test(fleet): name what the pane-boundary case's binary check rides on (#1241)

Review finding from scooby. This case does not use run_start, so
install_pane_binaries' symlinks land under a home its launcher never consults
(HOME is the trusted parent here). It resolves mosaic and pi through
MOSAIC_RUNTIME_BIN=$FAKE_BIN instead. Valid path, valid green — and a trap for
anyone who later drops that env var believing the symlinks cover it, which
would break the #1241 binary check rather than exercise it.

Comment only; no behavior change. Harness rc=0.

Refs #1241.

packages/mosaic/__tests__/platform/detect.test.ts

@@ -1,74 +0,0 @@
-import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
-
-// homedir/platform are read at call time, so they can be stubbed per case.
-vi.mock('node:os', async (importOriginal) => {
-  const actual = await importOriginal<typeof import('node:os')>();
-  return {
-    ...actual,
-    homedir: () => '/home/tester',
-    platform: () => mockPlatform,
-  };
-});
-
-let mockPlatform: NodeJS.Platform = 'linux';
-
-const { getShellProfilePath, detectShell } = await import('../../src/platform/detect.js');
-
-describe('getShellProfilePath', () => {
-  const originalShell = process.env['SHELL'];
-  const originalZdotdir = process.env['ZDOTDIR'];
-
-  beforeEach(() => {
-    mockPlatform = 'linux';
-    delete process.env['ZDOTDIR'];
-  });
-
-  afterEach(() => {
-    if (originalShell === undefined) delete process.env['SHELL'];
-    else process.env['SHELL'] = originalShell;
-    if (originalZdotdir === undefined) delete process.env['ZDOTDIR'];
-    else process.env['ZDOTDIR'] = originalZdotdir;
-  });
-
-  // The regression this guards: setupPath() in stages/finalize.ts appends the
-  // PATH export to whatever this returns. A line written to ~/.bashrc is
-  // unreachable to `bash -lc`, systemd units and agent seats, because Debian's
-  // default .bashrc returns early for non-interactive shells — so an install
-  // reported success and left `mosaic: command not found`. Same for .zshrc,
-  // which zsh only reads for interactive shells.
-  it('never targets an interactive-only rc file', () => {
-    for (const shell of ['/bin/bash', '/usr/bin/zsh']) {
-      process.env['SHELL'] = shell;
-      const profile = getShellProfilePath();
-      expect(profile).not.toMatch(/\.bashrc$/);
-      expect(profile).not.toMatch(/\.zshrc$/);
-    }
-  });
-
-  it('uses ~/.profile for bash', () => {
-    process.env['SHELL'] = '/bin/bash';
-    expect(getShellProfilePath()).toBe('/home/tester/.profile');
-  });
-
-  it('uses ~/.zshenv for zsh', () => {
-    process.env['SHELL'] = '/usr/bin/zsh';
-    expect(getShellProfilePath()).toBe('/home/tester/.zshenv');
-  });
-
-  it('honours ZDOTDIR for zsh', () => {
-    process.env['SHELL'] = '/usr/bin/zsh';
-    process.env['ZDOTDIR'] = '/custom/zdot';
-    expect(getShellProfilePath()).toBe('/custom/zdot/.zshenv');
-  });
-
-  it('falls back to ~/.profile for an unknown shell', () => {
-    process.env['SHELL'] = '/bin/somethingelse';
-    expect(detectShell()).toBe('unknown');
-    expect(getShellProfilePath()).toBe('/home/tester/.profile');
-  });
-
-  it('still routes fish to its own config', () => {
-    process.env['SHELL'] = '/usr/bin/fish';
-    expect(getShellProfilePath()).toBe('/home/tester/.config/fish/config.fish');
-  });
-});

