feat: improve worksheet

.gitignore

@@ -1,4 +1,5 @@
 preview
+scratch
 
 /dist/
 /THIRD-PARTY-LICENSES.txt

src/analysis/irt.rs

@@ -444,7 +444,7 @@ pub fn fit(matrix: &Matrix, opts: &Options) -> Fit {
     for iteration in 0..opts.max_iterations {
         iterations = iteration + 1;
 
-        // ---- E step: expected counts at each quadrature point ----
+        // --- E step: expected counts at each quadrature point ----
         // Counts are accumulated per item rather than globally, so an item
         // administered to only some examinees is not charged for the others.
         let mut n_kj = vec![vec![0.0f64; j_count]; n_quad];
@@ -473,7 +473,7 @@ pub fn fit(matrix: &Matrix, opts: &Options) -> Fit {
             }
         }
 
-        // ---- M step: one two-parameter Newton solve per item ----
+        // --- M step: one two-parameter Newton solve per item ----
         let mut delta = 0.0f64;
         for j in 0..j_count {
             let counts: Vec<(f64, f64)> = (0..n_quad).map(|k| (n_kj[k][j], r_k[k][j])).collect();
@@ -529,7 +529,7 @@ pub fn fit(matrix: &Matrix, opts: &Options) -> Fit {
         ));
     }
 
-    // ---- Standard errors and per-item notes ----
+    // --- Standard errors and per-item notes ----
     let (grid_final, weight_final) = (grid.clone(), base_weight.clone());
     let mut p_grid = vec![vec![0.0f64; j_count]; n_quad];
     for k in 0..n_quad {
@@ -601,7 +601,7 @@ pub fn fit(matrix: &Matrix, opts: &Options) -> Fit {
         });
     }
 
-    // ---- Abilities, expected a posteriori ----
+    // --- Abilities, expected a posteriori ----
     let mut abilities = Vec::with_capacity(n);
     let mut log_likelihood = 0.0f64;
     for i in 0..n {

src/authoring/jsonschema.rs

@@ -571,6 +571,77 @@ fn asset_schema() -> Value {
     })
 }
 
+/// The worked solution, and for an open-response item how it is graded.
+fn solution_schema() -> Value {
+    json!({
+        "type": "object",
+        "additionalProperties": false,
+        "description": "The answer, the reasoning, and the rubric. Rendered in the solutions \
+                        document and the answer key, never in a question paper.",
+        "properties": {
+            "model_answer": {
+                "type": "string",
+                "description": "For an open-response item, the response a full-credit student \
+                                writes; for a choice item, an optional one-line statement of the key."
+            },
+            "explanation": {
+                "type": "string",
+                "description": "The worked reasoning a student learns from. The body of the \
+                                solutions entry."
+            },
+            "rubric": { "type": "array", "items": rubric_criterion_schema() },
+            "accepted": {
+                "type": "array",
+                "items": { "type": "string" },
+                "description": "Responses a short constructed answer is accepted as."
+            },
+            "review": {
+                "type": "array",
+                "items": citation_schema(),
+                "description": "Where to look again after missing this item."
+            }
+        }
+    })
+}
+
+/// One rubric line for an open-response item.
+fn rubric_criterion_schema() -> Value {
+    json!({
+        "type": "object",
+        "required": ["description"],
+        "additionalProperties": false,
+        "properties": {
+            "description": text("What earns the points on this line."),
+            "points": { "type": "number", "minimum": 0.0 }
+        }
+    })
+}
+
+/// A citation into the reference registry, written as an object or a bare string.
+fn citation_schema() -> Value {
+    json!({
+        "oneOf": [
+            { "type": "string", "description": "A citation, unparsed." },
+            citation_mapping_schema()
+        ]
+    })
+}
+
+/// The object form of a citation.
+fn citation_mapping_schema() -> Value {
+    json!({
+        "type": "object",
+        "additionalProperties": false,
+        "properties": {
+            "ref": text("Citation key into `references`."),
+            "locator": { "type": "string", "description": "Where inside the work: §6.1, pp. 4-9." },
+            "path": { "type": "string", "description": "Joined to the reference base_url." },
+            "url": { "type": "string" },
+            "text": { "type": "string" }
+        }
+    })
+}
+
 /// The schema for authored design intent.
 fn design_schema() -> Value {
     json!({
@@ -738,9 +809,10 @@ fn item_identity_properties() -> Value {
         "cognitive_process": cognitive_process(),
         "format": {
             "type": "string",
-            "enum": ["single_best_answer", "multiple_response", "true_false"],
-            "description": "single_best_answer requires exactly one keyed option; \
-                            multiple_response requires at least two."
+            "enum": ["single_best_answer", "multiple_response", "true_false", "open_response"],
+            "description": "single_best_answer keys exactly one option; multiple_response keys \
+                            two or more; open_response takes no options and is graded from its \
+                            solution."
         },
         "bonus": { "type": "boolean" },
         "points": { "type": "number", "exclusiveMinimum": 0.0 },
@@ -767,8 +839,10 @@ fn item_content_properties() -> Value {
             "type": "array",
             "minItems": 2,
             "maxItems": 8,
+            "description": "Absent for an open_response item; at least two for any choice format.",
             "items": option_schema()
         },
+        "solution": solution_schema(),
         "learning_objectives": string_array(
             "Objective ids this item measures. Reports aggregate on these, so an item with none \
              contributes to nothing."
@@ -807,7 +881,7 @@ fn item_schema() -> Value {
     }
     json!({
         "type": "object",
-        "required": ["id", "level", "stem", "options"],
+        "required": ["id", "level", "stem"],
         "additionalProperties": false,
         "properties": Value::Object(properties)
     })

