feat: splitting

src/model/bank.rs

@@ -352,8 +352,10 @@ fn validate_item(
     if it.stem.trim().is_empty() {
         issues.push("empty stem".into());
     }
-    if it.version == 0 {
-        issues.push("version must be at least 1".into());
+    if let Some(replaced) = &it.supersedes {
+        if *replaced == it.id {
+            issues.push("supersedes names this item".into());
+        }
     }
 
     // --- options ----
@@ -379,15 +381,22 @@ fn validate_item(
         if o.text.trim().is_empty() {
             issues.push(format!("option {pos}: empty text"));
         }
-        let letter_ok = o.id.len() == 1
-            && o.id
-                .chars()
-                .next()
-                .map(|c| c.is_ascii_uppercase() && c <= 'H')
-                .unwrap_or(false);
-        if !letter_ok {
+        // Two forms are accepted: the 2.0 name, and the letter that preceded
+        // it. A bank migrates when `coursebank migrate options` is run on it,
+        // not when the tool is upgraded, so a course mid-migration still loads.
+        let slug_ok = o.id.strip_prefix("o-").is_some_and(|rest| {
+            !rest.is_empty()
+                && !rest.starts_with('-')
+                && !rest.ends_with('-')
+                && !rest.contains("--")
+                && rest
+                    .chars()
+                    .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-')
+        });
+        if !slug_ok && !Item::is_legacy_option_id(&o.id) {
             issues.push(format!(
-                "option {pos}: id `{}` must be a single letter A through H",
+                "option {pos}: id `{}` is neither a name such as `o-fourth-line` nor a pre-2.0 \
+                 letter A through H",
                 o.id
             ));
         }
@@ -514,10 +523,10 @@ fn validate_item(
                 ));
             }
         }
-        for letter in c.option_stats.keys() {
-            if it.option(letter).is_none() {
+        for option in c.option_stats.keys() {
+            if it.option(option).is_none() {
                 issues.push(format!(
-                    "calibration.option_stats has `{letter}`, which is not an option of this item"
+                    "calibration.option_stats has `{option}`, which is not an option of this item"
                 ));
             }
         }
@@ -533,25 +542,6 @@ fn validate_item(
         }
     }
 
-    // --- history must be coherent ------
-    let mut last_version = 0u32;
-    for (i, h) in it.history.iter().enumerate() {
-        if h.version <= last_version {
-            issues.push(format!(
-                "history entry {} has version {} which does not increase",
-                i + 1,
-                h.version
-            ));
-        }
-        last_version = h.version;
-    }
-    if !it.history.is_empty() && last_version > it.version {
-        issues.push(format!(
-            "history records version {last_version} but the item says version {}",
-            it.version
-        ));
-    }
-
     // --- retirement -----
     if it.retired.is_some() && it.status != Status::Retired {
         issues.push(format!(
@@ -1027,27 +1017,6 @@ learning_targets:
         );
     }
 
-    #[test]
-    fn history_versions_must_increase() {
-        let b = bank(
-            r#"
-  - id: q-a-001
-    version: 2
-    status: draft
-    level: 1
-    stem: s
-    options:
-      - { id: A, text: a, correct: true }
-      - { id: B, text: b }
-    history:
-      - { version: 2, date: 2026-01-01, change: second }
-      - { version: 1, date: 2026-01-02, change: first }
-"#,
-        );
-        let issues = b.validate(None);
-        assert!(issues.iter().any(|i| i.contains("does not increase")));
-    }
-
     #[test]
     fn level_counts_exclude_drafts_and_bonuses() {
         let b = bank(