packages/mosaic/framework/systemd/user/test-fleet-units.sh

@@ -128,6 +128,14 @@ EOF
 sleep 30
 EOF
   chmod 700 "$AGENT_BIN/mosaic"
+  # The launcher resolves the roster's runtime against PANE_PATH before it
+  # spawns anything (#1241), so the runtime this projection names has to be
+  # present here even though the fake `mosaic` above never execs it.
+  cat > "$AGENT_BIN/pi" <<'EOF'
+#!/bin/sh
+sleep 30
+EOF
+  chmod 700 "$AGENT_BIN/pi"
   server_environment_before=$(tmux -L "$TEST_SOCKET" show-environment -g | sort)
   server_sessions_before=$(tmux -L "$TEST_SOCKET" list-sessions | sort)
   if /usr/bin/env -i HOME="$HOLDER_HOME" PATH=/usr/bin:/bin MOSAIC_HOME="$AGENT_HOME" \

packages/mosaic/framework/tools/fleet/start-agent-session.sh

@@ -286,6 +286,36 @@ _build_runtime_bin_prefix() {
 MOSAIC_RUNTIME_BIN_PREFIX=$(_build_runtime_bin_prefix)
 PANE_PATH=${MOSAIC_RUNTIME_BIN_PREFIX:+${MOSAIC_RUNTIME_BIN_PREFIX}:}/usr/local/bin:/usr/bin:/bin
 
+# #1241. The pane runs `mosaic yolo <runtime>` under PANE_PATH with a cleared
+# environment. A binary missing from *that* path is a pane that dies in under a
+# second, inside a session nobody is attached to, with its diagnostic scrolled
+# into a pane tmux then destroys. Resolve both here, before any effect, where
+# the failure is still attributable to the thing that caused it.
+#
+# `mosaic yolo <runtime>` runs checkRuntime(runtime) and the binary it looks for
+# is named exactly like the runtime, so resolving the runtime name is the same
+# question the pane will ask a moment later — asked while an operator can still
+# see the answer.
+_resolve_in_pane_path() {
+  PATH="$PANE_PATH" command -v -- "$1" 2>/dev/null
+}
+
+# Exit 69 (EX_UNAVAILABLE): the seat cannot be provided. Distinguished from the
+# 64 (EX_USAGE) rejections above, which mean the projection itself was bad —
+# here the data is fine and the host is not ready. Callers tell the individual
+# cases apart by `code=`, the same way fail_env's many codes share exit 64.
+fail_launch() {
+  local code="$1"
+  shift
+  echo "ERROR: agent launch aborted: code=${code} agent=${AGENT_NAME} $*" >&2
+  exit 69
+}
+
+for required_binary in mosaic "$MOSAIC_AGENT_RUNTIME"; do
+  _resolve_in_pane_path "$required_binary" >/dev/null ||
+    fail_launch missing-binary "'${required_binary}' is not on the pane PATH (${PANE_PATH})"
+done
+
 _ensure_claude_workdir_trusted() {
   local workdir="$1"
   local resolved
@@ -384,6 +414,19 @@ if [ -n "$PANE_PID" ]; then
   _start_heartbeat_sidecar "$AGENT_NAME" "$PANE_PID" \
     "$MOSAIC_HEARTBEAT_RUN_DIR" "$MOSAIC_HEARTBEAT_INTERVAL" || \
     echo "WARNING: heartbeat sidecar could not be started for $AGENT_NAME" >&2
+elif _tmux has-session -t "=${AGENT_NAME}:0.0" 2>/dev/null; then
+  # #1241. Session present, no pane PID after a second of retries. Whatever this
+  # is, it is not a seat an operator can use, so it is not a success either.
+  fail_launch pane-pid-unresolved \
+    "tmux reports the session but no pane PID after 5 attempts"
 else
-  echo "WARNING: could not resolve pane PID for $AGENT_NAME — heartbeat sidecar not started" >&2
+  # #1241. This branch used to print a WARNING about the heartbeat sidecar and
+  # exit 0. It is not a heartbeat problem: tmux destroys a session when its pane
+  # command exits, so an absent session one second after new-session means the
+  # runtime died on startup. Reporting it as success is what let `fleet start`
+  # return 0 over three dead panes — the launcher knew, and said the wrong thing
+  # at the wrong severity to the wrong layer.
+  fail_launch pane-did-not-survive \
+    "the pane exited immediately and tmux destroyed the session;" \
+    "run 'mosaic yolo ${MOSAIC_AGENT_RUNTIME}' in ${MOSAIC_AGENT_WORKDIR} to see why"
 fi