src/authoring/lint.rs

@@ -421,7 +421,7 @@ pub fn lint_item(entry: &Entry, course: &CourseFile, t: &Thresholds) -> Vec<Find
         });
     };
 
-    // ---------------------------------------------------------------- clarity
+    // --- clarity
     let stem = it.stem.trim();
     let stem_lower = stem.to_lowercase();
     let words: Vec<&str> = stem.split_whitespace().collect();
@@ -513,7 +513,7 @@ pub fn lint_item(entry: &Entry, course: &CourseFile, t: &Thresholds) -> Vec<Find
         );
     }
 
-    // ----------------------------------------------------------------- cueing
+    // --- cueing
     let keys: Vec<&crate::item::Choice> = it.options.iter().filter(|o| o.correct).collect();
     let distractors: Vec<&crate::item::Choice> = it.options.iter().filter(|o| !o.correct).collect();
 
@@ -659,7 +659,7 @@ pub fn lint_item(entry: &Entry, course: &CourseFile, t: &Thresholds) -> Vec<Find
         }
     }
 
-    // ----------------------------------------------------------- completeness
+    // --- completeness
     // These are only worth insisting on once an item is meant to be used.
     let is_ready = matches!(it.status, Status::Approved | Status::InReview);
     if is_ready {
@@ -749,7 +749,7 @@ pub fn lint_item(entry: &Entry, course: &CourseFile, t: &Thresholds) -> Vec<Find
         }
     }
 
-    // --------------------------------------------------------------- evidence
+    // --- evidence
     if !it.calibration_is_current() {
         push(
             Rule::StaleCalibration,
@@ -868,6 +868,12 @@ fn lint_option_counts(catalog: &Catalog) -> Vec<Finding> {
         if e.item.status == Status::Retired {
             continue;
         }
+        // An open-response item carries no options, so it is neither part of the
+        // count norm nor able to deviate from it. Leaving it out keeps a bank of
+        // four-option questions from reporting every essay as an odd count.
+        if !e.item.has_options() {
+            continue;
+        }
         by_bank.entry(e.bank.as_str()).or_default().push(e);
     }
 

src/authoring/select.rs

@@ -84,7 +84,7 @@ pub fn select(
     let seed = blueprint.seed.unwrap_or(0);
     let mut notes = Vec::new();
 
-    // ------------------------------------------------------------------ pool
+    // --- pool
     let eligible: Vec<&crate::catalog::Entry> = catalog
         .assemblable()
         .into_iter()
@@ -101,7 +101,7 @@ pub fn select(
     let mut chosen: Vec<String> = Vec::new();
     let mut per_bank: BTreeMap<String, usize> = BTreeMap::new();
 
-    // ---------------------------------------------------- objective minimums
+    // --- objective minimums
     // Placed first, because a coverage requirement is the constraint most likely
     // to become unsatisfiable once the level quotas are full.
     for (objective, needed) in &blueprint.objective_minimums {
@@ -140,7 +140,7 @@ pub fn select(
         }
     }
 
