Commands: an unknown command id is answered with the nearest command id

A misspelled parameter key got a did-you-mean suggestion, but a
misspelled command id only got "unknown command `select.al`", through
the CLI, MCP and the control channel alike. Session::execute now names
the nearest command id, using the same matching as parameter keys
(ignoring case), and action.batch does the same for an unknown step. An
id with no near match keeps the plain error.

The matching skips candidates whose length differs by more than the
allowed number of edits, so a very long unknown command id or parameter
key is answered at once instead of being measured against every command
id or accepted key.

The new message has a row in every catalog, and docs/mcp.md's
Parameter keys section shows it.

crates/engine/src/cmd/fileio/action_batch.rs

@@ -56,7 +56,13 @@ pub(super) fn action_batch(s: &mut Session, p: &Value) -> Result<Value> {
             return Err(bad(C, "batches cannot nest"));
         }
         if find_command(id).is_none() {
-            return Err(bad(C, format!("commands[{i}]: unknown command `{id}`")));
+            return Err(bad(
+                C,
+                match super::super::params::nearest_command(id) {
+                    Some(near) => format!("commands[{i}]: unknown command `{id}`; did you mean `{near}`?"),
+                    None => format!("commands[{i}]: unknown command `{id}`"),
+                },
+            ));
         }
     }
     let source = str_param(p, "source").unwrap_or("folder");

crates/engine/src/cmd/params.rs

@@ -20,7 +20,7 @@
 
 use serde_json::Value;
 
-use super::{bad, find_command};
+use super::{bad, command_specs, find_command};
 use crate::Result;
 
 /// What a params description says about the keys of the params object.
@@ -208,8 +208,12 @@ fn distance(a: &str, b: &str) -> usize {
 
 /// The key of `keys` a misspelt `key` most likely meant: the nearest one, when it is near.
 fn nearest<'a>(key: &str, keys: &[&'a str]) -> Option<&'a str> {
-    let near = keys.iter().map(|k| (distance(key, k), *k)).min()?;
-    (near.0 <= (key.chars().count() / 3).max(1)).then_some(near.1)
+    let len = key.chars().count();
+    let most = (len / 3).max(1);
+    // A key whose length differs by more than `most` is more than `most` edits away and isn't
+    // measured.
+    let near = keys.iter().filter(|k| k.chars().count().abs_diff(len) <= most).map(|k| (distance(key, k), *k)).min()?;
+    (near.0 <= most).then_some(near.1)
 }
 
 /// `params` has only keys the description `doc` of command `id` names, or the parameter error
@@ -480,6 +484,21 @@ pub fn check_params(id: &str, params: &Value) -> Result<()> {
     Ok(())
 }
 
+/// The command id a misspelled `id`, which names no command, most likely meant: the nearest one,
+/// when it is near (as [`check_keys`] matches a misspelled key).
+pub(crate) fn nearest_command(id: &str) -> Option<&'static str> {
+    let ids: Vec<&'static str> = command_specs().iter().map(|c| c.id).collect();
+    nearest(id, &ids)
+}
+
+/// The error for `id`, which names no command: with the nearest command id, when one is near.
+pub(crate) fn unknown_command(id: &str) -> crate::EngineError {
+    match nearest_command(id) {
+        Some(near) => crate::EngineError::UnknownCommandNear(id.to_string(), near.to_string()),
+        None => crate::EngineError::UnknownCommand(id.to_string()),
+    }
+}
+
 impl crate::Session {
     /// [`check_params`], and [`check_effect_params`] for the effects `effect.setParams` edits in
     /// this session's document (not as a step of a `command.batch`: what it edits is only there

crates/engine/src/lib.rs

@@ -45,6 +45,9 @@ pub use vectorcraft_tools as tools;
 pub enum EngineError {
     #[error("unknown command `{0}`")]
     UnknownCommand(String),
+    /// An unknown command id, with the command id it most likely misspells.
+    #[error("unknown command `{0}`; did you mean `{1}`?")]
+    UnknownCommandNear(String, String),
     #[error("command `{0}` is not available right now: {1}")]
     Disabled(String, String),
     #[error("invalid parameters for `{cmd}`: {msg}")]
@@ -1785,7 +1788,7 @@ impl Session {
 
