ {
+			req := httptest.NewRequest(http.MethodGet, "/x", nil)
+			req.RemoteAddr = "127.0.0.1:1234" // local Caddy proxy — same for both
+			req.Header.Set("Authorization", "Bearer "+token)
+			w := httptest.NewRecorder()
+			r.ServeHTTP(w, req)
+			if w.Code != http.StatusOK {
+				t.Fatalf("setup token=%s req %d: want 200, got %d", token, i+1, w.Code)
+			}
+		}
+	}
+
+	exhaust("user-a-token")
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	req.RemoteAddr = "127.0.0.1:1234"
+	req.Header.Set("Authorization", "Bearer user-b-token")
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("user-b token on same proxy IP must have its own bucket: got %d, want 200", w.Code)
+	}
+}
+
+// TestRateLimit_SameOrgDifferentTokens_SharedBucket — counter-pin:
+// ensure org-id keying really does collapse all tokens within one
+// org into one bucket. This is the desired behaviour: a tenant that
+// mints multiple tokens shouldn't be able to circumvent its quota
+// by rotating tokens between requests. (The same-IP-different-org
+// test above proves we don't collapse ACROSS orgs; this one proves
+// we DO collapse WITHIN one org.)
+func TestRateLimit_SameOrgDifferentTokens_SharedBucket(t *testing.T) {
+	r := newTestLimiterForKeyFor(t, 2)
+
+	for _, tok := range []string{"token-1", "token-2"} {
+		req := httptest.NewRequest(http.MethodGet, "/x", nil)
+		req.RemoteAddr = "10.0.0.1:1234"
+		req.Header.Set("X-Molecule-Org-Id", "org-shared")
+		req.Header.Set("Authorization", "Bearer "+tok)
+		w := httptest.NewRecorder()
+		r.ServeHTTP(w, req)
+		if w.Code != http.StatusOK {
+			t.Fatalf("setup tok=%s: want 200, got %d", tok, w.Code)
+		}
+	}
+	// Bucket should be exhausted now — third request, even with a fresh
+	// token, must 429 because the org-id is keying it.
+	req := httptest.NewRequest(http.MethodGet, "/x", nil)
+	req.RemoteAddr = "10.0.0.1:1234"
+	req.Header.Set("X-Molecule-Org-Id", "org-shared")
+	req.Header.Set("Authorization", "Bearer token-3")
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	if w.Code != http.StatusTooManyRequests {
+		t.Errorf("rotating tokens within one org should NOT bypass the quota: got %d, want 429", w.Code)
+	}
+}
+
+// TestRateLimit_Middleware_RoutesThroughKeyFor is the AST gate (mirror
+// of #36/#10/#12's gates). Pins the SSOT routing invariant:
+// (*RateLimiter).Middleware MUST call rl.keyFor and MUST NOT carry a
+// direct c.ClientIP() call (= the parallel-impl drift this PR fixes).
+//
+// Mutation invariant: a future PR that re-introduces direct IP keying
+// in Middleware (`ip := c.ClientIP()`) makes this test fail. That's
+// the signal to either (a) extend keyFor's contract to cover the new
+// case OR (b) update this gate with an explicit reason. Either way the
+// drift gets a reviewer's attention before shipping.
+func TestRateLimit_Middleware_RoutesThroughKeyFor(t *testing.T) {
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, "ratelimit.go", nil, parser.ParseComments)
+	if err != nil {
+		t.Fatalf("parse ratelimit.go: %v", err)
+	}
+
+	var fn *ast.FuncDecl
+	ast.Inspect(file, func(n ast.Node) bool {
+		f, ok := n.(*ast.FuncDecl)
+		if !ok {
+			return true
+		}
+		// Match `func (rl *RateLimiter) Middleware() ...`
+		if f.Name.Name != "Middleware" {
+			return true
+		}
+		if f.Recv == nil || len(f.Recv.List) != 1 {
+			return true
+		}
+		star, ok := f.Recv.List[0].Type.(*ast.StarExpr)
+		if !ok {
+			return true
+		}
+		if id, ok := star.X.(*ast.Ident); !ok || id.Name != "RateLimiter" {
+			return true
+		}
+		fn = f
+		return false
+	})
+	if fn == nil {
+		t.Fatal("(*RateLimiter).Middleware not found — was it renamed? update this gate or the SSOT routing assumption")
+	}
+
+	var (
+		callsKeyFor   bool
+		callsClientIP bool
+	)
+	ast.Inspect(fn.Body, func(n ast.Node) bool {
+		call, ok := n.(*ast.CallExpr)
+		if !ok {
+			return true
+		}
+		sel, ok := call.Fun.(*ast.SelectorExpr)
+		if !ok {
+			return true
+		}
+		switch sel.Sel.Name {
+		case "keyFor":
+			callsKeyFor = true
+		case "ClientIP":
+			callsClientIP = true
+		}
+		return true
+	})
+
+	if !callsKeyFor {
+		t.Error("(*RateLimiter).Middleware must call rl.keyFor for SSOT bucket-key derivation — see issue #59. Found no keyFor call.")
+	}
+	if callsClientIP {
+		t.Error("(*RateLimiter).Middleware carries a direct c.ClientIP() call. This is the parallel-impl drift issue #59 fixed. " +
+			"Either route through rl.keyFor OR — if a new use case truly needs direct IP — extend keyFor's contract first and update this gate to allow the specific delta.")
+	}
+}