-    // ------------------------------------------------------- level quotas
+    // --- level quotas
     let mut scored: Vec<String> = Vec::new();
     for (level, want) in &blueprint.level_counts {
         if *want == 0 {
@@ -175,7 +175,7 @@ pub fn select(
         }
     }
 
-    // ------------------------------------------------------------ bonus items
+    // --- bonus items
     let mut bonus: Vec<String> = Vec::new();
     for (level, want) in &blueprint.bonus_counts {
         if *want == 0 {

src/cli.rs

@@ -412,6 +412,29 @@ pub(crate) enum ExportCommand {
         #[arg(long)]
         out: Option<PathBuf>,
     },
+    /// Write a Quarto worksheet and a matching solutions document.
+    ///
+    /// The worksheet holds the questions and nothing else; the solutions document
+    /// adds the key, the worked reasoning, the rubric, and the readings to revisit.
+    /// This is the path that does not go through Canvas, so a student can practice
+    /// from the `.qmd` and check themselves against the solutions. Render each with
+    /// `quarto render <file>.qmd`.
+    Practice {
+        /// Assessment id.
+        id: String,
+        /// Which form's ordering to use.
+        #[arg(long, default_value = "A")]
+        form: String,
+        /// Which documents to write; defaults to both. Values: worksheet, solutions.
+        #[arg(long, value_name = "DOC")]
+        variant: Vec<String>,
+        /// Output directory; defaults to build/.
+        #[arg(long)]
+        out: Option<PathBuf>,
+        /// Do not leave written-answer space after open-response questions.
+        #[arg(long)]
+        no_answer_space: bool,
+    },
 }
 
 #[derive(Debug, Subcommand)]

src/commands/export.rs

@@ -12,6 +12,7 @@
 use coursebank::assessment::Form;
 use coursebank::error::{Error, Result};
 use coursebank::layout::Layout;
+use coursebank::practice;
 use coursebank::qti;
 use coursebank::typst;
 use coursebank::yaml;
@@ -168,9 +169,65 @@ pub(crate) fn export(cli: &Cli, sub: &ExportCommand) -> Result<Outcome> {
             println!("wrote {}", path.display());
             Ok(Outcome::Ok)
         }
+        ExportCommand::Practice {
+            id,
+            form,
+            variant,
+            out,
+            no_answer_space,
+        } => {
+            let record = load_record(&catalog, id)?;
+            let form = pick_form(&record, form)?;
+            let dir = out.clone().unwrap_or(build);
+            for v in pick_practice_variants(variant)? {
+                let opts = practice::Options {
+                    form: form.clone(),
+                    variant: v,
+                    answer_space: !no_answer_space,
+                };
+                let text = practice::render(&catalog, &record, &opts)?;
+                let path = dir.join(format!("{id}-{}{}.qmd", form.id, v.suffix()));
+                yaml::write_text(&path, &text)?;
+                println!("wrote {}", path.display());
+            }
+            if !cli.quiet {
+                println!("\nRender with: quarto render <file>.qmd");
+            }
+            Ok(Outcome::Ok)
+        }
     }
 }
 
+/// Resolves the `--variant` flags for `export practice`, defaulting to both.
+///
+/// # Arguments
+///
+/// * `names` - the raw flag values, possibly empty.
+///
+/// # Returns
+///
+/// The documents to write, deduplicated and in canonical order (worksheet first).
+///
+/// # Errors
+///
+/// Returns [`Error::Usage`] naming the valid tokens.
+fn pick_practice_variants(names: &[String]) -> Result<Vec<practice::Variant>> {
+    if names.is_empty() {
+        return Ok(practice::Variant::ALL.to_vec());
+    }
+    let mut wanted = Vec::new();
+    for name in names {
+        let variant = practice::Variant::parse(name)?;
+        if !wanted.contains(&variant) {
+            wanted.push(variant);
+        }
+    }
+    Ok(practice::Variant::ALL
+        .into_iter()
+        .filter(|v| wanted.contains(v))
+        .collect())
+}
+
 /// Resolves the `--variant` flags, defaulting to every document.
 ///
 /// # Arguments

src/export.rs

@@ -8,6 +8,7 @@
 //! |:--|:--|:--|
 //! | [`qti`] | a QTI 1.2 zip | importing into Canvas |
 //! | [`typst`] | `.typ` source | a printed exam, answer key, and bubble sheet |
+//! | [`practice`] | Quarto Markdown | a worksheet and a solutions document, off Canvas |
 //! | [`report`] | Markdown and HTML | students, and yourself |
 //! | [`lecture`] | Markdown | the reading list on the course website |
 //!
@@ -22,6 +23,7 @@
 //! The instructor report answers "what should I fix?" and holds the item statistics.
 