packages/mosaic/framework/tools/fleet/test-start-agent-session.sh

@@ -23,8 +23,26 @@ index=0
 if [ "${args[0]:-}" = -L ]; then index=2; fi
 case "${args[$index]:-}" in
   has-session)
+    # The holder always answers. MOSAIC_TEST_HELD_SESSIONS lets a case add
+    # other targets that should answer too — without it there is no way to
+    # model "tmux still reports the session" for a non-holder agent, and the
+    # launcher's pane-pid-unresolved branch is unreachable from this harness.
+    #
+    # A listed target answers only AFTER new-session, because the launcher asks
+    # this question twice about the same name: once before launching, where a
+    # yes means "already running, nothing to do, exit 0", and once after, where
+    # a yes means "the session survived". A shim that answered yes to both
+    # would short-circuit at the first and never reach the branch under test —
+    # it would look like coverage and measure the idempotency path instead.
     for argument in "${args[@]}"; do
       [ "$argument" = '=_holder:0.0' ] && exit 0
+      case " ${MOSAIC_TEST_HELD_SESSIONS:-} " in
+        *" $argument "*)
+          if tr '\0' '\n' < "${MOSAIC_TEST_TMUX_CALLS:?}" | grep -qxF new-session; then
+            exit 0
+          fi
+          ;;
+      esac
     done
     exit 1
     ;;
@@ -62,6 +80,30 @@ env -0 > "${MOSAIC_HOME:?}/fleet/pane-environment"
 SHIM
 chmod +x "$FAKE_BIN/mosaic"
 
+# The runtime the rosters below name. The launcher resolves it against PANE_PATH
+# before spawning (#1241), so it has to exist somewhere the pane would find it —
+# not merely on the launcher's own PATH.
+printf '#!/usr/bin/env bash\nexit 0\n' > "$FAKE_BIN/pi"
+chmod +x "$FAKE_BIN/pi"
+
+# PANE_PATH is derived partly from `npm config get prefix`. Left to the real npm
+# it would splice whatever the host has installed into the path under test, and
+# the missing-binary cases below would pass or fail by accident of the machine.
+cat > "$FAKE_BIN/npm" <<'SHIM'
+#!/usr/bin/env bash
+printf '%s\n' "${MOSAIC_TEST_NPM_PREFIX:-/nonexistent}"
+SHIM
+chmod +x "$FAKE_BIN/npm"
+
+# PANE_PATH always ends in the system path. A host that installs these there can
+# not measure the missing-binary cases at all, and a green run would mean
+# nothing — so say so instead of passing.
+for host_binary in mosaic pi; do
+  if PATH=/usr/local/bin:/usr/bin:/bin command -v "$host_binary" >/dev/null 2>&1; then
+    fail "host provides '$host_binary' in the system path; missing-binary cases are not measurable here"
+  fi
+done
+
 write_generated() {
   local home="$1"
   local agent="$2"
@@ -81,6 +123,19 @@ MOSAIC_TMUX_SOCKET=mosaic-test
 EOF
   chmod 600 "$home/fleet/agents/$agent.env.generated"
   mkdir -p "$home/work"
+  install_pane_binaries "$home"
+}
+
+# `$PANE_HOME/.npm-global/bin` is one of the prefixes the launcher folds into
+# PANE_PATH, so this is the pane's own view of "installed", distinct from the
+# launcher's PATH. Tests that need a binary *absent* remove it from here.
+install_pane_binaries() {
+  local pane_home="$1"
+  mkdir -p "$pane_home/.npm-global/bin"
+  local binary
+  for binary in mosaic pi; do
+    ln -sf "$FAKE_BIN/$binary" "$pane_home/.npm-global/bin/$binary"
+  done
 }
 
