Now I have everything I need. Here is the ADR:

Shipwright exposes 100+ subcommands through a central CLI router (scripts/sw). Each command is a standalone bash script (scripts/sw-<name>.sh) dispatched via a case statement using exec. A hello command already exists as the canonical reference implementation of this pattern.

The ping command is a minimal health-check primitive: shipwright ping → prints pong to stdout, exits 0. It has no external dependencies, no side effects, and no state. The only constraints are:

1. Must conform to the established Standalone Script Pattern (identical structure to sw-hello.sh)
2. Must be Bash 3.2 compatible (no associative arrays, no ${var,,}, no readarray)
3. Must use set -euo pipefail + ERR trap
4. Must carry VERSION="3.2.4" to stay consistent with the rest of the codebase
5. Output must be exactly pong — no color prefix, no ANSI escape codes — because tests do an exact-string comparison

Standalone Script Pattern — create scripts/sw-ping.sh as a structural clone of scripts/sw-hello.sh with a single behavioral change: the no-argument case prints echo "pong" instead of echo "hello world".

The router entry (ping) case in scripts/sw) is inserted before hello) at line 605. The *)catch-all at line 608 is the unreachable-command guard; any new entry must be placed before it.

The test file (scripts/sw-ping-test.sh) is a structural clone of scripts/sw-hello-test.sh — inline assert_equals/assert_exit_code helpers, 6 test functions, PASS/FAIL counters, exits 1 on any failure.

Note on package.json insertion point: The plan states insertion between sw-pipeline-vitals-test.sh and sw-pm-test.sh. This is incorrect. Alphabetically, ping (p-i-n) sorts before pipeline (p-i-p) because n < p. The correct insertion is between sw-patrol-meta-test.sh and sw-pipeline-composer-test.sh.

1. Inline the ping handler in the router (scripts/sw) — Pros: zero new files, no exec overhead. Cons: violates Single Responsibility — the router is a dispatcher, not an implementer; breaks the test boundary (no independent bash scripts/sw-ping-test.sh path); against established architecture for all 100+ commands. Rejected.

2. Add ping as a shared library function — Pros: reusable if multiple scripts need a health check. Cons: premature abstraction for a one-line output; introduces a dependency where none exists; over-engineered for the requirement. Rejected.

None. No new packages, no new shared libraries.

 ┌─────────────────────────────────────┐
 │ scripts/sw │
 │ (CLI Router) │
 │ │
 │ case "$cmd" in │
 │ ping) exec sw-ping.sh "$@" ;; │◄── NEW (line 605, before hello)
 │ hello) exec sw-hello.sh "$@" ;; │
 │ *) error "Unknown cmd" ;; │
 │ esac │
 └──────────────┬──────────────────────┘
 │ exec (replaces process)
 ▼
 ┌─────────────────────────────────────┐
 │ scripts/sw-ping.sh │
 │ (Command Handler) │
 │ │
 │ main() │
 │ case "${1:-}" in │
 │ --help|-h) show_help; exit 0 │
 │ --version) echo $VERSION; │
 │ exit 0 │
 │ "") echo "pong"; │◄── CORE BEHAVIOR
 │ exit 0 │
 │ *) error; exit 1 │
 │ esac │
 └─────────────────────────────────────┘
 ▲さんかく
 │ bash invocation
 ┌─────────────────────────────────────┐
 │ scripts/sw-ping-test.sh │
 │ (Test Harness) │
 │ │
 │ assert_equals "pong" "$output" │
 │ assert_exit_code 0 $? │
 │ [[ output =~ "USAGE" ]] │
 │ [[ output =~ semver ]] │
 │ || local exit_code=$? (exit 1) │
 └─────────────────────────────────────┘

# sw-ping.sh — public interface (all args optional)
#
# Input: 1ドル — optional flag: --help | -h | --version | -v | (empty)
# Output: stdout — "pong" (no-arg), help text (--help/-h), semver (--version/-v)
# Stderr: error message on unknown option
# Exit: 0 — success (pong, help, version)
# 1 — unknown option
sw_ping() {
 # "" → echo "pong" to stdout, exit 0
 # --help/-h → echo help text to stdout, exit 0
 # --version → echo "$VERSION" to stdout, exit 0
 # * → echo error to stderr, echo help, exit 1
}
# Router dispatch (scripts/sw)
# Precondition: $cmd == "ping"
# Postcondition: process replaced by sw-ping.sh via exec (no return)
ping) exec "$SCRIPT_DIR/sw-ping.sh" "$@" ;;

User invokes: shipwright ping
 │
 ▼
scripts/sw main()
 → parses 1ドル as $cmd
 → case "ping" → exec sw-ping.sh (stdin/stdout/stderr inherited)
 │
 ▼
sw-ping.sh main()
 → case "${1:-}" — no arg: ""
 → echo "pong" ← single call, no color prefix
 → exit 0
 │
 ▼
stdout: "pong\n"
exit code: 0

For the test path:

bash scripts/sw-ping-test.sh
 → output=$("$SCRIPT_DIR/sw-ping.sh") ← subshell, stdout captured
 → assert_equals "pong" "$output" ← $() strips trailing newline
 → PASS++

• bash scripts/sw-ping.sh prints exactly pong (no color codes, no prefix characters)
• bash scripts/sw-ping.sh exits with code 0
• bash scripts/sw-ping.sh --help contains the string USAGE
• bash scripts/sw-ping.sh -h contains the string USAGE
• bash scripts/sw-ping.sh --version matches ^[0-9]+\.[0-9]+\.[0-9]+
• bash scripts/sw-ping.sh --invalid exits with code 1
• bash scripts/sw-ping-test.sh reports PASS: 6 FAIL: 0
• bash scripts/sw ping prints pong (router integration verified)
• npm test passes with sw-ping-test.sh included and no regressions in existing suites
• sw-ping.sh is executable (ls -l scripts/sw-ping.sh | grep ^-rwx)
• scripts/sw ping) case appears before hello) and before *)