 pub mod lecture;
+pub mod practice;
 pub mod qti;
 pub mod report;
 pub mod typst;

src/export/practice.rs

@@ -0,0 +1,669 @@
+// SPDX-License-Identifier: Prosperity-3.0.0
+// Copyright Scientific Computing Studio
+// Source: https://git.scient.ing/education/coursebank
+
+//! Rendering an assessment as a Quarto worksheet a student can work through, and
+//! a matching solutions document they can learn from.
+//!
+//! This is the path that does not go through Canvas. You assemble a homework,
+//! quiz, or practice set the same way you assemble an exam, then render it as two
+//! `.qmd` files: [`Variant::Worksheet`] holds the questions and nothing else, and
+//! [`Variant::Solutions`] holds the same questions with the key marked, the worked
+//! reasoning, the rubric for anything open-ended, and where to read again. A
+//! student with neither the Canvas quiz nor the printed exam can still practice
+//! from the worksheet and check themselves against the solutions.
+//!
+//! A worksheet never contains the answer. It is built only from stems and
+//! options, and the option letters are the printed positions, so the document has
+//! nothing in it to leak: not a `correct` flag, not a solution, not a rationale.
+//! [`Variant::Solutions`] is a separate render from the same input.
+//!
+//! Option order comes from the form's seed. When a form shuffles, both
+//! documents relabel to the printed order through
+//! [`select::option_order`], so a worksheet handed to
+//! a student who saw form B agrees with the form B solutions.
+//!
+//! Everything a solution shows is authored: the model answer, the explanation, the
+//! per-option notes, the rubric, and the review citations. Nothing is invented
+//! here. A question with an empty [`crate::item::Solution`] renders its key and
+//! stops, which is a visible cue to go finish writing it.
+
+use crate::assessment::{AssessmentFile, Form, Placement};
+use crate::catalog::Catalog;
+use crate::course::{CourseFile, Reference};
+use crate::error::Result;
+use crate::item::{Choice, Citation, Item};
+use crate::markup;
+use crate::select;
+
+/// Which of the two documents to render.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub enum Variant {
+    /// Questions only, for a student to work through.
+    #[default]
+    Worksheet,
+    /// Questions with the key, worked solutions, rubric, and readings.
+    Solutions,
+}
+
+impl Variant {
+    /// Both documents, in the order they are usually written.
+    pub const ALL: [Variant; 2] = [Variant::Worksheet, Variant::Solutions];
+
+    /// The token used on the command line and in a file name.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Variant::Worksheet => "worksheet",
+            Variant::Solutions => "solutions",
+        }
+    }
+
+    /// The suffix a generated file name carries, e.g. `-solutions`.
+    pub fn suffix(self) -> &'static str {
+        match self {
+            Variant::Worksheet => "",
+            Variant::Solutions => "-solutions",
+        }
+    }
+
+    /// The word for this document in a title.
+    fn title_word(self) -> &'static str {
+        match self {
+            Variant::Worksheet => "Questions",
+            Variant::Solutions => "Solutions",
+        }
+    }
+
+    /// Parses a `--variant` value.
+    ///
+    /// # Arguments
+    ///
+    /// * `name` - the token, case insensitive; `questions` is accepted for the
+    ///   worksheet and `key` for the solutions, since those are what people type.
+    ///
+    /// # Returns
+    ///
+    /// The variant.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`crate::error::Error::Usage`] naming the valid tokens.
+    pub fn parse(name: &str) -> Result<Variant> {
+        match name.trim().to_ascii_lowercase().as_str() {
+            "worksheet" | "questions" | "q" => Ok(Variant::Worksheet),
+            "solutions" | "solution" | "key" => Ok(Variant::Solutions),
+            other => Err(crate::error::Error::usage(format!(
+                "unknown practice document `{other}`; use worksheet or solutions"
+            ))),
+        }
+    }
+}
+
+/// What to render.
+#[derive(Debug, Clone)]
+pub struct Options {
+    /// Which form's ordering to use. Defaults to an unshuffled form.
+    pub form: Form,
+    /// Which document.