 run_start() {
@@ -88,6 +143,7 @@ run_start() {
   local agent="$2"
   HOME="$home" PATH="$FAKE_BIN:$PATH" MOSAIC_TEST_TMUX_CALLS="$TMUX_CALLS" \
     MOSAIC_TEST_PANE_PID="${MOSAIC_TEST_PANE_PID:-}" \
+    MOSAIC_TEST_HELD_SESSIONS="${MOSAIC_TEST_HELD_SESSIONS:-}" \
     MOSAIC_TEST_HOME="$home" \
     MOSAIC_TEST_FLEET_OWNER=123e4567-e89b-12d3-a456-426614174000 \
     MOSAIC_HOME="$home" "$START" "$agent"
@@ -98,7 +154,10 @@ run_start() {
 HOME_VALID="$ROOT/valid"
 AGENT_VALID="coder0"
 write_generated "$HOME_VALID" "$AGENT_VALID"
-run_start "$HOME_VALID" "$AGENT_VALID"
+# A live pane PID is part of what "valid launch" means. Until #1241 this case
+# ran with none, so the suite's one success path was itself a dead pane the
+# launcher reported as fine.
+MOSAIC_TEST_PANE_PID=$$ run_start "$HOME_VALID" "$AGENT_VALID"
 valid_args=$(tr '\0' '\n' < "$TMUX_CALLS")
 echo "$valid_args" | grep -qF new-session || fail "valid generated projection did not reach tmux"
 echo "$valid_args" | grep -qF 'mosaic' || fail "fixed mosaic launcher command missing"
@@ -245,6 +304,13 @@ PANE_BASH_ENV="$ROOT/pane-boundary.bash-env"
 printf 'MOSAIC_RUNTIME_BIN=%s\n' "$FAKE_BIN" > \
   "$HOME_PANE_BOUNDARY/fleet/agents/coder-pane-boundary.env.local"
 chmod 600 "$HOME_PANE_BOUNDARY/fleet/agents/coder-pane-boundary.env.local"
+# This case does not go through run_start, so its pane binaries come from
+# MOSAIC_RUNTIME_BIN=$FAKE_BIN in the env.local written above — not from the
+# symlinks install_pane_binaries planted under the generated home, which this
+# launcher never consults because HOME here is the trusted parent. That is a
+# legitimate resolution path, but it means dropping MOSAIC_RUNTIME_BIN from
+# this case on the belief that the symlinks cover it would break the #1241
+# binary check rather than exercise it.
 LD_PRELOAD='/not/loaded/by-clean-bootstrap.so' \
 BASH_ENV="$PANE_BASH_ENV" \
 MOSAIC_UNTRUSTED_SENTINEL='must-not-reach-pane' \
@@ -258,6 +324,7 @@ PATH="$PANE_STALE_PATH" \
     "MOSAIC_TEST_HOME=$PANE_TRUSTED_HOME" \
     MOSAIC_TEST_FLEET_OWNER=123e4567-e89b-12d3-a456-426614174000 \
     MOSAIC_TEST_EXECUTE_PANE=1 \
+    "MOSAIC_TEST_PANE_PID=$$" \
     "$START" coder-pane-boundary
 pane_args=$(tr '\0' '\n' < "$TMUX_CALLS")
 echo "$pane_args" | grep -qxF "HOME=$PANE_TRUSTED_HOME" || \
@@ -392,6 +459,75 @@ echo "$interaction_policy_args" | grep -qF 'new-session' && \
 echo "$output" | grep -qF 'operator interaction service requires runtime pi' || \
   fail "interaction pinned-policy check did not follow strict parsing"
 