     /// Execute a command by id. This is THE entry point for every frontend.
     pub fn execute(&mut self, id: &str, params: &Value) -> Result<Value> {
-        let spec = find_command(id).ok_or_else(|| EngineError::UnknownCommand(id.to_string()))?;
+        let spec = find_command(id).ok_or_else(|| cmd::params::unknown_command(id))?;
         // The crate's own tests are the audit of the params descriptions (#1442): a key a test
         // passes that its command's description doesn't name fails the test.
         #[cfg(test)]

crates/engine/src/tests.rs

@@ -90,6 +90,42 @@ fn unknown_and_disabled() {
     assert!(matches!(s.execute("object.group", &json!({})), Err(EngineError::Disabled(..))));
 }
 
+#[test]
+fn unknown_command_names_the_nearest_id() {
+    let mut s = session();
+    for typo in ["select.al", "Select.All", "selcet.all"] {
+        let e = s.execute(typo, &json!({})).unwrap_err();
+        assert!(matches!(&e, EngineError::UnknownCommandNear(id, near) if id == typo && near == "select.all"), "{typo}: {e:?}");
+        assert_eq!(e.to_string(), format!("unknown command `{typo}`; did you mean `select.all`?"));
+    }
+    let e = s.execute("nope", &json!({})).unwrap_err();
+    assert!(matches!(&e, EngineError::UnknownCommand(id) if id == "nope"), "{e:?}");
+    assert_eq!(e.to_string(), "unknown command `nope`");
+    let e = s.execute("command.batch", &json!({"commands": [{"command": "select.al", "params": {}}]})).unwrap_err();
+    assert!(e.to_string().contains("did you mean `select.all`?"), "{e}");
+}
+
+#[test]
+fn a_long_unknown_command_id_is_answered_at_once() {
+    let mut s = session();
+    let long = "x".repeat(200_000);
+    let start = std::time::Instant::now();
+    assert!(matches!(s.execute(&long, &json!({})), Err(EngineError::UnknownCommand(_))));
+    let e = crate::check_params("file.new", &json!({ long.as_str(): 1 })).unwrap_err();
+    assert!(e.to_string().contains("the command takes:"), "{e}");
+    assert!(start.elapsed() < std::time::Duration::from_secs(2), "{:?}", start.elapsed());
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[test]
+fn action_batch_names_the_nearest_command_id() {
+    let mut s = session();
+    let e = s.execute("action.batch", &json!({"source": "dataSets", "commands": [{"command": "select.al"}]})).unwrap_err();
+    assert_eq!(e.to_string(), "invalid parameters for `action.batch`: commands[0]: unknown command `select.al`; did you mean `select.all`?");
+    let e = s.execute("action.batch", &json!({"source": "dataSets", "commands": [{"command": "nope"}]})).unwrap_err();
+    assert_eq!(e.to_string(), "invalid parameters for `action.batch`: commands[0]: unknown command `nope`");
+}
+
 #[test]
 fn group_ungroup() {
     let mut s = session();

crates/ui-egui/src/i18n/bg.tsv

@@ -4224,6 +4224,7 @@ axis	Both	И двете
 @msg	tool shortcuts must be a single key (optionally with Shift)	клавишните комбинации за инструменти трябва да са един клавиш (по избор със Shift)
 @msg	truncated	съкратено
 @msg	unknown command `{0}`	непозната команда `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	непозната команда `{0}`; имахте ли предвид `{1}`?
 @msg	unknown effect `{id}`	непознат ефект `{id}`
 @msg	unknown format	непознат формат
 @msg	unknown format `{f}` (Save writes {_1})	непознат формат `{f}` (Запазването записва {_1})

crates/ui-egui/src/i18n/cs.tsv

@@ -4629,6 +4629,7 @@ imageTrace	Outline	Obrys
 @msg	tool shortcuts must be a single key (optionally with Shift)	zkratky nástrojů musí být jediná klávesa (volitelně se Shift)
 @msg	truncated	zkráceno
 @msg	unknown command `{0}`	neznámý příkaz `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	neznámý příkaz `{0}`; mysleli jste `{1}`?
 @msg	unknown effect `{id}`	neznámý efekt `{id}`
 @msg	unknown format	neznámý formát
 @msg	unknown format `{f}` (Save writes {_1})	neznámý formát `{f}` (Uložit zapisuje {_1})

