diff --git a/.bashrc b/.bashrc
index 8de91f1..9fda9bf 100644
--- a/.bashrc
+++ b/.bashrc
@@ -303,6 +303,10 @@ git-health() {
 # otherwise. It prints from cache so it never costs a prompt, and refreshes in
 # the background when that cache goes stale.
 fleet-stranded() { bash "$HOME/dev/dotfiles/scripts/fleet/stranded-work.sh" "${1:-}"; }
+# Companion to the above: stranded-work asks "is any work trapped here?",
+# fleet-gc asks "is any checkout still here after its work shipped?". Dry-run
+# unless given --go; it deletes checkouts, so that default is deliberate.
+fleet-gc() { bash "$HOME/dev/dotfiles/scripts/fleet/gc-merged-worktrees.sh" "${1:-}"; }
 
 if [ -z "${BASH_EXECUTION_STRING:-}" ] && [ -f "$HOME/dev/dotfiles/scripts/fleet/stranded-work.sh" ]; then
     bash "$HOME/dev/dotfiles/scripts/fleet/stranded-work.sh" --shell 2>/dev/null
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e6f857e..d6af7d9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -90,6 +90,14 @@ jobs:
       - name: The stranded-work guard can go red, and stays quiet when it should
         run: bash scripts/fleet/test-stranded-work.sh
 
+      # This one DELETES CHECKOUTS, so its only interesting failure is a false
+      # positive. Every refusal in the predicate is a case that would otherwise
+      # have destroyed the single existing copy of some work, and each is pinned
+      # separately — a combined "unsafe" fixture is exactly what hides one guard
+      # silently inverting.
+      - name: The worktree GC refuses everything it should
+        run: bash scripts/fleet/test-gc-merged-worktrees.sh
+
       # The sweep decides what ships in every repo that calls it, so it is the
       # last script here that should be untested — and until now it was. These
       # run the REAL script against a fake `gh`, exercising shipped control flow
diff --git a/scripts/fleet/gc-merged-worktrees.sh b/scripts/fleet/gc-merged-worktrees.sh
new file mode 100755
index 0000000..95f5af7
--- /dev/null
+++ b/scripts/fleet/gc-merged-worktrees.sh
@@ -0,0 +1,141 @@
+#!/usr/bin/env bash
+#
+# Remove the worktrees whose work already shipped.
+#
+# The fleet works almost entirely in per-session `git worktree` checkouts. They
+# are created automatically and removed by nobody, so they accumulate: on
+# 2026-08-26 there were 24 of them holding 5.2 GB, and every single one belonged
+# to a PR that had already merged. Twenty-three were byte-for-byte clean.
+#
+# That is a recurring manual sweep, which is the definition of something that
+# should be a committed script rather than a thing an agent re-derives. But a
+# script that deletes checkouts has to be paranoid, so the whole design is the
+# four-part predicate in safe_to_remove(): a worktree is removable only if it
+# was PUSHED, is CLEAN, is UNUSED, and GitHub says MERGED.
+#
+# Dry-run is the default. Nothing is deleted without `--go`.
+#
+# Usage:
+#   gc-merged-worktrees.sh          # show what would go (default)
+#   gc-merged-worktrees.sh --go     # actually remove
+#
+# Env: FLEET_ROOT (default ~/dev), SESSIONS_DIR (default ~/.claude/sessions)
+
+set -uo pipefail
+
+ROOT="${FLEET_ROOT:-$HOME/dev}"
+SESSIONS_DIR="${SESSIONS_DIR:-$HOME/.claude/sessions}"
+
+GO=0
+case "${1:-}" in
+  --go) GO=1 ;;
+  --dry|"") GO=0 ;;
+  *) echo "unknown argument: $1" >&2; exit 2 ;;
+esac
+
+# ---------------------------------------------------------------------------
+# The predicate. Pure except for the four facts it is handed, so the tests can
+# drive every branch without building a GitHub repo or a live agent session.
+#
+# Echoes "ok" or the reason it refused. Returns 0 only for "ok".
+#
+#   pushed   : "yes" if the branch has an upstream configured. A branch with no
+#              upstream never left the machine — removing it destroys the only
+#              copy. This is the one that must never be loosened.
+#   dirty_n  : count of uncommitted files. Any is a refusal; a worktree is
+#              exactly where someone's unfinished edit lives.
+#   in_use   : "yes" if a live session's cwd is inside it.
+#   pr_state : whatever `gh pr list --state all` said, or "" if it said nothing.
+#              MERGED is required — CLOSED means abandoned, and abandoned work
+#              is still a decision someone might want to revisit.
