diff --git a/tests/e2e/lib/collision-proof-slug.sh b/tests/e2e/lib/collision-proof-slug.sh
index 8058cf5e6..f2ed256fa 100755
--- a/tests/e2e/lib/collision-proof-slug.sh
+++ b/tests/e2e/lib/collision-proof-slug.sh
@@ -85,12 +85,13 @@ make_collision_proof_slug_suffix() {
   fi
 
   # Suffix layout: <date:8> + - + <run_id:N> + - + <uuid:8> = N+18 chars.
-  # Full slug: <prefix_len> + 1 (separator) + (N+18) = prefix_len + N + 19.
-  # Cap: prefix_len + N + 19 <= CP_ORG_SLUG_MAX_LEN
-  #      => N <= CP_ORG_SLUG_MAX_LEN - prefix_len - 19
-  local run_id_budget=$(( CP_ORG_SLUG_MAX_LEN - prefix_len - 19 ))
+  # The caller's literal prefix already includes its trailing separator,
+  # so the full slug is <prefix_len> + (N+18) = prefix_len + N + 18.
+  # Cap: prefix_len + N + 18 <= CP_ORG_SLUG_MAX_LEN
+  #      => N <= CP_ORG_SLUG_MAX_LEN - prefix_len - 18
+  local run_id_budget=$(( CP_ORG_SLUG_MAX_LEN - prefix_len - 18 ))
   if [ "$run_id_budget" -lt 1 ]; then
-    echo "make_collision_proof_slug_suffix: caller prefix (${prefix_len} chars) too long for CP_ORG_SLUG_MAX_LEN=${CP_ORG_SLUG_MAX_LEN}; uuid anchor (8 chars) + date (8 chars) + 3 separators = 19 chars minimum, no room for run_id segment. Shorten the prefix literal in the SLUG= assignment." >&2
+    echo "make_collision_proof_slug_suffix: caller prefix (${prefix_len} chars) too long for CP_ORG_SLUG_MAX_LEN=${CP_ORG_SLUG_MAX_LEN}; date (8 chars) + uuid anchor (8 chars) + 2 separators = 18 chars minimum after the prefix, no room for run_id segment. Shorten the prefix literal in the SLUG= assignment." >&2
     return 1
   fi
 
diff --git a/tests/e2e/test_collision_proof_slug_unit.sh b/tests/e2e/test_collision_proof_slug_unit.sh
index 3f264c747..01aec80b6 100755
--- a/tests/e2e/test_collision_proof_slug_unit.sh
+++ b/tests/e2e/test_collision_proof_slug_unit.sh
@@ -212,6 +212,37 @@ test_e2e_pv_prefix_caps_to_32() {
 
 test_e2e_pv_prefix_caps_to_32 || failed=$((failed+1))
 
+# core#2839 follow-up: the concierge "creates workspace" staging E2E
+# uses a 13-char literal prefix (`e2e-cncrg-mk-`). With the corrected
+# helper budget (prefix_len + N + 18 <= CP_ORG_SLUG_MAX_LEN) this
+# prefix leaves room for a 1-char run_id segment plus the 8-hex uuid
+# anchor, keeping the full slug ≤32 chars and matching the CP regex
+# ^[a-z][a-z0-9-]{2,31}$.
+test_e2e_cncrg_mk_prefix_caps_to_32() {
+  local s
+  s="e2e-cncrg-mk-$(make_collision_proof_slug_suffix "20260614-498600-1" 13)"
+  if ! assert_collision_proof_slug "$s"; then
+    echo "FAIL: test_e2e_cncrg_mk_prefix_caps_to_32 — slug '$s' (len=${#s}) failed assert_collision_proof_slug"
+    return 1
+  fi
+  if [ "${#s}" -gt 32 ]; then
+    echo "FAIL: test_e2e_cncrg_mk_prefix_caps_to_32 — slug '$s' is ${#s} chars (want <= 32 to match CP regex ^[a-z][a-z0-9-]{2,31}$)"
+    return 1
+  fi
+  if ! printf '%s' "$s" | grep -q "^e2e-cncrg-mk-"; then
+    echo "FAIL: test_e2e_cncrg_mk_prefix_caps_to_32 — slug '$s' does not start with 'e2e-cncrg-mk-'"
+    return 1
+  fi
+  if ! printf '%s' "$s" | grep -qE '^[a-z][a-z0-9-]{2,31}$'; then
+    echo "FAIL: test_e2e_cncrg_mk_prefix_caps_to_32 — slug '$s' does NOT match CP regex ^[a-z][a-z0-9-]{2,31}\$"
+    return 1
+  fi
+  echo "PASS: test_e2e_cncrg_mk_prefix_caps_to_32 (slug=$s, len=${#s})"
+  return 0
+}
+
+test_e2e_cncrg_mk_prefix_caps_to_32 || failed=$((failed+1))
+
 if [ "$failed" -gt 0 ]; then
   echo "FAILED: $failed test(s)"
   exit 1
diff --git a/tests/e2e/test_staging_concierge_creates_workspace_e2e.sh b/tests/e2e/test_staging_concierge_creates_workspace_e2e.sh
index c1b7ce545..9c239e4b8 100755
--- a/tests/e2e/test_staging_concierge_creates_workspace_e2e.sh
+++ b/tests/e2e/test_staging_concierge_creates_workspace_e2e.sh
@@ -93,11 +93,11 @@ REQUIRE_LIVE="${E2E_REQUIRE_LIVE:-0}"
 source "$(dirname "$0")/lib/collision-proof-slug.sh"
 
 # The workspace name we will ask the concierge to create. The literal
-# `e2e-cncrg-worker-` prefix is visible to the lint (so the SLUG=
+# `e2e-cncrg-w-` prefix is visible to the lint (so the SLUG=
 # has a covered e2e- prefix in the assignment); the uuid suffix
 # makes the name unique per run so a poll for it can never collide
 # with a sibling run's name.
-WORKER_NAME="e2e-cncrg-worker-$(make_collision_proof_slug_suffix "${E2E_RUN_ID:-}" 17)"
+WORKER_NAME="e2e-cncrg-w-$(make_collision_proof_slug_suffix "${E2E_RUN_ID:-}" 12)"
 WORKER_NAME=$(echo "$WORKER_NAME" | tr -cd 'a-zA-Z0-9-' | head -c 48)
 # Exported so the find_worker_by_name python subshell (run in a pipe) reads it
 # via os.environ — a bare shell var would not survive into the subprocess env.