crates/ui-egui/src/i18n/da.tsv

@@ -4324,6 +4324,7 @@ imageTrace	Outline	Kontur
 @msg	tool shortcuts must be a single key (optionally with Shift)	værktøjsgenveje skal være en enkelt tast (eventuelt med Skift)
 @msg	truncated	afkortet
 @msg	unknown command `{0}`	ukendt kommando `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	ukendt kommando `{0}`; mente du `{1}`?
 @msg	unknown effect `{id}`	ukendt effekt `{id}`
 @msg	unknown format	ukendt format
 @msg	unknown format `{f}` (Save writes {_1})	ukendt format `{f}` (Gem skriver {_1})

crates/ui-egui/src/i18n/de.tsv

@@ -4252,6 +4252,7 @@ theme	Appearance	Erscheinungsbild
 @msg	tool shortcuts must be a single key (optionally with Shift)	Tastaturbefehle für Werkzeuge müssen aus einer einzelnen Taste bestehen (optional mit Shift)
 @msg	truncated	abgeschnitten
 @msg	unknown command `{0}`	unbekannter Befehl `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	unbekannter Befehl `{0}`; meinten Sie `{1}`?
 @msg	unknown effect `{id}`	unbekannter Effekt `{id}`
 @msg	unknown format	unbekanntes Format
 @msg	unknown format `{f}` (Save writes {_1})	unbekanntes Format `{f}` („Speichern“ schreibt {_1})

crates/ui-egui/src/i18n/el.tsv

@@ -4300,6 +4300,7 @@ theme	Appearance	Εμφάνιση
 @msg	tool shortcuts must be a single key (optionally with Shift)	οι συντομεύσεις εργαλείων πρέπει να περιλαμβάνουν ένα πλήκτρο (προαιρετικά με Shift)
 @msg	truncated	περικομμένο
 @msg	unknown command `{0}`	άγνωστη εντολή `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	άγνωστη εντολή `{0}`· μήπως εννοείτε `{1}`;
 @msg	unknown effect `{id}`	άγνωστο εφέ `{id}`
 @msg	unknown format	άγνωστη μορφή
 @msg	unknown format `{f}` (Save writes {_1})	άγνωστη μορφή `{f}` (η Αποθήκευση υποστηρίζει {_1})

crates/ui-egui/src/i18n/es.tsv

@@ -4327,6 +4327,7 @@ axis	Both	Ambos
 @msg	tool shortcuts must be a single key (optionally with Shift)	los atajos de herramientas deben ser una sola tecla (opcionalmente con Shift)
 @msg	truncated	truncado
 @msg	unknown command `{0}`	comando desconocido `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	comando desconocido `{0}`; ¿quiso decir `{1}`?
 @msg	unknown effect `{id}`	efecto desconocido `{id}`
 @msg	unknown format	formato desconocido
 @msg	unknown format `{f}` (Save writes {_1})	formato desconocido `{f}` (Guardar escribe {_1})

crates/ui-egui/src/i18n/fi.tsv

@@ -4536,6 +4536,7 @@ imageTrace	Outline	Ääriviiva
 @msg	tool shortcuts must be a single key (optionally with Shift)	työkalujen pikanäppäinten on oltava yksittäinen näppäin (valinnaisesti Vaihto-näppäimen kanssa)
 @msg	truncated	katkaistu
 @msg	unknown command `{0}`	tuntematon komento `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	tuntematon komento `{0}`; tarkoititko `{1}`?
 @msg	unknown effect `{id}`	tuntematon tehoste `{id}`
 @msg	unknown format	tuntematon muoto
 @msg	unknown format `{f}` (Save writes {_1})	tuntematon muoto `{f}` (Tallenna kirjoittaa muotoja {_1})

crates/ui-egui/src/i18n/fr.tsv

@@ -4324,6 +4324,7 @@ axis	Both	Les deux
 @msg	tool shortcuts must be a single key (optionally with Shift)	les raccourcis d’outils doivent être une seule touche (éventuellement avec Maj)
 @msg	truncated	tronqué
 @msg	unknown command `{0}`	commande inconnue `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	commande inconnue `{0}` ; vouliez-vous dire `{1}` ?
 @msg	unknown effect `{id}`	effet inconnu `{id}`
 @msg	unknown format	format inconnu
 @msg	unknown format `{f}` (Save writes {_1})	format inconnu `{f}` (Enregistrer écrit {_1})