+    pub variant: Variant,
+    /// Leave vertical space after each question on the worksheet for a written
+    /// answer. Ignored for the solutions document.
+    pub answer_space: bool,
+}
+
+impl Default for Options {
+    fn default() -> Options {
+        Options {
+            form: Form {
+                id: "A".to_string(),
+                seed: 0,
+                shuffle_items: false,
+                shuffle_options: false,
+            },
+            variant: Variant::Worksheet,
+            answer_space: true,
+        }
+    }
+}
+
+impl Options {
+    /// Options for one variant on one form.
+    ///
+    /// # Arguments
+    ///
+    /// * `variant` - which document.
+    /// * `form` - the form whose ordering to use.
+    ///
+    /// # Returns
+    ///
+    /// The options, with the answer space on.
+    pub fn new(variant: Variant, form: Form) -> Options {
+        Options {
+            form,
+            variant,
+            answer_space: true,
+        }
+    }
+}
+
+/// Renders the questions-only worksheet.
+///
+/// # Arguments
+///
+/// * `catalog` - the loaded course.
+/// * `record` - the assessment record.
+/// * `form` - the form whose ordering to use.
+///
+/// # Returns
+///
+/// The Quarto Markdown, ending in a newline.
+///
+/// # Errors
+///
+/// Returns [`crate::error::Error::Unresolved`] when a placement references a
+/// missing item.
+pub fn worksheet(catalog: &Catalog, record: &AssessmentFile, form: &Form) -> Result<String> {
+    render(
+        catalog,
+        record,
+        &Options::new(Variant::Worksheet, form.clone()),
+    )
+}
+
+/// Renders the solutions document.
+///
+/// # Arguments
+///
+/// * `catalog` - the loaded course.
+/// * `record` - the assessment record.
+/// * `form` - the form whose ordering to use.
+///
+/// # Returns
+///
+/// The Quarto Markdown, ending in a newline.
+///
+/// # Errors
+///
+/// As [`worksheet`].
+pub fn solutions(catalog: &Catalog, record: &AssessmentFile, form: &Form) -> Result<String> {
+    render(
+        catalog,
+        record,
+        &Options::new(Variant::Solutions, form.clone()),
+    )
+}
+
+/// Renders one document.
+///
+/// # Arguments
+///
+/// * `catalog` - the loaded course.
+/// * `record` - the assessment record.
+/// * `opts` - what to render.
+///
+/// # Returns
+///
+/// The Quarto Markdown, ending in a newline.
+///
+/// # Errors
+///
+/// Returns [`crate::error::Error::Unresolved`] when a placement references a
+/// missing item.
+pub fn render(catalog: &Catalog, record: &AssessmentFile, opts: &Options) -> Result<String> {
+    let course = &catalog.course;
+    let mut out = front_matter(course, record, opts.variant);
+
+    if let Some(instructions) = &record.assessment.instructions {
+        out.push_str(&markup::to_markdown(instructions));
+        out.push_str("\n\n");
+    }
+
+    // One shared stimulus is printed once, above the first question that uses it,
+    // so a testlet reads as a block rather than repeating the vignette per item.
+    let mut printed_stimulus: Option<String> = None;
+
+    let layout = select::layout(record, &opts.form);
+    for (position, placement) in layout.iter().filter(|p| !p.dropped).enumerate() {
+        let entry = catalog.require(&placement.item)?;
+        let item = &entry.item;
+        let number = position + 1;
+
+        if let Some(stimulus_id) = &item.stimulus {
+            if printed_stimulus.as_deref() != Some(stimulus_id.as_str()) {
+                if let Some(stimulus) = course.stimuli.get(stimulus_id) {
+                    out.push_str("::: {.stimulus}\n\n");
+                    out.push_str(&markup::to_markdown(&stimulus.body));
+                    out.push_str("\n\n:::\n\n");
+                }
+                printed_stimulus = Some(stimulus_id.clone());
+            }
+        }
+
+        match opts.variant {
+            Variant::Worksheet => worksheet_question(
+                &mut out,
+                number,
+                placement,
+                item,
+                &opts.form,
+                opts.answer_space,
+            ),
+            Variant::Solutions => {
+                solution_question(&mut out, number, placement, item, &opts.form, course)
+            }
+        }
+    }
+
