fix(cli): make --dry-run refuse what the real run refuses, and answer help

CHANGELOG.md

@@ -43,6 +43,25 @@ Notable changes to Chrono Mock, newest first. The format follows
 
 ### Fixed
 
+- **`--dry-run` approved sessions the real run refuses.** An impossible `--at` (month 13, 30 February,
+  25:61) was printed as the plan and exited 0, while the real run was refused by the core with
+  exit 1. A file Windows will not start (a text file, an empty `.exe`, one cut short inside its
+  header, a library) was planned as "native injection" and exited 0, while the real run failed to
+  launch it with exit 2. The plan now refuses both with the code the real run gives, the moment in
+  the core's own words. It reads the header where the file says it is, so a program whose header
+  sits far into the file is still planned. What it leaves to the real run is whether the rest of the
+  file is intact. A batch script is still planned, because Windows starts it through the command
+  interpreter. `chronomock.plan/1` names that target state `not_a_program`.
+- **A preset that dates from the application's file carried the time of day the file was written.**
+  `chrono run --preset date-before-install` without `--param` set the session to 23:00:35 the day
+  before installation, where the same preset given the date by hand sets midnight. A date parameter
+  is a date, so the file's creation date now arrives as midnight too. The trial presets were not
+  affected, because they set their own time.
+- **Asking for help was answered as a mistake.** `chrono help` said "unknown command", and
+  `chrono calc --help` said "unknown flag" and exited 1, while `chrono --help` exited 0. `help`,
+  `run --help` and `calc --help` (and `-h`) now print the usage and exit 0. `--help` further along the
+  command line is still passed to the application. `--at` followed by another flag, or by `-h`, now
+  says that `--at` is missing its moment, instead of a sentence about a "shift".
 - **Ending a session sent the application's timers back, and left its web pages on the session
   date.** A session often ends while the application keeps running: `--ticks` ran out, or the
   session was stopped from the window. The application was then handed back the real value of every

crates/cli/src/cli.rs

@@ -235,6 +235,28 @@ pub(crate) fn print_usage() {
     eprintln!("usage: chrono license [--components]   (also --license)   the licence, the warranty disclaimer, and every bundled component with its version");
 }
 
+/// Whether a word is the help flag, which every command answers.
+pub(crate) fn is_help_flag(word: &str) -> bool {
+    matches!(word, "--help" | "-h")
+}
+
+/// Whether the words after a command ask for its help: `run --help`, `calc -h`. Only the FIRST word
+/// counts, because `--help` further along can be meant for the target (`--args --help`).
+pub(crate) fn asks_for_help(rest: &[String]) -> bool {
+    rest.first().is_some_and(|word| is_help_flag(word))
+}
+
+/// The usage a command was asked for, and exit 0 - it is an answer, not a refusal. `calc --help`
+/// used to say "unknown flag" and exit 1 while `chrono --help` beside it exited 0.
+pub(crate) fn print_help_for(command: &str) -> i32 {
+    if command == "calc" {
+        print_calc_usage();
+    } else {
+        print_usage();
+    }
+    0
+}
+
 pub(crate) fn print_calc_usage() {
     eprintln!("usage: chrono calc [--base <today|now|YYYY-MM-DDTHH:MM:SS>] [--base-utc <YYYY-MM-DDTHH:MM:SS[Z]>] [--shift <±N<unit>>]... [--set-time <HH:MM:SS>] [--snap <target>] [--nearest <target>] [--to-zone <+HH:MM>] [--zone <+HH:MM>] [--calendar <us-banking|us-federal|pl>] [--format <mask>] [--json]");
     eprintln!("       or: chrono calc --preset <id> [--param id=value]...   (named moment, e.g. month-end, trial-first-day-after)");

crates/cli/src/main.rs

@@ -63,14 +63,15 @@ mod zone;
 
 use calc::calc_run;
 use cdp_probe::{cdp_date_probe, cdp_launch_probe, cdp_probe, cdp_shim_probe};
-use cli::{print_license, print_usage, print_version};
+use cli::{asks_for_help, print_help_for, print_license, print_usage, print_version};
 use core::core_mode;
 use run::driver_run;
 
 fn main() {
     let args: Vec<String> = std::env::args().collect();
     let code = match args.get(1).map(String::as_str) {
         Some("__core") => core_mode(),
+        Some(command @ ("run" | "calc")) if asks_for_help(&args[2..]) => print_help_for(command),
         Some("run") => driver_run(&args[2..]),
         Some("calc") => calc_run(&args[2..]),
         Some("__cdp-probe") => cdp_probe(&args[2..]),
@@ -83,7 +84,7 @@ fn main() {
             0
         }
         Some("license") | Some("--license") => print_license(&args[2..]),
-        Some("--help") | Some("-h") | None => {
+        Some("--help") | Some("-h") | Some("help") | None => {
             print_usage();
             0
         }