feat(install): add --init flag for ephemeral wizard runs

Adds `--init` to the install script so users can run the setup wizard
without permanently installing the CLI:

    curl -fsSL https://cli.sentry.dev/install | bash -s -- --init

Downloads the binary to a temp path, runs `sentry init`, and cleans up.
Skips download entirely if `sentry` is already in PATH. All args after
`--init` are forwarded to the wizard (--dry-run, --yes, org/project).

Closes #682

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: betegon

install

@@ -83,6 +83,7 @@ Usage: install [options]
 Options:
     -h, --help              Display this help message
     -v, --version <version> Install a specific version (e.g., 0.2.0) or "nightly"
+        --init              Run \`sentry init\` ephemerally without installing the CLI
         --no-modify-path    Don't modify shell config files (.zshrc, .bashrc, etc.)
         --no-completions    Don't install shell completions
 
@@ -94,6 +95,7 @@ Examples:
     curl -fsSL https://cli.sentry.dev/install | bash
     curl -fsSL https://cli.sentry.dev/install | bash -s -- --version nightly
     curl -fsSL https://cli.sentry.dev/install | bash -s -- --version 0.19.0
+    curl -fsSL https://cli.sentry.dev/install | bash -s -- --init
     SENTRY_VERSION=nightly curl -fsSL https://cli.sentry.dev/install | bash
     SENTRY_INSTALL_DIR=~/.local/bin curl -fsSL https://cli.sentry.dev/install | bash
 EOF
@@ -102,6 +104,8 @@ EOF
 requested_version="${SENTRY_VERSION:-}"
 no_modify_path=false
 no_completions=false
+init_mode=false
+init_args=()
 while [[ $# -gt 0 ]]; do
   case "$1" in
     -h|--help) usage; exit 0 ;;
@@ -113,6 +117,13 @@ while [[ $# -gt 0 ]]; do
         die "Error: --version requires a version argument" "args"
       fi
       ;;
+    --init)
+      init_mode=true
+      shift
+      # Remaining args are forwarded to `sentry init`
+      init_args=("$@")
+      break
+      ;;
     --no-modify-path)
       no_modify_path=true
       shift
@@ -125,6 +136,12 @@ while [[ $# -gt 0 ]]; do
   esac
 done
 
+# In init mode, skip download if the CLI is already installed.
+if [[ "$init_mode" == "true" ]] && command -v sentry >/dev/null 2>&1; then
+  echo -e "${MUTED}sentry found in PATH, running init directly...${NC}"
+  exec sentry init ${init_args[@]+"${init_args[@]}"}
+fi
+
 # Detect OS
 case "$(uname -s)" in
   Darwin*) os="darwin" ;;
@@ -253,26 +270,33 @@ fi
 
 chmod +x "$tmp_binary"
 
-# Delegate installation and configuration to the binary itself.
-# setup --install handles: directory selection, binary placement, PATH,
-# completions, agent skills, and the welcome message.
-# --channel persists the release channel so future `sentry cli upgrade`
-# calls track the same channel without requiring a flag.
-if [[ "$requested_version" == "nightly" ]]; then
-  channel="nightly"
+if [[ "$init_mode" == "true" ]]; then
+  # Ephemeral mode: run the wizard and clean up. The EXIT trap (set earlier)
+  # removes the temp binary. The binary inherits the terminal's stdin (the
+  # pipe is already consumed by bash), so interactive prompts work normally.
+  "$tmp_binary" init ${init_args[@]+"${init_args[@]}"}
 else
-  channel="stable"
-fi
-setup_args="--install --method curl --channel $channel"
-if [[ "$no_modify_path" == "true" ]]; then
-  setup_args="$setup_args --no-modify-path"
-fi
-if [[ "$no_completions" == "true" ]]; then
-  setup_args="$setup_args --no-completions"
-fi
+  # Delegate installation and configuration to the binary itself.
+  # setup --install handles: directory selection, binary placement, PATH,
+  # completions, agent skills, and the welcome message.
+  # --channel persists the release channel so future `sentry cli upgrade`
+  # calls track the same channel without requiring a flag.
+  if [[ "$requested_version" == "nightly" ]]; then
+    channel="nightly"
+  else
+    channel="stable"
+  fi
+  setup_args="--install --method curl --channel $channel"
+  if [[ "$no_modify_path" == "true" ]]; then
+    setup_args="$setup_args --no-modify-path"
+  fi
+  if [[ "$no_completions" == "true" ]]; then
+    setup_args="$setup_args --no-completions"
+  fi
 
-# Remove trap — setup will handle temp cleanup on success
-trap - EXIT
+  # Remove trap — setup will handle temp cleanup on success
+  trap - EXIT
 
-# shellcheck disable=SC2086
-"$tmp_binary" cli setup $setup_args
+  # shellcheck disable=SC2086
+  "$tmp_binary" cli setup $setup_args
+fi