+# #1241. The pane runs `mosaic yolo <runtime>` against PANE_PATH. A binary
+# missing from that path is a launch failure, and it has to be named before the
+# session is created — after it, the diagnostic dies with the pane.
+assert_missing_pane_binary_rejected() {
+  local binary="$1"
+  local home="$ROOT/missing-$binary"
+  local agent="coder-missing-$binary"
+  write_generated "$home" "$agent"
+  rm -f "$home/.npm-global/bin/$binary"
+
+  : > "$TMUX_CALLS"
+  local output
+  if output=$(MOSAIC_TEST_PANE_PID=$$ run_start "$home" "$agent" 2>&1); then
+    fail "launch succeeded with '$binary' absent from the pane PATH"
+  fi
+  echo "$output" | grep -qF 'code=missing-binary' || fail "missing '$binary' diagnostic missing"
+  echo "$output" | grep -qF "'$binary'" || fail "missing-binary diagnostic did not name $binary"
+  if tr '\0' '\n' < "$TMUX_CALLS" | grep -qF new-session; then
+    fail "launcher created a session it knew would die ($binary absent)"
+  fi
+}
+
+assert_missing_pane_binary_rejected mosaic
+assert_missing_pane_binary_rejected pi
+
+# #1241. tmux destroys a session when its pane command exits, so no pane PID a
+# second after new-session means the runtime died on startup. This used to be a
+# WARNING about the heartbeat sidecar followed by exit 0 — three layers above it
+# then reported a fleet that was not running.
+: > "$TMUX_CALLS"
+HOME_DEAD_PANE="$ROOT/dead-pane"
+write_generated "$HOME_DEAD_PANE" "coder-dead-pane"
+if output=$(MOSAIC_TEST_PANE_PID='' run_start "$HOME_DEAD_PANE" coder-dead-pane 2>&1); then
+  fail "launcher reported success over a pane that did not survive"
+fi
+echo "$output" | grep -qF 'code=pane-did-not-survive' || fail "dead-pane diagnostic missing"
+if echo "$output" | grep -qiF 'heartbeat'; then
+  fail "dead pane is still being reported as a heartbeat-sidecar problem"
+fi
+tr '\0' '\n' < "$TMUX_CALLS" | grep -qF new-session || \
+  fail "dead-pane case did not reach the launch it is measuring"
+
+# #1241, the other way a pane fails. Above, tmux destroyed the session and
+# has-session said so. Here the session is still there and no PID comes back
+# after the retries — a different fault (the pane is alive but unusable, or
+# tmux is answering inconsistently) that an operator has to be told apart from
+# a runtime that died on startup.
+#
+# This case exists because the branch that handles it shipped with nothing able
+# to reach it: the shim answered has-session only for the holder, so every
+# non-holder agent landed in the session-is-gone branch no matter what. A
+# defensive branch nothing exercises is the same shape as the bug this whole
+# change is about, one layer down.
+: > "$TMUX_CALLS"
+HOME_NO_PID="$ROOT/pane-no-pid"
+write_generated "$HOME_NO_PID" "coder-no-pid"
+if output=$(MOSAIC_TEST_PANE_PID='' MOSAIC_TEST_HELD_SESSIONS='=coder-no-pid:0.0' \
+  run_start "$HOME_NO_PID" coder-no-pid 2>&1); then
+  fail "launcher reported success over a session with no resolvable pane PID"
+fi
+echo "$output" | grep -qF 'code=pane-pid-unresolved' || \
+  fail "session-present/no-PID was not reported as pane-pid-unresolved: $output"
+if echo "$output" | grep -qF 'code=pane-did-not-survive'; then
+  fail "a session tmux still reports was diagnosed as a destroyed session"
+fi
+if echo "$output" | grep -qiF 'heartbeat'; then
+  fail "an unresolvable pane PID is still being reported as a heartbeat-sidecar problem"
+fi
+
 # Exact stop derives the socket exclusively from the validated generated
 # projection and ignores an ambient socket supplied by the caller.
 : > "$TMUX_CALLS"

packages/mosaic/src/platform/detect.ts

@@ -1,3 +1,4 @@
+import { existsSync } from 'node:fs';
 import { join } from 'node:path';
 import { homedir, platform } from 'node:os';
 