crates/ui-egui/src/i18n/hu.tsv

@@ -5075,6 +5075,7 @@ imageTrace	Outline	Körvonal
 @msg	truncated	csonka
 @msg	Unembedded to {_1}	Beágyazás megszüntetve, ide: {_1}
 @msg	unknown command `{0}`	ismeretlen parancs: `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	ismeretlen parancs: `{0}`; erre gondolt: `{1}`?
 @msg	unknown effect `{id}`	ismeretlen effektus: `{id}`
 @msg	unknown format	ismeretlen formátum
 @msg	unknown format `{f}` (Save writes {_1})	ismeretlen formátum: `{f}` (a Mentés ezeket írja: {_1})

crates/ui-egui/src/i18n/id.tsv

@@ -4324,6 +4324,7 @@ imageTrace	Outline	Kontur
 @msg	tool shortcuts must be a single key (optionally with Shift)	pintasan alat harus satu tombol (opsional dengan Shift)
 @msg	truncated	terpotong
 @msg	unknown command `{0}`	perintah `{0}` tidak dikenal
+@msg	unknown command `{0}`; did you mean `{1}`?	perintah `{0}` tidak dikenal; apakah maksud Anda `{1}`?
 @msg	unknown effect `{id}`	efek `{id}` tidak dikenal
 @msg	unknown format	format tidak dikenal
 @msg	unknown format `{f}` (Save writes {_1})	format `{f}` tidak dikenal (Simpan menulis {_1})

crates/ui-egui/src/i18n/it.tsv

@@ -4367,6 +4367,7 @@ axis	Both	Entrambi
 @msg	tool shortcuts must be a single key (optionally with Shift)	le scelte rapide degli strumenti devono essere un singolo tasto (eventualmente con Shift)
 @msg	truncated	troncato
 @msg	unknown command `{0}`	comando sconosciuto `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	comando sconosciuto `{0}`; forse intendevate `{1}`?
 @msg	unknown effect `{id}`	effetto sconosciuto `{id}`
 @msg	unknown format	formato sconosciuto
 @msg	unknown format `{f}` (Save writes {_1})	formato sconosciuto `{f}` (Salva scrive {_1})

crates/ui-egui/src/i18n/ja.tsv

@@ -4190,6 +4190,7 @@ swatch	Bright Violet	ビビッドバイオレット
 @msg	objects can't be nested more than 32 deep	オブジェクトは 32 階層より深く入れ子にできません
 @msg	the SVG's elements are nested more than {0} deep	SVG の要素が {0} 階層より深く入れ子になっています
 @msg	unknown command `{0}`	`{0}` は不明なコマンドです
+@msg	unknown command `{0}`; did you mean `{1}`?	`{0}` は不明なコマンドです。`{1}` のことですか?
 @msg	`{what}` closes nothing	`{what}` に対応する開始部分がありません
 @msg	`{what}` closes something it didn't open	`{what}` が対応しない開始部分を閉じています
 @msg	a path has too many points	ポイントが多すぎるパスがあります

crates/ui-egui/src/i18n/ka.tsv

@@ -4089,6 +4089,7 @@ font-technology	Variable	ცვლადი
 @msg	tool shortcuts must be a single key (optionally with Shift)	ხელსაწყოს მალსახმობი ერთი კლავიში უნდა იყოს (სურვილისამებრ Shift-ით)
 @msg	truncated	შეკვეცილია
 @msg	unknown command `{0}`	უცნობი ბრძანება `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	უცნობი ბრძანება `{0}`; იქნებ `{1}` იგულისხმეთ?
 @msg	unknown effect `{id}`	უცნობი ეფექტი `{id}`
 @msg	unknown format	უცნობი ფორმატი
 @msg	unknown format `{f}` (Save writes {_1})	უცნობი ფორმატი `{f}` (შენახვა წერს: {_1})