+# ---------------------------------------------------------------------------
+safe_to_remove() { # <pushed> <dirty_n> <in_use> <pr_state>
+  local pushed="$1" dirty_n="$2" in_use="$3" pr_state="$4"
+  if [ "$pushed" != yes ];  then echo "never pushed — this is the only copy"; return 1; fi
+  if [ "${dirty_n:-0}" -ne 0 ]; then echo "$dirty_n uncommitted file(s)";     return 1; fi
+  if [ "$in_use" = yes ];   then echo "a live session is in it";              return 1; fi
+  if [ "$pr_state" != MERGED ]; then echo "PR state '${pr_state:-none}', not MERGED"; return 1; fi
+  echo ok
+}
+
+if [ -n "${GC_WORKTREES_LIB_ONLY:-}" ]; then
+  return 0 2>/dev/null || exit 0
+fi
+
+# ---------------------------------------------------------------------------
+live_cwds() {
+  # A session that is inside a worktree is the case worth being careful about;
+  # missing registry files simply mean no sessions, not an error.
+  jq -r 'select(.status!=null) | .cwd' "$SESSIONS_DIR"/*.json 2>/dev/null | sort -u
+}
+
+LIVE="$(live_cwds)"
+removed=0 skipped=0 freed=0
+
+for repo in "$ROOT"/*/; do
+  repo="${repo%/}"; [ -d "$repo/.git" ] || continue
+  slug="$(git -C "$repo" remote get-url origin 2>/dev/null \
+          | sed -E 's#.*github.com[:/]##; s#\.git$##')" || continue
+  [ -n "$slug" ] || continue
+
+  # `worktree list` reports the main checkout first — never a candidate.
+  while read -r wt; do
+    [ -n "$wt" ] && [ -e "$wt" ] || continue
+    branch="$(git -C "$wt" symbolic-ref --quiet --short HEAD)" || continue
+
+    # "Pushed" means an upstream is CONFIGURED, not that it still resolves.
+    # After a squash-merge GitHub deletes the remote branch and `fetch --prune`
+    # drops the tracking ref, leaving branch.<n>.merge pointing at nothing — so
+    # a resolvable upstream means the branch is still open, and an unresolvable
+    # one is the signal we are looking for. (Same distinction stranded-work.sh
+    # turns on; getting it backwards there reported 24 merged PRs as stranded.)
+    upstream="$(git -C "$wt" for-each-ref --format='%(upstream:short)' "refs/heads/$branch")"
+    [ -n "$upstream" ] && pushed=yes || pushed=no
+    if [ "$pushed" = yes ] && \
+       git -C "$wt" rev-parse --verify -q "refs/remotes/$upstream" >/dev/null 2>&1; then
+      continue   # remote branch still exists — the PR is open, leave it alone
+    fi
+
+    dirty_n="$(git -C "$wt" status --porcelain 2>/dev/null | wc -l)"
+    printf '%s\n' "$LIVE" | grep -qxF "$wt" && in_use=yes || in_use=no
+
+    pr_state=""
+    if [ "$pushed" = yes ] && [ "$dirty_n" -eq 0 ] && [ "$in_use" = no ]; then
+      # Only ask GitHub once the cheap local checks have passed — this is the
+      # only network call, and it is the authority, re-asked at removal time
+      # rather than trusted from an earlier scan.
+      pr_state="$(gh pr list -R "$slug" --head "$branch" --state all \
+                  --json state --jq '.[0].state' 2>/dev/null)"
+    fi
+
+    reason="$(safe_to_remove "$pushed" "$dirty_n" "$in_use" "$pr_state")"
+    if [ "$reason" != ok ]; then
+      printf 'keep    %-52s %s\n' "${wt#"$ROOT"/}" "$reason"
+      skipped=$((skipped + 1))
+      continue
+    fi
+
+    mb="$(du -sm "$wt" 2>/dev/null | cut -f1)"
+    if [ "$GO" -eq 1 ]; then
+      if git -C "$repo" worktree remove --force "$wt" 2>/dev/null; then
+        git -C "$repo" branch -D "$branch" >/dev/null 2>&1
+        printf 'removed %-52s %sMB  (%s)\n' "${wt#"$ROOT"/}" "$mb" "$branch"
+        removed=$((removed + 1)); freed=$((freed + mb))
+      else
+        printf 'FAILED  %-52s could not remove\n' "${wt#"$ROOT"/}"
+        skipped=$((skipped + 1))
+      fi
+    else
+      printf 'would   %-52s %sMB  (%s)\n' "${wt#"$ROOT"/}" "$mb" "$branch"
+      removed=$((removed + 1)); freed=$((freed + mb))
+    fi
+  done < <(git -C "$repo" worktree list --porcelain 2>/dev/null \
+           | awk '/^worktree /{print $2}' | tail -n +2)
+done
+
+echo "---"
+if [ "$GO" -eq 1 ]; then
+  echo "removed $removed worktrees, ${freed}MB freed; $skipped kept"
+else
+  echo "$removed removable (${freed}MB), $skipped kept — rerun with --go to remove"
+fi
diff --git a/scripts/fleet/test-gc-merged-worktrees.sh b/scripts/fleet/test-gc-merged-worktrees.sh
new file mode 100755
index 0000000..c7d7e85
--- /dev/null
+++ b/scripts/fleet/test-gc-merged-worktrees.sh
@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+#
+# Tests for the worktree GC predicate.
