feat(install): install without administrator rights (--no-admin)

Codeman itself always lived under $HOME; administrator rights were only
spent on what it needs first (system packages for Node.js, tmux and git,
Homebrew on a Mac). An account without those rights could not install it:
the installer died in ensure_sudo, or in Homebrew's own installer.

install.sh now has a no-admin route, taken by itself when the account has
no administrator rights (no sudo binary; outside sudo/wheel/admin and
`sudo -n true` fails; a refused sudo password; a Mac account outside the
admin group with no writable Homebrew) and forced with --no-admin or
CODEMAN_NO_ADMIN=1:

- Node.js: the official tarball from nodejs.org, checked against the
  SHASUMS256.txt published beside it, into ~/.codeman/runtime/node.
- tmux: the tmux project's own build (tmux/tmux-builds 3.7c), checked
  against a SHA-256 pinned in the installer, into ~/.codeman/runtime/bin.
- Both are linked from ~/.local/bin (never over a file that is not ours),
  and the runtime is on PATH and on the LaunchAgent's PATH.
- git is never installed. Without a working git the source comes as an
  archive, the install is marked with .install-source, and it updates by
  re-running the installer: the new tree is built beside the old one and
  swapped in only after the build succeeded. A later re-run on a machine
  that has gained git turns it back into a clone.
- Nothing on this route runs sudo, Homebrew or `xcode-select --install`,
  and the route is never decided by `sudo -v`.

What it cannot supply is checked before the first download: a C/C++
toolchain on Linux (node-pty 1.1.0 compiles there), musl, and macOS below
15 (the tmux build's deployment target).

Along the way:

- check_git no longer trusts `command -v git`. On a Mac without the Xcode
  Command Line Tools /usr/bin/git is a stub that opens Apple's install
  dialog; it is judged by `xcode-select -p` and never executed. Any other
  git is asked for its version.
- scripts/git-hooks.mjs answers "not a checkout" without running git, for
  the same reason: postinstall calls it on every npm install.
- The in-app updater knows the install kind `archive` and points such an
  install at the installer instead of `npm i -g aicodeman@latest`.
- download() and download_to_stdout() resolve DOWNLOADER themselves. Only
  main() used to set it, so `install.sh cloudflared` died on `set -u` with
  the message swallowed by the step log.
- The AI CLI menu leaves out a Homebrew-only install command where there
  is no Homebrew.

Verified with the real installer: a bare Ubuntu 24.04 container as an
unprivileged user (install, a PTY round trip through the API, update by
re-run, cloudflared, uninstall), the same without a compiler (stops before
any download), with a broken then working git, with sudo present but not
usable, and on macOS 26 (arm64) in an isolated HOME with sudo, brew, git,
the compilers, launchctl and tailscale replaced by tripwires. Not verified
on a real standard macOS account: that account was an administrator.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -151,6 +151,61 @@ jobs:
             RECONFIGURE=0; parse_flags --port 4001; [[ "$RECONFIGURE" == "1" ]]
             echo "bash $BASH_VERSION: question phase (flags, launch default, occupied :443, rename opt-in, kept password, start line) ok"
           '
+          # No-admin route: the helpers that decide what gets downloaded and whether it is
+          # trusted (the Node.js checksum pick, the tmux digest table, the verify step), the
+          # stop-before-download check, and an archive install plus its replacement, all
+          # in bash 3.2. This image is Alpine, so it is also the one place the musl branch
+          # runs for real: a machine the route cannot serve must stop BEFORE a download.
+          docker run --rm -v "$PWD":/w -w /w -e CODEMAN_INSTALL_SH_LIB=1 -e HOME=/tmp/h bash:3.2 bash -c '
+            set -euo pipefail
+            mkdir -p /tmp/h /tmp/src/Codeman-1/src
+            . /w/install.sh
+            sha=$(printf "%064d" 7)
+            sums=$(printf "%s  node-v22.1.0-linux-x64.tar.gz\nnothex  node-v22.1.0-linux-arm64.tar.gz\n" "$sha")
+            [[ "$(printf "%s\n" "$sums" | pick_node_tarball linux-x64)" == "$sha node-v22.1.0-linux-x64.tar.gz" ]]
+            if printf "%s\n" "$sums" | pick_node_tarball linux-arm64 >/dev/null; then
+              echo "accepted a checksum that is not 64 hex digits" >&2; exit 1
+            fi
+            for p in linux-x86_64 linux-arm64 macos-arm64 macos-x86_64; do
+              d=$(tmux_build_sha256 "$p"); [[ ${#d} -eq 64 ]]
+            done
+            printf codeman > /tmp/f; good=$(sha256_file /tmp/f); [[ ${#good} -eq 64 ]]
+            verify_sha256 /tmp/f "$good"
+            if verify_sha256 /tmp/f "${good%?}x" || verify_sha256 /tmp/f ""; then
+              echo "accepted a wrong or empty checksum" >&2; exit 1
+            fi
+            is_musl_libc
+            NO_ADMIN=1; NONINTERACTIVE=1
+            download() { echo DOWNLOADED; }; download_to_stdout() { echo DOWNLOADED; }
+            check_node() { return 1; }; check_tmux() { return 1; }; check_git() { return 1; }
+            check_build_tools() { return 0; }
+            if out=$( (ask_dependencies_no_admin linux) 2>&1 ); then
+              echo "did not stop on a musl system" >&2; exit 1
+            fi
+            case "$out" in
+              *DOWNLOADED*) echo "downloaded before stopping: $out" >&2; exit 1 ;;
+              *musl*) ;;
+              *) echo "stopped for the wrong reason: $out" >&2; exit 1 ;;
+            esac
+            # An archive install, then its replacement beside it (busybox tar, bash 3.2).
+            printf "{ \"version\": \"1.0.0\" }\n" > /tmp/src/Codeman-1/package.json
+            tar -czf /tmp/one.tar.gz -C /tmp/src Codeman-1
+            printf "{ \"version\": \"2.0.0\" }\n" > /tmp/src/Codeman-1/package.json
+            tar -czf /tmp/two.tar.gz -C /tmp/src Codeman-1
+            INSTALL_DIR=/tmp/h/app; LOG_FILE=/dev/null
+            download() { cp "${1#file://}" "$2"; }; run_step() { shift; "$@"; }
+            CODEMAN_TARBALL_URL=file:///tmp/one.tar.gz; install_or_update_repo >/dev/null 2>&1; finish_source_swap
+            [[ -f "$INSTALL_DIR/$SOURCE_MARKER" && -z "$SOURCE_STAGING" ]]
+            grep -q 1.0.0 "$INSTALL_DIR/package.json"
+            touch "$INSTALL_DIR/from-the-old-build"
+            CODEMAN_TARBALL_URL=file:///tmp/two.tar.gz; install_or_update_repo >/dev/null 2>&1
+            [[ "$SOURCE_STAGING" == "$INSTALL_DIR.new" ]] && grep -q 1.0.0 "$INSTALL_DIR/package.json"
+            finish_source_swap
+            grep -q 2.0.0 "$INSTALL_DIR/package.json"
+            [[ ! -e "$INSTALL_DIR/from-the-old-build" && ! -e "$INSTALL_DIR.new" && ! -e "$INSTALL_DIR.old" ]]
+            NO_ADMIN=""; resolve_admin_mode; [[ "$NO_ADMIN" == "0" ]]
+            echo "bash $BASH_VERSION: no-admin route (checksums, stop before download, archive install and swap) ok"
+          '
 
       - name: CLI catalogue artifacts are in sync with stock.ts
         run: npm run generate:cli-catalog -- --check