crates/ui-egui/src/i18n/ko.tsv

@@ -4122,6 +4122,7 @@ theme	Appearance	외관
 @msg	objects can't be nested more than 32 deep	개체는 32단계보다 깊게 중첩할 수 없습니다
 @msg	the SVG's elements are nested more than {0} deep	SVG 요소가 {0}단계보다 깊게 중첩되어 있습니다
 @msg	unknown command `{0}`	알 수 없는 명령 `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	알 수 없는 명령 `{0}`: `{1}`을(를) 의미하셨습니까?
 @msg	`{what}` closes nothing	`{what}`이(가) 닫는 항목이 없습니다
 @msg	`{what}` closes something it didn't open	`{what}`이(가) 열지 않은 항목을 닫습니다
 @msg	a path has too many points	패스의 점이 너무 많습니다

crates/ui-egui/src/i18n/nl.tsv

@@ -4336,6 +4336,7 @@ imageTrace	Outline	Contour
 @msg	tool shortcuts must be a single key (optionally with Shift)	gereedschapsneltoetsen moeten uit één toets bestaan (eventueel met Shift)
 @msg	truncated	afgekapt
 @msg	unknown command `{0}`	onbekende opdracht `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	onbekende opdracht `{0}`; bedoelde je `{1}`?
 @msg	unknown effect `{id}`	onbekend effect `{id}`
 @msg	unknown format	onbekende indeling
 @msg	unknown format `{f}` (Save writes {_1})	onbekende indeling `{f}` (Opslaan schrijft {_1})

crates/ui-egui/src/i18n/pl.tsv

@@ -4454,6 +4454,7 @@ imageTrace	Outline	Kontur
 @msg	tool shortcuts must be a single key (optionally with Shift)	skróty narzędzi muszą być pojedynczym klawiszem (opcjonalnie z Shift)
 @msg	truncated	obcięty
 @msg	unknown command `{0}`	nieznane polecenie `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	nieznane polecenie `{0}`; czy chodziło o `{1}`?
 @msg	unknown effect `{id}`	nieznany efekt `{id}`
 @msg	unknown format	nieznany format
 @msg	unknown format `{f}` (Save writes {_1})	nieznany format `{f}` (zapis tworzy {_1})

crates/ui-egui/src/i18n/pt-br.tsv

@@ -3900,6 +3900,7 @@ axis	Both	Ambos
 @msg	tool shortcuts must be a single key (optionally with Shift)	os atalhos de ferramenta devem ser uma única tecla (opcionalmente com Shift)
 @msg	truncated	truncado
 @msg	unknown command `{0}`	comando desconhecido `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	comando desconhecido `{0}`; você quis dizer `{1}`?
 @msg	unknown effect `{id}`	efeito desconhecido `{id}`
 @msg	unknown format	formato desconhecido
 @msg	unknown format `{f}` (Save writes {_1})	formato desconhecido `{f}` (Salvar grava {_1})

crates/ui-egui/src/i18n/ru.tsv

@@ -4363,6 +4363,7 @@ axis	Both	Оба
 @msg	tool shortcuts must be a single key (optionally with Shift)	сочетания инструментов должны быть одной клавишей (необязательно с Shift)
 @msg	truncated	усечено
 @msg	unknown command `{0}`	неизвестная команда `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	неизвестная команда `{0}`; возможно, имелась в виду `{1}`?
 @msg	unknown effect `{id}`	неизвестный эффект `{id}`
 @msg	unknown format	неизвестный формат
 @msg	unknown format `{f}` (Save writes {_1})	неизвестный формат `{f}` (сохранение записывает {_1})

crates/ui-egui/src/i18n/sv.tsv

@@ -4236,6 +4236,7 @@ axis	Both	Båda
 @msg	tool shortcuts must be a single key (optionally with Shift)	kortkommandon för verktyg måste vara en enda tangent (eventuellt med Shift)
 @msg	truncated	avkortad
 @msg	unknown command `{0}`	okänt kommando `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	okänt kommando `{0}`; menade du `{1}`?
 @msg	unknown effect `{id}`	okänd effekt `{id}`
 @msg	unknown format	okänt format
 @msg	unknown format `{f}` (Save writes {_1})	okänt format `{f}` (Spara skriver {_1})