+    Ok(out)
+}
+
+/// The Quarto YAML front matter.
+fn front_matter(course: &CourseFile, record: &AssessmentFile, variant: Variant) -> String {
+    let title = format!("{}: {}", record.assessment.title, variant.title_word());
+    let subtitle = format!("{} · {}", course.course.code, course.course.title);
+    let mut out = String::from("---\n");
+    out.push_str(&format!("title: \"{}\"\n", yaml_quote(&title)));
+    out.push_str(&format!("subtitle: \"{}\"\n", yaml_quote(&subtitle)));
+    if let Some(date) = record.assessment.date {
+        out.push_str(&format!("date: \"{date}\"\n"));
+    }
+    out.push_str("format:\n  html:\n    toc: false\n    number-sections: false\n");
+    out.push_str("---\n\n");
+    out
+}
+
+/// One question on the worksheet: stem, options in printed order, no answer.
+fn worksheet_question(
+    out: &mut String,
+    number: usize,
+    placement: &Placement,
+    item: &Item,
+    form: &Form,
+    answer_space: bool,
+) {
+    out.push_str(&heading(number, placement));
+    out.push_str(&markup::to_markdown(&item.stem));
+    out.push_str("\n\n");
+
+    if item.has_options() {
+        let ordered = ordered_options(item, form, &placement.item);
+        for (position, source) in ordered.iter().enumerate() {
+            out.push_str(&format!(
+                "{}. {}\n",
+                letter(position),
+                markup::to_markdown(&source.text)
+            ));
+        }
+        out.push('\n');
+    } else if answer_space {
+        // A place to write, sized by the theme, present only when asked for.
+        out.push_str("::: {.answer-space}\n:::\n\n");
+    }
+}
+
+/// One question in the solutions document: stem, key, worked reasoning, rubric,
+/// and where to look again.
+fn solution_question(
+    out: &mut String,
+    number: usize,
+    placement: &Placement,
+    item: &Item,
+    form: &Form,
+    course: &CourseFile,
+) {
+    out.push_str(&heading(number, placement));
+    out.push_str(&meta_line(placement, item));
+    out.push_str(&markup::to_markdown(&item.stem));
+    out.push_str("\n\n");
+
+    if item.has_options() {
+        let ordered = ordered_options(item, form, &placement.item);
+        for (position, source) in ordered.iter().enumerate() {
+            let mark = if source.correct { " ✓" } else { "" };
+            let note = source
+                .student_text()
+                .map(|t| format!(": {}", markup::to_markdown(t)))
+                .unwrap_or_default();
+            out.push_str(&format!(
+                "{}. {}{mark}{note}\n",
+                letter(position),
+                markup::to_markdown(&source.text)
+            ));
+        }
+        out.push('\n');
+    }
+
+    solution_body(out, item);
+    objectives_line(out, item, course);
+    review_line(out, item, course);
+    out.push('\n');
+}
+
+/// The model answer, explanation, rubric, and accepted answers, when present.
+fn solution_body(out: &mut String, item: &Item) {
+    let Some(solution) = item.solution.as_ref().filter(|s| !s.is_empty()) else {
+        if !item.has_options() {
+            // An open-response question with no written solution is unfinished, and
+            // saying so in the document is more useful than a silent blank.
+            out.push_str("_No solution written yet._\n\n");
+        }
+        return;
+    };
+
+    if let Some(answer) = &solution.model_answer {
+        out.push_str(&format!(
+            "**Model answer.** {}\n\n",
+            markup::to_markdown(answer)
+        ));
+    }
+    if let Some(explanation) = &solution.explanation {
+        out.push_str(&markup::to_markdown(explanation));
+        out.push_str("\n\n");
+    }
+    if !solution.rubric.is_empty() {
+        out.push_str("**Rubric**\n\n");
+        for criterion in &solution.rubric {
+            let points = criterion
+                .points
+                .map(|p| format!(" ({} pt)", trim_number(p)))
+                .unwrap_or_default();
+            out.push_str(&format!(
+                "- {}{points}\n",
+                markup::to_markdown(&criterion.description)
+            ));
+        }
+        out.push('\n');
+    }
+    if !solution.accepted.is_empty() {
+        let joined: Vec<String> = solution
+            .accepted