@@ -21,18 +22,15 @@ export function getShellProfilePath(): string | null {
 
   const shell = detectShell();
   switch (shell) {
-    // Both of these deliberately avoid the interactive-only rc files.
-    // Debian's default .bashrc returns early for non-interactive shells, so a
-    // PATH line appended to it never runs for `bash -lc`, systemd units, or
-    // agent seats — an install could report success and still leave `mosaic`
-    // unreachable. .profile is read by login shells and sources .bashrc for
-    // interactive ones, so one line covers both; .zshenv is zsh's equivalent.
     case 'zsh': {
       const zdotdir = process.env['ZDOTDIR'] ?? home;
-      return join(zdotdir, '.zshenv');
+      return join(zdotdir, '.zshrc');
     }
-    case 'bash':
+    case 'bash': {
+      const bashrc = join(home, '.bashrc');
+      if (existsSync(bashrc)) return bashrc;
       return join(home, '.profile');
+    }
     case 'fish':
       return join(home, '.config', 'fish', 'config.fish');
     default:

tools/install.sh

@@ -309,87 +309,6 @@ require_cmd() {
   fi
 }
 
-# True if any shell rc file already puts $1 on PATH.
-#
-# Each file is tested for existence first and grepped one at a time, rather than
-# handed to a single `grep -qs ... "${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 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
-
-  if [[ -n "${ZSH_VERSION:-}" ]] || [[ "$(basename "${SHELL:-}")" == "zsh" ]]; then
-    profile="$HOME/.zshenv"
-  else
-    profile="$HOME/.profile"
-  fi
-
-  # Probe writability in a subshell. A redirection failure on a special built-in
-  # aborts the shell it runs in, so it has to be a child; and the redirection on
-  # the subshell is what silences the "Permission denied" the shell would
-  # otherwise print ahead of our own message.
-  if ! ( : >>"$profile" ) 2>/dev/null; then
-    warn "$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 "# $label"
-    echo "export PATH=\"$dir:\$PATH\""
-  } >>"$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=\"$PREFIX/bin:\$PATH\"   (or start a new login shell)"
-}
-
 installed_cli_version() {
   local json
   json="$(npm ls -g --depth=0 --json --prefix="$PREFIX" 2>/dev/null)" || true
@@ -597,175 +516,8 @@ install_next_cli_from_registry() {
   ok "Installed @next packages: CLI ${installed_cli}, gateway ${installed_gateway}"
 }
 
