diff --git a/.github/workflows/e2e-api.yml b/.github/workflows/e2e-api.yml
index 2023c0ef..9acc570f 100644
--- a/.github/workflows/e2e-api.yml
+++ b/.github/workflows/e2e-api.yml
@@ -169,6 +169,9 @@ jobs:
       - name: Run priority-runtimes E2E (claude-code + hermes — skips when keys absent)
         if: needs.detect-changes.outputs.api == 'true'
         run: bash tests/e2e/test_priority_runtimes_e2e.sh
+      - name: Run poll-mode + since_id cursor E2E (#2339)
+        if: needs.detect-changes.outputs.api == 'true'
+        run: bash tests/e2e/test_poll_mode_e2e.sh
       - name: Dump platform log on failure
         if: failure() && needs.detect-changes.outputs.api == 'true'
         run: cat workspace-server/platform.log || true
diff --git a/tests/e2e/test_poll_mode_e2e.sh b/tests/e2e/test_poll_mode_e2e.sh
new file mode 100755
index 00000000..e4dd22bc
--- /dev/null
+++ b/tests/e2e/test_poll_mode_e2e.sh
@@ -0,0 +1,308 @@
+#!/usr/bin/env bash
+# E2E for delivery_mode=poll + since_id cursor (#2339).
+#
+# Round-trip: register a workspace as poll-mode (no URL) → POST A2A to it →
+# verify the proxy short-circuits to {status:"queued"} → verify the message
+# appears in /activity → verify the since_id cursor returns ONLY new events
+# in ASC order → verify a stale cursor returns 410.
+#
+# Requires: platform running on localhost:8080 with migrations applied.
+#   bash workspace-server/scripts/dev-start.sh
+#   bash workspace-server/scripts/run-migrations.sh
+#
+# Idempotent: each run uses fresh per-script workspace ids so reruns don't
+# collide. Does NOT call e2e_cleanup_all_workspaces — see
+# `feedback_never_run_cluster_cleanup_tests_on_live_platform.md`.
+
+set -euo pipefail
+
+source "$(dirname "$0")/_lib.sh"
+
+PASS=0
+FAIL=0
+TIMEOUT="${A2A_TIMEOUT:-30}"
+
+# Per-run unique ids — workspaces.id is a UUID column, so we generate
+# real v4 UUIDs. A "ws-<tag>" string fails the pq UUID cast and surfaces
+# as opaque "registration failed" (caught against this very test in CI
+# before merge — the failure mode that motivates the helper).
+gen_uuid() {
+  if command -v uuidgen >/dev/null 2>&1; then
+    uuidgen | tr '[:upper:]' '[:lower:]'
+  else
+    python3 -c 'import uuid; print(uuid.uuid4())'
+  fi
+}
+POLL_WS_ID="$(gen_uuid)"
+CALLER_WS_ID="$(gen_uuid)"
+# Phase 2 uses a separate UUID for its invalid-mode probe so a rerun
+# can't poison POLL_WS_ID's row with a bad upsert (the 400 path doesn't
+# touch DB, but defense in depth).
+INVALID_PROBE_ID="$(gen_uuid)"
+
+cleanup() {
+  local rc=$?
+  # Best-effort delete; non-fatal if the row was never created.
+  curl -s -X DELETE "$BASE/workspaces/$POLL_WS_ID" >/dev/null || true
+  curl -s -X DELETE "$BASE/workspaces/$CALLER_WS_ID" >/dev/null || true
+  exit $rc
+}
+trap cleanup EXIT
+
+check() {
+  local desc="$1"
+  local expected="$2"
+  local actual="$3"
+  if echo "$actual" | grep -qF -- "$expected"; then
+    echo "PASS: $desc"
+    PASS=$((PASS + 1))
+  else
+    echo "FAIL: $desc"
+    echo "  expected to contain: $expected"
+    echo "  got: $(echo "$actual" | head -10)"
+    FAIL=$((FAIL + 1))
+  fi
+}
+
+check_eq() {
+  local desc="$1"
+  local expected="$2"
+  local actual="$3"
+  if [ "$actual" = "$expected" ]; then
+    echo "PASS: $desc"
+    PASS=$((PASS + 1))
+  else
+    echo "FAIL: $desc"
+    echo "  expected: $expected"
+    echo "  got:      $actual"
+    FAIL=$((FAIL + 1))
+  fi
+}
+
+check_not_contains() {
+  local desc="$1"
+  local unexpected="$2"
+  local actual="$3"
+  if echo "$actual" | grep -qF -- "$unexpected"; then
+    echo "FAIL: $desc"
+    echo "  should NOT contain: $unexpected"
+    FAIL=$((FAIL + 1))
+  else
+    echo "PASS: $desc"
+    PASS=$((PASS + 1))
+  fi
+}
+
+echo "=== Poll-Mode + since_id Cursor E2E (#2339) ==="
+echo "  base: $BASE"
+echo "  poll workspace: $POLL_WS_ID"
+echo "  caller workspace: $CALLER_WS_ID"
+echo ""
+
+# ---------- Phase 1: register as poll-mode ----------
+echo "--- Phase 1: Register poll-mode workspace (no URL) ---"
+
+# A poll-mode workspace registers WITHOUT a URL — that's the contract from
+# PR 1 (#2348). The agent_card is required; everything else is optional.