+            .iter()
+            .map(|a| markup::to_markdown(a))
+            .collect();
+        out.push_str(&format!("**Accepted answers:** {}\n\n", joined.join("; ")));
+    }
+}
+
+/// The `Tests:` line naming the objectives this item measures.
+fn objectives_line(out: &mut String, item: &Item, course: &CourseFile) {
+    if item.learning_objectives.is_empty() {
+        return;
+    }
+    let texts: Vec<String> = item
+        .learning_objectives
+        .iter()
+        .map(|id| course.objective_text(id))
+        .collect();
+    out.push_str(&format!("**Tests:** {}\n\n", texts.join("; ")));
+}
+
+/// The `Review:` line, resolving each citation to a short label, linked when a URL
+/// resolves.
+fn review_line(out: &mut String, item: &Item, course: &CourseFile) {
+    let Some(solution) = item.solution.as_ref() else {
+        return;
+    };
+    if solution.review.is_empty() {
+        return;
+    }
+    let cites: Vec<String> = solution.review.iter().map(|c| cite(course, c)).collect();
+    out.push_str(&format!("**Review:** {}\n\n", cites.join("; ")));
+}
+
+/// Resolves one citation to Markdown, mirroring the lecture reading style
+/// `` `KKW` [§6.1](url) ``.
+fn cite(course: &CourseFile, citation: &Citation) -> String {
+    if let Some(text) = &citation.text {
+        if citation.reference.is_none() {
+            return text.clone();
+        }
+    }
+    let Some(key) = &citation.reference else {
+        return citation.display();
+    };
+    let Some(reference) = course.references.get(key) else {
+        return citation.display();
+    };
+    let label = reference.label.as_deref().unwrap_or(key);
+    let locator = citation.locator.as_deref().unwrap_or("");
+    match resolve_url(citation, reference) {
+        Some(url) if !locator.is_empty() => format!("`{label}` [{locator}]({url})"),
+        Some(url) => format!("`{label}` [{}]({url})", reference.title),
+        None if !locator.is_empty() => format!("`{label}` {locator}"),
+        None => format!("`{label}`"),
+    }
+}
+
+/// The URL for a citation: its own `url`, else the reference `base_url` joined with
+/// the citation `path`.
+fn resolve_url(citation: &Citation, reference: &Reference) -> Option<String> {
+    if let Some(url) = &citation.url {
+        return Some(url.clone());
+    }
+    let path = citation.path.as_deref()?;
+    let base = reference.base_url.as_deref()?;
+    Some(match (base.ends_with('/'), path.starts_with('/')) {
+        (true, true) => format!("{base}{}", &path[1..]),
+        (false, false) => format!("{base}/{path}"),
+        _ => format!("{base}{path}"),
+    })
+}
+
+/// The `## Question N` heading, marking a bonus item.
+fn heading(number: usize, placement: &Placement) -> String {
+    let bonus = if placement.bonus { " (bonus)" } else { "" };
+    format!("## Question {number}{bonus}\n\n")
+}
+
+/// The italic level-and-points line under a solutions heading.
+fn meta_line(placement: &Placement, item: &Item) -> String {
+    let level = placement.level.unwrap_or(item.level);
+    let mut parts = vec![format!("Level {} ({})", level.code(), level.name())];
+    if let Some(points) = placement.points {
+        parts.push(format!("{} point(s)", trim_number(points)));
+    }
+    format!("_{}_\n\n", parts.join(" · "))
+}
+
+/// The options in the order the form prints them.
+///
+/// Salted with the item's global id, the same value the Typst and QTI exports use,
+/// so a worksheet built for form B lists options in the order that form's paper and
+/// its Canvas quiz do.
+fn ordered_options<'a>(item: &'a Item, form: &Form, uid: &str) -> Vec<&'a Choice> {
+    select::option_order(form, uid, item.options.len())
+        .into_iter()
+        .map(|i| &item.options[i])
+        .collect()
+}
+
+/// The printed letter for a zero-based position.
+fn letter(position: usize) -> char {
+    (b'A' + (position as u8 % 26)) as char
+}
+
+/// Formats a point value without a trailing `.0`.
+fn trim_number(value: f64) -> String {
+    if value.fract() == 0.0 {
+        format!("{}", value as i64)
+    } else {
+        let s = format!("{value:.2}");
+        s.trim_end_matches('0').trim_end_matches('.').to_string()
+    }
+}
+
+/// Escapes a double quote for a YAML double-quoted scalar.