crates/ui-egui/src/i18n/tr.tsv

@@ -4088,6 +4088,7 @@ axis	Both	Her İkisi
 @msg	tool shortcuts must be a single key (optionally with Shift)	araç kısayolları tek tuş olmalıdır (isteğe bağlı olarak Shift ile)
 @msg	truncated	kesik
 @msg	unknown command `{0}`	bilinmeyen komut `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	bilinmeyen komut `{0}`; `{1}` mi demek istediniz?
 @msg	unknown effect `{id}`	bilinmeyen etki `{id}`
 @msg	unknown format	bilinmeyen format
 @msg	unknown format `{f}` (Save writes {_1})	bilinmeyen format `{f}` (Kaydet, {_1} yazar)

crates/ui-egui/src/i18n/uk.tsv

@@ -4351,6 +4351,7 @@ axis	Both	Обидві
 @msg	tool shortcuts must be a single key (optionally with Shift)	поєднання інструментів має бути однією клавішею (необов’язково з Shift)
 @msg	truncated	усічено
 @msg	unknown command `{0}`	невідома команда `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	невідома команда `{0}`; можливо, ви мали на увазі `{1}`?
 @msg	unknown effect `{id}`	невідомий ефект `{id}`
 @msg	unknown format	невідомий формат
 @msg	unknown format `{f}` (Save writes {_1})	невідомий формат `{f}` (збереження записує {_1})

crates/ui-egui/src/i18n/vi.tsv

@@ -4730,6 +4730,7 @@ theme	Appearance	Giao diện
 @msg	truncated	bị cắt ngắn
 @msg	Unembedded to {_1}	Đã bỏ nhúng vào {_1}
 @msg	unknown command `{0}`	lệnh không xác định `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	lệnh không xác định `{0}`; ý bạn là `{1}`?
 @msg	unknown effect `{id}`	hiệu ứng không xác định `{id}`
 @msg	unknown format	định dạng không xác định
 @msg	unknown format `{f}` (Save writes {_1})	định dạng không xác định `{f}` (Lưu ghi {_1})

crates/ui-egui/src/i18n/zh-hans.tsv

@@ -3921,6 +3921,7 @@ imageTrace	Outline	轮廓
 @msg	objects can't be nested more than 32 deep	对象的嵌套不能超过 32 层
 @msg	the SVG's elements are nested more than {0} deep	SVG 的元素嵌套超过 {0} 层
 @msg	unknown command `{0}`	未知命令 `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	未知命令 `{0}`；您是否想输入 `{1}`？
 @msg	`{what}` closes nothing	`{what}` 没有可结束的内容
 @msg	`{what}` closes something it didn't open	`{what}` 结束了并非由它开始的内容
 @msg	a path has too many points	某条路径的点过多

crates/ui-egui/src/i18n/zh-hant.tsv

@@ -1901,6 +1901,7 @@ file-filter	Templates	範本
 @msg	objects can't be nested more than 32 deep	物件的巢狀層級不能超過 32 層
 @msg	the SVG's elements are nested more than {0} deep	SVG 的元素巢狀超過 {0} 層
 @msg	unknown command `{0}`	未知的指令 `{0}`
+@msg	unknown command `{0}`; did you mean `{1}`?	未知的指令 `{0}`；您是指 `{1}` 嗎？
 @msg	`{what}` closes nothing	`{what}` 沒有可結束的內容
 @msg	`{what}` closes something it didn't open	`{what}` 結束了並非由它開始的內容
 @msg	a path has too many points	有一條路徑的點過多

docs/mcp.md

@@ -1030,6 +1030,14 @@ of the format they write (one object can carry several formats' options). A comm
 (`document.setup`, `text.areaOptions`) says so the same way. The app's own journal isn't checked: an action or
 journal recorded by an older version replays as it did, except for an effect `color` that the effect can't read.
 
+An unknown command id is matched the same way as an unknown parameter key: the error names the nearest command id when
+one is near, ignoring case. A step of `command.batch` or `action.batch` gets the same suggestion in its step error:
+
+```json
+{"id": "select.al"}
+→ unknown command `select.al`; did you mean `select.all`?
+```
+
 These Object menu commands refuse a string or another value that is not a number with
 `` `scaleH` must be a number, not "50" ``, naming the key, and change nothing: `scaleH`, `scaleV`, `moveH`, `moveV`
 and `rotate` in `object.transformEach`; `ppi` in `object.rasterize`; `width`, `height`, `spacingX` and `spacingY` in