diff --git a/.github/workflows/e2e-api.yml b/.github/workflows/e2e-api.yml
index bc9e629b..782cbedc 100644
--- a/.github/workflows/e2e-api.yml
+++ b/.github/workflows/e2e-api.yml
@@ -172,6 +172,9 @@ jobs:
       - 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: Run poll-mode chat upload E2E (RFC #2891)
+        if: needs.detect-changes.outputs.api == 'true'
+        run: bash tests/e2e/test_poll_mode_chat_upload_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_chat_upload_e2e.sh b/tests/e2e/test_poll_mode_chat_upload_e2e.sh
new file mode 100755
index 00000000..fbed604f
--- /dev/null
+++ b/tests/e2e/test_poll_mode_chat_upload_e2e.sh
@@ -0,0 +1,295 @@
+#!/usr/bin/env bash
+# E2E for poll-mode chat upload (RFC #2891 phases 1-5b).
+#
+# Round-trip: register a workspace as poll-mode (no callback URL) → POST a
+# multi-file chat upload → verify each file becomes (a) one
+# `chat_upload_receive` activity row and (b) one /pending-uploads row → fetch
+# the bytes back via the poll endpoint → ack → verify the row 404s on
+# subsequent fetch. Also pins cross-workspace bleed protection: workspace B
+# cannot read workspace A's pending uploads even with its own valid bearer.
+#
+# Why this exists separately from test_chat_upload_e2e.sh: that script
+# covers the PUSH path (the workspace's own /internal/chat/uploads/ingest).
+# This script covers the POLL path: the same canvas-side request lands on
+# the platform's pendinguploads.Storage instead, and the workspace fetches
+# it later. The two paths share zero handler code on the platform side, so
+# both need their own E2E.
+#
+# 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 UUIDs so reruns
+# don't collide. Best-effort cleanup on EXIT — 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}"
+
+gen_uuid() {
+  if command -v uuidgen >/dev/null 2>&1; then
+    uuidgen | tr '[:upper:]' '[:lower:]'
+  else
+    python3 -c 'import uuid; print(uuid.uuid4())'
+  fi
+}
+WS_A="$(gen_uuid)"
+WS_B="$(gen_uuid)"
+
+# Per-run scratch dir collected under one trap so every assertion-failure
+# path drops the temp files it made (see test_chat_attachments_e2e.sh).
+TMPDIR_E2E=$(mktemp -d -t poll-chat-upload-e2e-XXXXXX)
+
+cleanup() {
+  local rc=$?
+  curl -s -X DELETE "$BASE/workspaces/$WS_A?confirm=true" >/dev/null 2>&1 || true
+  curl -s -X DELETE "$BASE/workspaces/$WS_B?confirm=true" >/dev/null 2>&1 || true
+  rm -rf "$TMPDIR_E2E"
+  exit $rc
+}
+trap cleanup EXIT INT TERM
+
+check() {
+  local desc="$1" expected="$2" 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" expected="$2" 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
+}
+
+echo "=== Poll-Mode Chat Upload E2E ==="
+echo "  base:        $BASE"
+echo "  workspace A: $WS_A"
+echo "  workspace B: $WS_B"
+echo ""
+
+# ---------- Phase 1: register poll-mode workspace ----------
+echo "--- Phase 1: Register poll-mode workspace A ---"
+
+REG_A=$(curl -s -X POST "$BASE/registry/register" \
+  -H "Content-Type: application/json" \
+  -d "{
+    \"id\": \"$WS_A\",
+    \"delivery_mode\": \"poll\",
+    \"agent_card\": {\"name\": \"poll-chat-upload-test-a\"}
+  }")
+check "register accepts poll mode without URL" '"status":"registered"' "$REG_A"
+TOK_A=$(echo "$REG_A" | e2e_extract_token || true)
+[ -n "$TOK_A" ] || { echo "FAIL: no auth_token in register response (ws A)"; FAIL=$((FAIL + 1)); exit 1; }
+
+# ---------- Phase 2: multi-file chat upload ----------
+echo ""
+echo "--- Phase 2: POST /chat/uploads with two files ---"
+
+FILE1="$TMPDIR_E2E/alpha.txt"
+FILE2="$TMPDIR_E2E/beta.txt"
+EXPECTED1="alpha-secret-$(openssl rand -hex 4)"
+EXPECTED2="beta-secret-$(openssl rand -hex 4)"
+printf '%s' "$EXPECTED1" > "$FILE1"
+printf '%s' "$EXPECTED2" > "$FILE2"
+
+UPLOAD=$(curl -s -X POST "$BASE/workspaces/$WS_A/chat/uploads" \
+  -H "Authorization: Bearer $TOK_A" \
+  -F "files=@$FILE1;filename=alpha.txt;type=text/plain" \
+  -F "files=@$FILE2;filename=beta.txt;type=text/plain" \
+  -w "\nHTTP_CODE=%{http_code}\n")
+UPLOAD_CODE=$(echo "$UPLOAD" | grep -oE 'HTTP_CODE=[0-9]+' | cut -d= -f2)
+UPLOAD_BODY=$(echo "$UPLOAD" | sed '/^HTTP_CODE=/,$d')
+
+check_eq "upload returns 200" "200" "$UPLOAD_CODE"
+check "upload response has files array" '"files":' "$UPLOAD_BODY"
+
+# Pull file_ids out of the URI in the response. URI shape is
+# `platform-pending:<wsid>/<file_id>` — proves the response came from the
+# poll-mode branch, not the push-mode internal-ingest branch.