+#
+# This script deletes checkouts, so the only interesting failure mode is a FALSE
+# POSITIVE: removing something that was not safe. Every refusal below is a case
+# that would have destroyed work, so each is tested individually rather than
+# through one combined "unsafe" fixture — a single guard silently inverting is
+# exactly what a combined test hides.
+#
+# The predicate is pure by design so all of this runs without a GitHub repo, a
+# network call, or a live agent session.
+
+set -uo pipefail
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+SCRIPT="$HERE/gc-merged-worktrees.sh"
+
+PASS=0
+FAIL=0
+ok() { printf '  ✓ %s\n' "$1"; PASS=$((PASS + 1)); }
+no() { printf '  ✗ %s\n' "$1"; FAIL=$((FAIL + 1)); }
+
+export GC_WORKTREES_LIB_ONLY=1
+# shellcheck source=/dev/null
+source "$SCRIPT" ""
+unset GC_WORKTREES_LIB_ONLY
+
+# safe_to_remove <pushed> <dirty_n> <in_use> <pr_state>
+say() { safe_to_remove "$@"; }
+
+echo "the one case that may be removed:"
+
+out="$(say yes 0 no MERGED)"; rc=$?
+[ $rc -eq 0 ] && [ "$out" = ok ] \
+  && ok "pushed + clean + unused + MERGED is removable" \
+  || no "the happy path must return ok (rc=$rc, out='$out')"
+
+echo
+echo "every refusal — each of these would have destroyed work:"
+
+# The one that matters most. A branch with no upstream exists on exactly one
+# disk; this is the case the whole guard exists to protect.
+out="$(say no 0 no MERGED)"; rc=$?
+[ $rc -ne 0 ] && [[ "$out" == *"only copy"* ]] \
+  && ok "never-pushed is refused even when everything else looks fine" \
+  || no "unpushed work must never be removable (rc=$rc, out='$out')"
+
+out="$(say yes 1 no MERGED)"; rc=$?
+[ $rc -ne 0 ] && [[ "$out" == *"uncommitted"* ]] \
+  && ok "a single uncommitted file is enough to refuse" \
+  || no "dirty worktrees must be refused (rc=$rc, out='$out')"
+
+out="$(say yes 0 yes MERGED)"; rc=$?
+[ $rc -ne 0 ] && [[ "$out" == *"live session"* ]] \
+  && ok "a worktree with a live session in it is refused" \
+  || no "in-use worktrees must be refused (rc=$rc, out='$out')"
+
+# CLOSED is not MERGED. An abandoned PR is still a decision someone may want to
+# revisit, and the branch content exists nowhere else once the remote is gone.
+out="$(say yes 0 no CLOSED)"; rc=$?
+[ $rc -ne 0 ] && [[ "$out" == *"CLOSED"* ]] \
+  && ok "a CLOSED (abandoned) PR is refused — closed is not merged" \
+  || no "CLOSED must be refused (rc=$rc, out='$out')"
+
+out="$(say yes 0 no OPEN)"; rc=$?
+[ $rc -ne 0 ] \
+  && ok "an OPEN PR is refused" \
+  || no "OPEN must be refused (rc=$rc, out='$out')"
+
+# `gh` returning nothing is ambiguous — no PR, no auth, rate limit, network
+# down. Ambiguity must resolve to "keep", never to "delete".
+out="$(say yes 0 no "")"; rc=$?
+[ $rc -ne 0 ] && [[ "$out" == *"none"* ]] \
+  && ok "an empty gh answer keeps the worktree — ambiguity is not consent" \
+  || no "empty PR state must be refused (rc=$rc, out='$out')"
+
+echo
+echo "the script itself:"
+
+out="$(bash "$SCRIPT" --nonsense 2>&1)"; rc=$?
+[ $rc -eq 2 ] \
+  && ok "an unknown argument fails loudly rather than defaulting to --go" \
+  || no "unknown args must exit 2 (rc=$rc)"
+
+# Default must be dry-run. If this ever inverts, the first person to run the
+# script with no arguments loses 5 GB of checkouts.
+out="$(FLEET_ROOT="$(mktemp -d)" bash "$SCRIPT" 2>&1)"; rc=$?
+[[ "$out" == *"rerun with --go"* ]] \
+  && ok "no arguments means dry-run, and says so" \
+  || no "the default must be dry-run (out='$out')"
+
+echo
+printf '  %d passed, %d failed\n' "$PASS" "$FAIL"
+[ "$FAIL" -eq 0 ]