+REG_RESP=$(curl -s -X POST "$BASE/registry/register" \
+  -H "Content-Type: application/json" \
+  -d "{
+    \"id\": \"$POLL_WS_ID\",
+    \"delivery_mode\": \"poll\",
+    \"agent_card\": {\"name\": \"poll-mode-test\"}
+  }")
+
+check "register accepts poll mode without URL" '"status":"registered"' "$REG_RESP"
+check "register response echoes delivery_mode=poll"  '"delivery_mode":"poll"' "$REG_RESP"
+
+# Capture the auth token for subsequent /activity reads (Phase 30.1).
+POLL_TOKEN=$(echo "$REG_RESP" | e2e_extract_token || true)
+if [ -z "$POLL_TOKEN" ]; then
+  echo "WARN: no auth_token in register response — token-required reads will fail"
+fi
+
+# ---------- Phase 2: invalid mode rejected ----------
+echo ""
+echo "--- Phase 2: Invalid delivery_mode rejected ---"
+
+INVALID_RESP=$(curl -s -w '\n%{http_code}' -X POST "$BASE/registry/register" \
+  -H "Content-Type: application/json" \
+  -d "{
+    \"id\": \"$INVALID_PROBE_ID\",
+    \"delivery_mode\": \"webhook\",
+    \"agent_card\": {\"name\": \"bad\"}
+  }")
+INVALID_CODE=$(printf '%s' "$INVALID_RESP" | tail -n1)
+INVALID_BODY=$(printf '%s' "$INVALID_RESP" | sed '$d')
+
+check_eq "register rejects unknown delivery_mode (HTTP 400)" "400" "$INVALID_CODE"
+check "error mentions delivery_mode" "delivery_mode" "$INVALID_BODY"
+
+# ---------- Phase 3: A2A short-circuits to {status:"queued"} ----------
+echo ""
+echo "--- Phase 3: A2A to poll-mode workspace short-circuits ---"
+
+A2A_RESP=$(curl -s --max-time "$TIMEOUT" -X POST "$BASE/workspaces/$POLL_WS_ID/a2a" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "jsonrpc": "2.0",
+    "id": "msg-1",
+    "method": "message/send",
+    "params": {
+      "message": {
+        "role": "user",
+        "parts": [{"type": "text", "text": "hello-from-e2e-1"}]
+      }
+    }
+  }')
+
+check "poll-mode A2A returns queued status" '"status":"queued"' "$A2A_RESP"
+check "queued response echoes delivery_mode=poll" '"delivery_mode":"poll"' "$A2A_RESP"
+check "queued response echoes the JSON-RPC method" '"method":"message/send"' "$A2A_RESP"
+
+# ---------- Phase 4: queued message appears in /activity ----------
+echo ""
+echo "--- Phase 4: Queued message visible via /activity ---"
+
+# The activity_logs INSERT runs in a goroutine — give it a moment.
+sleep 1
+
+# Use bearer token if we got one; some platforms require it on /activity.
+ACTIVITY_AUTH=()
+[ -n "${POLL_TOKEN:-}" ] && ACTIVITY_AUTH=(-H "Authorization: Bearer $POLL_TOKEN")
+
+ACT_RESP=$(curl -s --max-time "$TIMEOUT" "${ACTIVITY_AUTH[@]}" \
+  "$BASE/workspaces/$POLL_WS_ID/activity?type=a2a_receive&limit=10")
+
+check "activity feed has the queued message text" "hello-from-e2e-1" "$ACT_RESP"
+check "activity_type is a2a_receive"             '"activity_type":"a2a_receive"' "$ACT_RESP"
+check "method preserved on the activity row"     '"method":"message/send"' "$ACT_RESP"
+
+# Pull the most-recent activity_id for use as a cursor.
+FIRST_ACTIVITY_ID=$(echo "$ACT_RESP" | python3 -c "
+import json, sys
+rows = json.load(sys.stdin)
+if not rows:
+    print('')
+else:
+    # Default ordering is DESC (newest-first) when no since_id is set.
+    print(rows[0]['id'])
+")
+
+if [ -z "$FIRST_ACTIVITY_ID" ]; then
+  echo "FAIL: could not extract activity_id from /activity response"
+  FAIL=$((FAIL + 1))
+  exit 1
+fi
+echo "  cursor candidate: $FIRST_ACTIVITY_ID"
+
+# ---------- Phase 5: since_id returns only events strictly after ----------
+echo ""
+echo "--- Phase 5: since_id cursor returns ASC, strictly-after ---"
+
+# Send a SECOND A2A message; it must appear in the cursor-filtered feed,
+# the FIRST message must NOT (cursor is strictly-after).