+URI1=$(echo "$UPLOAD_BODY" | python3 -c 'import sys,json; d=json.load(sys.stdin); print(d["files"][0]["uri"])')
+URI2=$(echo "$UPLOAD_BODY" | python3 -c 'import sys,json; d=json.load(sys.stdin); print(d["files"][1]["uri"])')
+check "URI 1 has platform-pending: scheme" "platform-pending:$WS_A/" "$URI1"
+check "URI 2 has platform-pending: scheme" "platform-pending:$WS_A/" "$URI2"
+
+FID1="${URI1##*/}"
+FID2="${URI2##*/}"
+[ -n "$FID1" ] && [ -n "$FID2" ] || { echo "FAIL: could not extract file IDs"; FAIL=$((FAIL + 1)); exit 1; }
+echo "  file_id 1: $FID1"
+echo "  file_id 2: $FID2"
+
+# ---------- Phase 3: activity rows visible to the workspace ----------
+echo ""
+echo "--- Phase 3: /activity shows two chat_upload_receive rows ---"
+
+# activity_logs INSERTs run in a goroutine — give them a moment.
+sleep 1
+ACT=$(curl -s --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/activity?type=a2a_receive&limit=20")
+check "activity feed has the alpha file"      "$FID1" "$ACT"
+check "activity feed has the beta file"       "$FID2" "$ACT"
+check "activity rows tagged chat_upload_receive" '"method":"chat_upload_receive"' "$ACT"
+check "activity rows record alpha mimetype"   '"mimeType":"text/plain"' "$ACT"
+
+CHAT_UPLOAD_COUNT=$(echo "$ACT" | python3 -c '
+import json, sys
+rows = json.load(sys.stdin)
+n = sum(1 for r in rows if (r.get("method") or "") == "chat_upload_receive")
+print(n)
+')
+check_eq "exactly two chat_upload_receive rows" "2" "$CHAT_UPLOAD_COUNT"
+
+# ---------- Phase 4: GET /pending-uploads/:file_id/content ----------
+echo ""
+echo "--- Phase 4: Fetch content for each pending upload ---"
+
+GOT1=$(curl -s --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/content")
+check_eq "alpha bytes round-trip" "$EXPECTED1" "$GOT1"
+
+GOT2=$(curl -s --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID2/content")
+check_eq "beta bytes round-trip" "$EXPECTED2" "$GOT2"
+
+# Mimetype + Content-Disposition headers should match what was uploaded.
+HEAD1=$(curl -s -D - -o /dev/null --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/content")
+check "alpha response carries text/plain Content-Type" "Content-Type: text/plain" "$HEAD1"
+check "alpha response carries Content-Disposition with filename" 'filename="alpha.txt"' "$HEAD1"
+
+# ---------- Phase 5: idempotent re-fetch (until ack) ----------
+echo ""
+echo "--- Phase 5: Re-fetch before ack returns the same bytes ---"
+
+RE_GOT1=$(curl -s --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/content")
+check_eq "re-fetch returns same alpha bytes" "$EXPECTED1" "$RE_GOT1"
+
+# ---------- Phase 6: ack each row ----------
+echo ""
+echo "--- Phase 6: Ack each pending upload ---"
+
+ACK1=$(curl -s -X POST --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/ack")
+check "alpha ack returns acked:true" '"acked":true' "$ACK1"
+
+ACK2=$(curl -s -X POST --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID2/ack")
+check "beta ack returns acked:true" '"acked":true' "$ACK2"
+
+# Re-ack should still 200 (idempotent — the row's gone but the workspace's
+# at-least-once intent was already honored, and the second ack hits the
+# raced path which also returns 200).
+RE_ACK1=$(curl -s -w '\n%{http_code}' -X POST --max-time "$TIMEOUT" \
+  -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/ack")
+RE_ACK1_CODE=$(printf '%s' "$RE_ACK1" | tail -n1)
+# Acked rows return 404 on Get-before-Ack (the row's still in the table
+# but Get filters acked_at IS NULL); workspace would not normally re-ack
+# since it already saw the success. Accept both 200 and 404 here so the
+# test pins the contract without being brittle on the inner ordering.
