diff --git a/scripts/prune-worktrees.sh b/scripts/prune-worktrees.sh
index b60e1767..cdeaed2a 100755
--- a/scripts/prune-worktrees.sh
+++ b/scripts/prune-worktrees.sh
@@ -53,6 +53,14 @@
 # on it would protect exactly the trees most in need of removing. ah-6xq.8 was one: merged, closed by
 # nobody, claim still standing, worktree still on disk.
 #
+# What IS part of it, ahead of the four checks: **whether the session holding the tree's bead is
+# alive** (cb-15cw). A producer still planning has made no commit and written nothing, so its tree is
+# clean, at main and quiet past STALE_MINUTES — "nothing can be lost" by git's measure, while the
+# session's ignored files and its branch are still in use. The holder is read from the state files
+# (`bead`, or the handover while the state names none) and believed only when `agent-alive` says
+# the session is running, so a crashed agent's tree is still removed, exactly as the claim rule
+# above intends. `release-bead --worktree` asks the same question for the fleet view's tidy.
+#
 # `git worktree prune` runs first regardless. That only clears registrations whose directory is
 # already gone, which can never lose anything.
 #
@@ -131,6 +139,7 @@ done
 # consumer-root's header for the two roots and why a sweep needs the shared one.
 script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 source "$script_dir/worktree-safety.sh"
+source "$script_dir/session-bead.sh"
 
 repo_root="$("$script_dir/consumer-root" --shared)" || exit 1
 
@@ -177,6 +186,37 @@ is_verifier_tree() {
   [ "$(printf '%s' "$1" | tr '[:upper:]' '[:lower:]')" = "$verifier_lc" ]
 }
 
+# `<bead> <Name>` for every session that is alive and on a bead: its state file's `bead`, or, while
+# that names none, the bead its handover names. Read once per sweep; see the header (cb-15cw).
+live_holders=""
+read_live_holders() {
+  local state_dir="$repo_root/.cerebro/state" file name bead
+  [ -d "$state_dir" ] || return 0
+  for file in "$state_dir"/*.state.json; do
+    [ -f "$file" ] || continue
+    name="$(basename "$file" .state.json)"
+    bead="$(cerebro_session_bead "$state_dir" "$name")"
+    [ -n "$bead" ] || continue
+    if "$script_dir/agent-alive" "$name" >/dev/null 2>&1; then
+      live_holders+="$bead $name"$'\n'
+    fi
+  done
+}
+
+# Prints the name of the live session holding one of the tree's beads, or nothing.
+live_holder_of() {
+  local bead holder
+  while IFS= read -r bead; do
+    [ -n "$bead" ] || continue
+    holder="$(awk -v b="$bead" '$1 == b { print $2; exit }' <<<"$live_holders")"
+    if [ -n "$holder" ]; then
+      printf '%s\n' "$holder"
+      return 0
+    fi
+  done < <(cerebro_worktree_bead "$1")
+  return 0
+}
+
 # Whether the mount and the consumer are ONE GIT REPOSITORY, so that `git worktree list` asked of
 # each returns the same list. When they are, walking "both" walks one list twice — every tree
 # enumerated once per owner, the tallies inflated, and a tree already removed on the first pass
@@ -375,6 +415,8 @@ sweep() {
     fi
   fi
 
+  read_live_holders
+
   # Each line is `<owning repository>|<worktree>`. Every other git call in this loop already
   # passes `$tree` and needs no owner; the four that address the repository do (ah-apw4).
   local owner
@@ -384,12 +426,15 @@ sweep() {
       *) continue ;;
     esac
 