-# ─── node bootstrap ───────────────────────────────────────────────────────────
-#
-# Nothing on a greenfield host installs Node.js, yet this installer and the CLI
-# it installs both hard-require it. Measured on a clean Debian 13 image: the
-# installer stopped at `require_cmd node` with "Required command not found" and
-# nothing was installed, with no hint of how to proceed.
-#
-# Inlined rather than factored into a sibling file on purpose: this script is
-# fetched standalone by curl and has nothing to source.
-#
-# No-op when a suitable node is already on PATH, so it never fights an
-# operator's nvm/fnm/distro node.
-
-NODE_ROOT="${MOSAIC_NODE_ROOT:-$HOME/.mosaic/node}"
-NODE_BOOTSTRAP_VERSION="${MOSAIC_NODE_VERSION:-v22.23.2}"
-NODE_MIN_MAJOR="${MOSAIC_NODE_MIN_MAJOR:-20}"
-NODE_DIST_BASE="${MOSAIC_NODE_DIST_BASE:-https://nodejs.org/dist}"
-
-# Major version of the node at $1, or empty if it will not run.
-node_major_of() {
-  local candidate="$1" version
-  version="$("$candidate" -e 'process.stdout.write(process.versions.node)' 2>/dev/null)" || return 0
-  printf '%s' "${version%%.*}"
-}
-
-node_is_suitable() {
-  local major
-  major="$(node_major_of "$1")"
-  [[ -n "$major" ]] && [[ "$major" -ge "$NODE_MIN_MAJOR" ]]
-}
-
-install_node() {
-  local node_os node_arch tarball release_url work_dir extracted target node_bin
-
-  case "$(uname -s)" in
-    Linux)  node_os="linux" ;;
-    Darwin) node_os="darwin" ;;
-    *) fail "Unsupported OS '$(uname -s)'. Install Node.js >= $NODE_MIN_MAJOR manually."; return 1 ;;
-  esac
-
-  # Linux here means glibc. Node's official linux-x64 build is dynamically
-  # linked against glibc, so on musl (Alpine) the binary will not exec — but it
-  # fails visibly: node_is_suitable rejects it and ensure_node exits with
-  # "install Node.js manually". No silent breakage, just a wasted download.
-  # A musl host needs the unofficial build, which is out of scope here.
-  case "$(uname -m)" in
-    x86_64|amd64)  node_arch="x64" ;;
-    aarch64|arm64) node_arch="arm64" ;;
-    armv7l)        node_arch="armv7l" ;;
-    *) fail "Unsupported architecture '$(uname -m)'. Install Node.js >= $NODE_MIN_MAJOR manually."; return 1 ;;
-  esac
-
-  # .tar.gz rather than the smaller .tar.xz: gzip is universally present, xz is
-  # not, and a minimal image is exactly the case this exists to handle.
-  tarball="node-${NODE_BOOTSTRAP_VERSION}-${node_os}-${node_arch}.tar.gz"
-  release_url="${NODE_DIST_BASE}/${NODE_BOOTSTRAP_VERSION}"
-
-  work_dir="$(mktemp -d "${TMPDIR:-/tmp}/mosaic-node-XXXXXX")"
-
-  info "Installing Node.js $NODE_BOOTSTRAP_VERSION ($node_os-$node_arch) to $NODE_ROOT…"
-
-  if ! curl -fsSL "${release_url}/${tarball}" -o "$work_dir/$tarball"; then
-    fail "Download failed: ${release_url}/${tarball}"
-    rm -rf "$work_dir"; return 1
-  fi
-
-  # Trust assumption, stated so nobody has to infer it: this verifies INTEGRITY
-  # (the tarball matches the manifest), not AUTHENTICITY (the manifest is
-  # genuinely Node's). The only thing establishing that is TLS to
-  # $NODE_DIST_BASE. Node publishes SHASUMS256.txt.sig signed by its release
-  # keys and we do not check it, which is on par with nvm but means pointing
-  # MOSAIC_NODE_DIST_BASE at an untrusted mirror has no signature backstop.
-  # Tracked as a hardening follow-up (raised by scooby in the #1229 review).
-  if ! curl -fsSL "${release_url}/SHASUMS256.txt" -o "$work_dir/SHASUMS256.txt"; then
-    fail "Could not fetch SHASUMS256.txt; refusing to install an unverified runtime."
-    rm -rf "$work_dir"; return 1
-  fi
-
-  # Keep only our artifact's line, so a missing entry is an error not a pass.
-  if ! grep " ${tarball}\$" "$work_dir/SHASUMS256.txt" >"$work_dir/expected.sha256"; then
-    fail "$tarball has no entry in SHASUMS256.txt; refusing to install."
-    rm -rf "$work_dir"; return 1
-  fi
-
-  if ! (cd "$work_dir" && verify_sha256 expected.sha256); then
-    fail "Checksum mismatch for $tarball; refusing to install."
-    rm -rf "$work_dir"; return 1
-  fi
-  ok "Checksum verified"
-
-  tar xzf "$work_dir/$tarball" -C "$work_dir"
-  extracted="$work_dir/node-${NODE_BOOTSTRAP_VERSION}-${node_os}-${node_arch}"
-  if [[ ! -x "$extracted/bin/node" ]]; then
-    fail "Extracted archive has no bin/node"
-    rm -rf "$work_dir"; return 1
-  fi
-
-  mkdir -p "$NODE_ROOT"
-  target="$NODE_ROOT/$NODE_BOOTSTRAP_VERSION"
-  rm -rf "$target.incoming"
-  mv "$extracted" "$target.incoming"
-  rm -rf "$target"
-  mv "$target.incoming" "$target"
-  ln -sfn "$NODE_BOOTSTRAP_VERSION" "$NODE_ROOT/current"
-  rm -rf "$work_dir"
-
-  node_bin="$NODE_ROOT/current/bin"
-  if ! node_is_suitable "$node_bin/node"; then
-    fail "Installed node at $node_bin/node did not run"
-    return 1
-  fi
-
-  export PATH="$node_bin:$PATH"
-  ok "Node.js $(node -v) installed with npm $(npm -v 2>/dev/null || echo '?')"
-  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
-  fi
-
-  # 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:$PATH"
-    persist_node_on_path
-    return 0
-  fi
-
-  if [[ "${MOSAIC_SKIP_NODE_BOOTSTRAP:-0}" == "1" ]]; then
-    fail "No suitable Node.js and MOSAIC_SKIP_NODE_BOOTSTRAP=1; refusing to download."
-    echo "  Install Node.js >= $NODE_MIN_MAJOR yourself, then re-run this script."
-    exit 1
-  fi
-
-  require_cmd curl
-  require_cmd tar
-
-  # sha256sum on Linux, shasum on macOS. Verification is not optional: without a
-  # checksum this would install an unauthenticated runtime.
-  if command -v sha256sum &>/dev/null; then
-    verify_sha256() { sha256sum -c --status "$1"; }
-  elif command -v shasum &>/dev/null; then
-    verify_sha256() { shasum -a 256 -c --status "$1"; }
-  else
-    fail "sha256sum or shasum required to verify the Node.js download"
-    exit 1
-  fi
-
-  if ! install_node; then
-    fail "Could not bootstrap Node.js. Install Node.js >= $NODE_MIN_MAJOR and re-run."
-    exit 1
-  fi
-  persist_node_on_path
-}
-
 # ─── preflight ────────────────────────────────────────────────────────────────
 
