diff --git a/tools/install.sh b/tools/install.sh
index d6db3f28..f6a29833 100755
--- a/tools/install.sh
+++ b/tools/install.sh
@@ -309,52 +309,84 @@ require_cmd() {
   fi
 }
 
-# Persist $PREFIX/bin on PATH instead of only warning about it.
+# True if any shell rc file already puts $1 on PATH.
 #
-# The warning it replaces was the last step of an otherwise successful install,
-# so the installer reported success and left `mosaic: command not found` — an
-# unattended install had no operator to read the advice and act on it.
+# Each file is tested for existence first and grepped one at a time, rather than
+# handed to a single `grep -qs ... "${rc_files[@]}"`. Handing grep a missing file
+# makes the exit status implementation-defined: GNU grep 3.11 returns 0 when -q
+# matched an earlier file, ugrep 7.5 returns 2 for the missing one regardless.
+# On the 2 path the caller reads "not present yet" and appends a duplicate PATH
+# line on every single install.
+path_entry_exists() {
+  local dir="$1" rc_file
+  for rc_file in "$HOME/.profile" "$HOME/.zshenv" "$HOME/.zshrc" "$HOME/.bashrc"; do
+    if [[ -f "$rc_file" ]] && grep -qF "$dir" "$rc_file"; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+# Append `export PATH="$1:$PATH"` to the shell profile so $1 survives this
+# process. An `export` here reaches only the installer; every directory the
+# install leaves behind has to be written down somewhere a later shell reads.
 #
 # Deliberately NOT ~/.bashrc: Debian's default .bashrc returns early for
 # non-interactive shells, so a PATH line appended to the bottom of it is
 # unreachable to `bash -lc`, to systemd units, and to every agent seat — the
-# exact consumers that need the CLI. ~/.profile is read by login shells and
-# Debian's .profile sources .bashrc for interactive ones, so a single line there
-# reaches both. For zsh the always-sourced file is .zshenv, not .zshrc.
-ensure_prefix_on_path() {
-  if [[ ":$PATH:" == *":$PREFIX/bin:"* ]]; then
-    return
+# exact consumers that need these binaries. ~/.profile is read by login shells
+# and Debian's .profile sources .bashrc for interactive ones, so a single line
+# there reaches both. For zsh the always-sourced file is .zshenv, not .zshrc.
+#
+# $1 = directory to add, $2 = label for the comment line.
+# Returns 1 (having warned) if the profile could not be written.
+persist_on_path() {
+  local dir="$1" label="$2" profile
+
+  if path_entry_exists "$dir"; then
+    return 0
   fi
 
-  local profile rc_files=("$HOME/.profile" "$HOME/.zshenv" "$HOME/.zshrc" "$HOME/.bashrc")
   if [[ -n "${ZSH_VERSION:-}" ]] || [[ "$(basename "${SHELL:-}")" == "zsh" ]]; then
     profile="$HOME/.zshenv"
   else
     profile="$HOME/.profile"
   fi
 
-  if grep -qslF "$PREFIX/bin" "${rc_files[@]}" 2>/dev/null; then
-    warn "$PREFIX/bin is in your shell profile but not in this shell"
-    dim "  Run:  export PATH=\"$PREFIX/bin:\$PATH\"   (or start a new login shell)"
-    return
-  fi
-
   # Probe writability in a subshell. A redirection failure on a special built-in
   # aborts the shell it runs in, so it has to be a child; and the redirection on
   # the subshell is what silences the "Permission denied" the shell would
   # otherwise print ahead of our own message.
   if ! ( : >>"$profile" ) 2>/dev/null; then
-    warn "$PREFIX/bin is not on your PATH and $profile could not be written"
-    dim "  Add to your shell rc:  export PATH=\"$PREFIX/bin:\$PATH\""
-    return
+    warn "$dir is not on your PATH and $profile could not be written"
+    dim "  Add to your shell rc:  export PATH=\"$dir:\$PATH\""
+    return 1
   fi
 
   {
     echo ""
-    echo "# Mosaic CLI"
-    echo "export PATH=\"$PREFIX/bin:\$PATH\""
+    echo "# $label"
+    echo "export PATH=\"$dir:\$PATH\""
   } >>"$profile"
-  ok "Added $PREFIX/bin to PATH in $profile"
+  ok "Added $dir to PATH in $profile"
+  return 0
+}
+
+# Persist $PREFIX/bin on PATH instead of only warning about it.
+#
+# The warning it replaces was the last step of an otherwise successful install,
+# so the installer reported success and left `mosaic: command not found` — an
+# unattended install had no operator to read the advice and act on it.
+ensure_prefix_on_path() {
+  if [[ ":$PATH:" == *":$PREFIX/bin:"* ]]; then
+    return
+  fi
+
+  if path_entry_exists "$PREFIX/bin"; then
+    warn "$PREFIX/bin is in your shell profile but not in this shell"
+  elif ! persist_on_path "$PREFIX/bin" "Mosaic CLI"; then
+    return
+  fi
   dim "  Run:  export PATH=\"$PREFIX/bin:\$PATH\"   (or start a new login shell)"
 }
 
@@ -670,6 +702,16 @@ install_node() {
   return 0
 }
 
+# Make the Mosaic-managed Node reachable from the next shell as well as this
+# one. Measured on a greenfield canary run: without this the install finished
+# rc=0, wrote $PREFIX/bin to ~/.profile, and the next login shell found `mosaic`
+# and then died on `env: 'node': No such file or directory` — the CLI is a Node
+# script, so a CLI on PATH without its runtime is a successful install that
+# produces a broken command.
+persist_node_on_path() {
+  persist_on_path "$NODE_ROOT/current/bin" "Mosaic-managed Node.js" || true
+}
+
 ensure_node() {
   if command -v node &>/dev/null && node_is_suitable node; then
     return 0
@@ -678,6 +720,7 @@ ensure_node() {
   # A previous run may have installed one that is not on this shell's PATH.
   if node_is_suitable "$NODE_ROOT/current/bin/node"; then
     export PATH="$NODE_ROOT/current/bin:$PATH"
+    persist_node_on_path
     return 0
   fi
 
@@ -705,6 +748,7 @@ ensure_node() {
     fail "Could not bootstrap Node.js. Install Node.js >= $NODE_MIN_MAJOR and re-run."
     exit 1
   fi
+  persist_node_on_path
 }
 
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