-    local name reason=""
+    local name reason="" holder
     name="$(basename "$tree")"
+    holder="$(live_holder_of "$tree")"
 
     if is_verifier_tree "$name"; then
       reason="it is $verifier_name's verification tree, reset to origin/$default_branch before every use (ah-p31)"
       reclaim_cold_target "$tree" "$name"
+    elif [ -n "$holder" ]; then
+      reason="$holder is alive on it"
     elif [ -n "$(git -C "$tree" status --porcelain 2>/dev/null)" ]; then
       reason="it has uncommitted or untracked changes"
     elif ! cerebro_worktree_landed "$tree" "$(owner_default_branch "$owner")" "$merged_check" "$COLD_TARGET_MINUTES"; then
diff --git a/scripts/release-bead b/scripts/release-bead
index 6728d0ad..0514851b 100755
--- a/scripts/release-bead
+++ b/scripts/release-bead
@@ -80,24 +80,16 @@ usage() {
 
 # NAME is alive and on bead ID: its state file names ID, or names nothing while its handover is
 # absent or names ID. Reads $name, $id and $state.
+#
+# The bead is read by `cerebro_session_bead` (scripts/session-bead.sh), shared with the pruner. A
+# live session naming no bead at all is given the benefit of the doubt here.
 alive_on_bead() {
-  local current="" handed=""
+  local current
   if ! "$script_dir/agent-alive" "$name" >/dev/null 2>&1; then
     return 1
   fi
-  if [[ -f "$state/$name.state.json" ]]; then
-    current="$(jq -r '.bead // empty' "$state/$name.state.json" 2>/dev/null || true)"
-  fi
-  if [[ -f "$state/$name.handover" ]]; then
-    IFS= read -r handed < "$state/$name.handover" || true
-  fi
-  if [[ "$current" == "$id" ]]; then
-    return 0
-  fi
-  if [[ -z "$current" && ( -z "$handed" || "$handed" == "$id" ) ]]; then
-    return 0
-  fi
-  return 1
+  current="$(cerebro_session_bead "$state" "$name")"
+  [[ -z "$current" || "$current" == "$id" ]]
 }
 
 # Prints "<status>US<assignee>US<labels, comma-joined>" for the bead, or fails. US (0x1f), not a
@@ -135,6 +127,7 @@ clear_assignment() {
 }
 
 script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$script_dir/session-bead.sh"
 
 if [[ "${1:-}" == "--worktree" ]]; then
   [[ $# -eq 3 && -n "$2" && -n "$3" ]] || usage
diff --git a/scripts/session-bead.sh b/scripts/session-bead.sh
new file mode 100644
index 00000000..5c3ec1a9
--- /dev/null
+++ b/scripts/session-bead.sh
@@ -0,0 +1,26 @@
+# shellcheck shell=bash
+#
+# scripts/session-bead.sh - the one place bash reads which bead a session says it is on (cb-15cw).
+# Sourced, never executed; it sets no shell options of its own.
+#
+#   cerebro_session_bead <state dir> <Name>
+#       prints the bead <Name>'s state file names, or, while it names none, the bead its handover
+#       names (`scripts/assign-bead` writes the handover before the session's first state write);
+#       prints nothing when neither names one. Always exit 0.
+#
+# Whether the session is ALIVE is not asked here: that is `scripts/agent-alive`, which each caller
+# runs itself. The callers then ask different questions of the answer. `release-bead` asks whether
+# NAME is on bead ID, and gives a live session that names nothing the benefit of the doubt;
+# `prune-worktrees.sh` asks which tree each live session holds, and a session naming nothing
+# holds none.
+cerebro_session_bead() {
+  local state_dir="$1" name="$2" bead=""
+  if [ -f "$state_dir/$name.state.json" ]; then
+    bead="$(jq -r '.bead // empty' "$state_dir/$name.state.json" 2>/dev/null || true)"
+  fi
+  if [ -z "$bead" ] && [ -f "$state_dir/$name.handover" ]; then
+    IFS= read -r bead < "$state_dir/$name.handover" || true
+  fi
+  printf '%s' "$bead"
+  return 0
+}
diff --git a/tests/prune-worktrees.sh b/tests/prune-worktrees.sh
index f3c7699d..297e72f1 100755
--- a/tests/prune-worktrees.sh
+++ b/tests/prune-worktrees.sh
@@ -374,4 +374,68 @@ out="$(cd "$selfmount" && PATH="$sub_stub_dir:$PATH" bash "$selfmount/scripts/pr
   || fail "a self-mounted cerebro enumerated its worktrees twice: $out"
 pass "a self-mounted cerebro is walked once, not twice"
 