-ensure_node
 require_cmd node
 require_cmd npm
 
@@ -930,7 +682,11 @@ if [[ "$FLAG_CLI" == "true" ]]; then
     ensure_monorepo
     install_cli_from_source
 
-    ensure_prefix_on_path
+    # PATH check for npm prefix
+    if [[ ":$PATH:" != *":$PREFIX/bin:"* ]]; then
+      warn "$PREFIX/bin is not on your PATH"
+      dim "  Add to your shell rc:  export PATH=\"$PREFIX/bin:\$PATH\""
+    fi
   elif is_next_registry_lane; then
     info "Next mode — trying fast npm @next install from ${REGISTRY}…"
     if install_next_cli_from_registry; then
@@ -943,7 +699,11 @@ if [[ "$FLAG_CLI" == "true" ]]; then
       export MOSAIC_GATEWAY_SKIP_NPM_INSTALL=1
     fi
 
-    ensure_prefix_on_path
+    # PATH check for npm prefix
+    if [[ ":$PATH:" != *":$PREFIX/bin:"* ]]; then
+      warn "$PREFIX/bin is not on your PATH"
+      dim "  Add to your shell rc:  export PATH=\"$PREFIX/bin:\$PATH\""
+    fi
   else
     if [[ -z "$LATEST" ]]; then
       warn "Could not reach registry at $REGISTRY — skipping npm CLI."
@@ -961,7 +721,11 @@ if [[ "$FLAG_CLI" == "true" ]]; then
       ok "CLI is at or ahead of registry ($CURRENT ≥ $LATEST)."
     fi
 
-    ensure_prefix_on_path
+    # PATH check for npm prefix
+    if [[ ":$PATH:" != *":$PREFIX/bin:"* ]]; then
+      warn "$PREFIX/bin is not on your PATH"
+      dim "  Add to your shell rc:  export PATH=\"$PREFIX/bin:\$PATH\""
+    fi
   fi
 fi