+case "$RE_ACK1_CODE" in
+  200|404)
+    echo "PASS: re-ack returns 200 or 404 ($RE_ACK1_CODE)"
+    PASS=$((PASS + 1))
+    ;;
+  *)
+    echo "FAIL: re-ack returned unexpected $RE_ACK1_CODE"
+    FAIL=$((FAIL + 1))
+    ;;
+esac
+
+# ---------- Phase 7: GET content after ack returns 404 ----------
+echo ""
+echo "--- Phase 7: Acked file 404s on subsequent fetch ---"
+
+POST_ACK=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$FID1/content")
+POST_ACK_CODE=$(printf '%s' "$POST_ACK" | tail -n1)
+check_eq "acked alpha returns HTTP 404" "404" "$POST_ACK_CODE"
+
+# ---------- Phase 8: cross-workspace bleed protection ----------
+echo ""
+echo "--- Phase 8: Workspace B cannot read workspace A's pending uploads ---"
+
+# Stage a fresh upload on workspace A so we have an UN-acked row to probe.
+PROBE_FILE="$TMPDIR_E2E/probe.txt"
+printf '%s' "probe-bytes-$(openssl rand -hex 4)" > "$PROBE_FILE"
+PROBE_UP=$(curl -s -X POST "$BASE/workspaces/$WS_A/chat/uploads" \
+  -H "Authorization: Bearer $TOK_A" \
+  -F "files=@$PROBE_FILE;filename=probe.txt;type=text/plain")
+PROBE_FID=$(echo "$PROBE_UP" | python3 -c 'import sys,json; d=json.load(sys.stdin); print(d["files"][0]["uri"].split("/")[-1])')
+[ -n "$PROBE_FID" ] || { echo "FAIL: probe upload returned no file_id"; FAIL=$((FAIL + 1)); exit 1; }
+
+# Register a SECOND poll-mode workspace and capture its bearer.
+REG_B=$(curl -s -X POST "$BASE/registry/register" \
+  -H "Content-Type: application/json" \
+  -d "{
+    \"id\": \"$WS_B\",
+    \"delivery_mode\": \"poll\",
+    \"agent_card\": {\"name\": \"poll-chat-upload-test-b\"}
+  }")
+check "second workspace registers" '"status":"registered"' "$REG_B"
+TOK_B=$(echo "$REG_B" | e2e_extract_token || true)
+[ -n "$TOK_B" ] || { echo "FAIL: no auth_token (ws B)"; FAIL=$((FAIL + 1)); exit 1; }
+
+# B's bearer hitting B's URL with A's file_id → 404 (handler checks the row's
+# workspace_id matches the URL :id, not the bearer's workspace).
+CROSS_RESP=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" \
+  -H "Authorization: Bearer $TOK_B" \
+  "$BASE/workspaces/$WS_B/pending-uploads/$PROBE_FID/content")
+CROSS_CODE=$(printf '%s' "$CROSS_RESP" | tail -n1)
+check_eq "B's URL with A's file_id returns 404" "404" "$CROSS_CODE"
+
+# B's bearer hitting A's URL → 401 (wsAuth pins bearer to :id). This is the
+# strictest cross-workspace check: a presented-but-wrong bearer is rejected
+# in EVERY platform posture (dev-mode fail-open only triggers when no bearer
+# is presented at all — invalid tokens always 401).
+WRONG_BEARER=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" \
+  -H "Authorization: Bearer $TOK_B" \
+  "$BASE/workspaces/$WS_A/pending-uploads/$PROBE_FID/content")
+WRONG_CODE=$(printf '%s' "$WRONG_BEARER" | tail -n1)
+check_eq "B's bearer on A's URL returns 401" "401" "$WRONG_CODE"
+
+# NB: a fully bearerless request to /pending-uploads/:fid/content returns
+# 401 ONLY when the platform has MOLECULE_ENV != development (production /
+# staging). On local-dev with MOLECULE_ENV=development the wsauth middleware
+# fail-opens for bearerless requests so the canvas at :3000 can talk to the
+# platform at :8080 without per-call token plumbing — see middleware/
+# devmode.go. The strict bearerless-401 contract is covered by the wsauth
+# unit + middleware tests; we don't reassert it here because the result
+# depends on platform posture, not the poll-mode upload contract.
+
+# ---------- Phase 9: invalid file_id rejected at the URL parser ----------
+echo ""
+echo "--- Phase 9: Invalid file_id returns 400 ---"
+
+BAD_FID=$(curl -s -w '\n%{http_code}' --max-time "$TIMEOUT" \
+  -H "Authorization: Bearer $TOK_A" \
+  "$BASE/workspaces/$WS_A/pending-uploads/not-a-uuid/content")
+BAD_FID_CODE=$(printf '%s' "$BAD_FID" | tail -n1)
+check_eq "invalid file_id UUID returns 400" "400" "$BAD_FID_CODE"
+
+# ---------- Results ----------
+echo ""
+echo "=== Results: $PASS passed, $FAIL failed ==="
+[ "$FAIL" -eq 0 ]