+# ================================================================================================
+# A live session's tree is never pruned from under it (cb-15cw).
+#
+# A producer still planning has made no commit and written nothing: its tree is clean, at main and
+# quiet past STALE_MINUTES, so it passed all four checks and was removed mid-pass. The bead's claim
+# is deliberately not the guard (a crashed agent's claim stands for ever); whether the session that
+# holds the bead is ALIVE is. `agent-alive` is stubbed: its own suite proves the marker rule.
+# ================================================================================================
+
+live="$(consumer_new live --origin --link consumer-root project-conf default-branch roster prune-worktrees.sh)"
+alive_names="$work_dir/alive-names"
+: > "$alive_names"
+cat > "$live/.cerebro/cerebro/scripts/agent-alive" <<STUB
+#!/usr/bin/env bash
+grep -qx "\$1" "$alive_names"
+STUB
+chmod +x "$live/.cerebro/cerebro/scripts/agent-alive"
+mkdir -p "$live/.cerebro/state"
+printf '{"state":"working","phase":"design","bead":"cb-live","pid":1}' > "$live/.cerebro/state/Cyclops.state.json"
+
+live_tree() {
+  local tree="$live/.cerebro/worktrees/$1"
+  git_q -C "$live" worktree add -q "$tree" -b "$1-branch"
+  age "$tree"
+}
+live_tree cb-live
+live_tree cb-other
+
+# --- 16. a live session's clean, landed, quiet tree is kept -------------------------------------
+echo Cyclops > "$alive_names"
+out="$(cd "$live" && PATH="$stub_dir:$PATH" bash "$live/.cerebro/cerebro/scripts/prune-worktrees.sh" 2>&1)"
+[ -d "$live/.cerebro/worktrees/cb-live" ] \
+  || fail "a live session's worktree was removed from under it: $out"
+grep -q . <<<"$(git -C "$live" branch --list cb-live-branch)" \
+  || fail "a live session's branch was deleted from under it: $out"
+grep -q "keeping cb-live — Cyclops is alive on it" <<<"$out" \
+  || fail "the keep did not name the live session: $out"
+[ ! -d "$live/.cerebro/worktrees/cb-other" ] \
+  || fail "a tree no live session holds was kept as well: $out"
+pass "a live session's clean, landed, quiet tree is kept, and a tree nobody holds still goes"
+
+# --- 17. once the session is gone, the same tree goes -------------------------------------------
+: > "$alive_names"
+out="$(cd "$live" && PATH="$stub_dir:$PATH" bash "$live/.cerebro/cerebro/scripts/prune-worktrees.sh" 2>&1)"
+[ ! -d "$live/.cerebro/worktrees/cb-live" ] \
+  || fail "a dead session's tree was kept: $out"
+grep -q . <<<"$(git -C "$live" branch --list cb-live-branch)" \
+  && fail "a dead session's branch survived its tree: $out"
+pass "a dead session's tree and branch are removed as before"
+
+# --- 18. a session whose state names no bead yet is held by its handover ------------------------
+# Between `assign-bead` and the session's first state write, the handover is the only record of
+# which bead the session was given.
+live_tree cb-handed
+printf '{"state":"working","pid":1}' > "$live/.cerebro/state/Cyclops.state.json"
+echo cb-handed > "$live/.cerebro/state/Cyclops.handover"
+echo Cyclops > "$alive_names"
+out="$(cd "$live" && PATH="$stub_dir:$PATH" bash "$live/.cerebro/cerebro/scripts/prune-worktrees.sh" 2>&1)"
+[ -d "$live/.cerebro/worktrees/cb-handed" ] \
+  || fail "a live session's handed tree was removed before its first state write: $out"
+grep -q "keeping cb-handed — Cyclops is alive on it" <<<"$out" \
+  || fail "the keep did not name the session its handover names: $out"
+pass "a live session whose state names no bead yet keeps the tree its handover names"
+
 suite_passed