+A2A_RESP2=$(curl -s --max-time "$TIMEOUT" -X POST "$BASE/workspaces/$POLL_WS_ID/a2a" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "jsonrpc": "2.0",
+    "id": "msg-2",
+    "method": "message/send",
+    "params": {
+      "message": {
+        "role": "user",
+        "parts": [{"type": "text", "text": "hello-from-e2e-2"}]
+      }
+    }
+  }')
+check "second A2A also queues" '"status":"queued"' "$A2A_RESP2"
+
+sleep 1
+
+CURSOR_RESP=$(curl -s --max-time "$TIMEOUT" "${ACTIVITY_AUTH[@]}" \
+  "$BASE/workspaces/$POLL_WS_ID/activity?type=a2a_receive&since_id=$FIRST_ACTIVITY_ID&limit=10")
+
+check              "since_id feed includes the new message"          "hello-from-e2e-2" "$CURSOR_RESP"
+check_not_contains "since_id feed excludes the cursor row itself"  "hello-from-e2e-1" "$CURSOR_RESP"
+
+# Verify ASC ordering: in a fresh cursor window with two new events the
+# array's first element must be the OLDER one (the test only sends one
+# event after the cursor, so this case is trivially "exactly one row";
+# the next sub-phase strengthens this with a second event).
+A2A_RESP3=$(curl -s --max-time "$TIMEOUT" -X POST "$BASE/workspaces/$POLL_WS_ID/a2a" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "jsonrpc": "2.0",
+    "id": "msg-3",
+    "method": "message/send",
+    "params": {
+      "message": {
+        "role": "user",
+        "parts": [{"type": "text", "text": "hello-from-e2e-3"}]
+      }
+    }
+  }')
+check "third A2A queues" '"status":"queued"' "$A2A_RESP3"
+
+sleep 1
+
+ASC_RESP=$(curl -s --max-time "$TIMEOUT" "${ACTIVITY_AUTH[@]}" \
+  "$BASE/workspaces/$POLL_WS_ID/activity?type=a2a_receive&since_id=$FIRST_ACTIVITY_ID&limit=10")
+
+# rows[0] should be msg-2 (older), rows[-1] should be msg-3 (newer) — that's
+# ASC. If the server still defaulted to DESC, rows[0] would be msg-3.
+ASC_FIRST=$(echo "$ASC_RESP" | python3 -c "
+import json, sys
+rows = json.load(sys.stdin)
+def text_of(r):
+    body = r.get('request_body') or {}
+    parts = (body.get('params') or {}).get('message', {}).get('parts') or []
+    return ''.join(p.get('text','') for p in parts if p.get('type')=='text')
+if len(rows) < 2:
+    print('NEED2_GOT_'+str(len(rows)))
+else:
+    print(text_of(rows[0]) + '|' + text_of(rows[-1]))
+")
+check_eq "since_id feed orders ASC (oldest-new first, newest-new last)" \
+  "hello-from-e2e-2|hello-from-e2e-3" "$ASC_FIRST"
+
+# ---------- Phase 6: stale cursor returns 410 ----------
+echo ""
+echo "--- Phase 6: Stale / unknown cursor returns 410 ---"
+
+GONE_RESP=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" "${ACTIVITY_AUTH[@]}" \
+  "$BASE/workspaces/$POLL_WS_ID/activity?since_id=00000000-0000-0000-0000-000000000000")
+GONE_CODE=$(printf '%s' "$GONE_RESP" | tail -n1)
+GONE_BODY=$(printf '%s' "$GONE_RESP" | sed '$d')
+
+check_eq "unknown since_id returns HTTP 410 Gone" "410" "$GONE_CODE"
+check "410 body explains how to recover" "since_id" "$GONE_BODY"
+
+# ---------- Phase 7: cross-workspace cursor isolation ----------
+echo ""
+echo "--- Phase 7: Cross-workspace cursor isolation ---"
+
+# Register a SECOND poll-mode workspace and try to read its activity
+# feed using a cursor from the FIRST workspace. Must 410 — the cursor
+# is workspace-scoped to prevent UUID-guessing peeks.
+REG2=$(curl -s -X POST "$BASE/registry/register" \
+  -H "Content-Type: application/json" \
+  -d "{
+    \"id\": \"$CALLER_WS_ID\",
+    \"delivery_mode\": \"poll\",
+    \"agent_card\": {\"name\": \"poll-cross-test\"}
+  }")
+check "second poll-mode workspace registers" '"status":"registered"' "$REG2"
+CALLER_TOKEN=$(echo "$REG2" | e2e_extract_token || true)
+CROSS_AUTH=()
+[ -n "${CALLER_TOKEN:-}" ] && CROSS_AUTH=(-H "Authorization: Bearer $CALLER_TOKEN")
+
+CROSS_RESP=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" "${CROSS_AUTH[@]}" \
+  "$BASE/workspaces/$CALLER_WS_ID/activity?since_id=$FIRST_ACTIVITY_ID")
+CROSS_CODE=$(printf '%s' "$CROSS_RESP" | tail -n1)
+check_eq "cross-workspace cursor blocked with 410 (no info leak)" "410" "$CROSS_CODE"
+
+# ---------- Results ----------
+echo ""
+echo "=== Results: $PASS passed, $FAIL failed ==="
+[ "$FAIL" -eq 0 ]