+fn yaml_quote(s: &str) -> String {
+    s.replace('\\', "\\\\").replace('"', "\\\"")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assessment::{Assessment, Kind, Platform};
+
+    /// Writes a course and a bank to a temp directory and loads them, the same way
+    /// the catalog tests do, so this exercises only public API. The `tag` keeps each
+    /// test in its own directory, so tests running in parallel do not clobber a
+    /// shared `course.yaml`.
+    fn catalog(tag: &str) -> Catalog {
+        let dir = std::env::temp_dir().join(format!("cb-practice-{tag}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(dir.join("banks")).unwrap();
+        std::fs::write(
+            dir.join("course.yaml"),
+            r#"
+course: { code: BIOSC 1000, title: Biochemistry, term: 2026f }
+references:
+  kkw:
+    label: KKW
+    title: The molecules of life
+    base_url: https://example.org/kkw/
+lectures:
+  L1.1: { title: Enthalpy }
+learning_objectives:
+  lo-enthalpy:
+    text: Define enthalpy and explain the constant-pressure result.
+    lectures: [L1.1]
+    order: 1
+"#,
+        )
+        .unwrap();
+        std::fs::write(
+            dir.join("banks").join("l11.yaml"),
+            r#"
+bank: { id: l11, title: L1.1 }
+items:
+  - id: q-enthalpy-001
+    status: draft
+    level: 1
+    stem: At constant pressure, the heat exchanged equals which quantity?
+    learning_objectives: [lo-enthalpy]
+    options:
+      - { id: A, text: "the enthalpy change", correct: true, feedback_student: "Right: P dV work is folded into H." }
+      - { id: B, text: "the internal energy change", misconception: "ignores expansion work" }
+      - { id: C, text: "zero" }
+    solution:
+      explanation: "Because H = U + PV, at constant P the P dV term is the expansion work, so q_p equals the change in H."
+      review:
+        - { ref: kkw, locator: "§6.4", path: "6/A/#4" }
+  - id: q-enthalpy-op-001
+    status: draft
+    level: 2
+    format: open_response
+    stem: Explain why, at constant pressure, the heat exchanged equals the enthalpy change.
+    learning_objectives: [lo-enthalpy]
+    solution:
+      model_answer: "At constant pressure the P dV expansion work is folded into H = U + PV, so q_p is the change in H."
+      rubric:
+        - { description: "states H = U + PV", points: 1 }
+        - { description: "identifies q_p with the enthalpy change", points: 1 }
+      review:
+        - { ref: kkw, locator: "§6.4", path: "6/A/#4" }
+"#,
+        )
+        .unwrap();
+        Catalog::load(&dir).expect("catalog loads")
+    }
+
+    fn record() -> AssessmentFile {
+        AssessmentFile {
+            schema_version: "1.0".into(),
+            assessment: Assessment {
+                id: "hw-1".into(),
+                title: "Homework 1".into(),
+                term: None,
+                kind: Kind::Homework,
+                date: None,
+                platform: Platform::Canvas,
+                minutes_allowed: None,
+                attempts: None,
+                shuffle: None,
+                scoring_policy: None,
+                instructions: None,
+                notes: None,
+            },
+            blueprint: None,
+            forms: Vec::new(),
+            items: vec![
+                Placement {
+                    number: 1,
+                    item: "l11::q-enthalpy-001".into(),
+                    version: None,
+                    fingerprint: None,
+                    points: Some(1.0),
+                    bonus: false,
+                    key: vec!["A".into()],
+                    level: None,
+                    learning_objectives: Vec::new(),
+                    credit_overrides: Default::default(),
+                    dropped: false,
+                },
+                Placement {
+                    number: 2,
+                    item: "l11::q-enthalpy-op-001".into(),
+                    version: None,
+                    fingerprint: None,
+                    points: Some(2.0),
+                    bonus: false,
+                    key: Vec::new(),
+                    level: None,
+                    learning_objectives: Vec::new(),
+                    credit_overrides: Default::default(),
+                    dropped: false,
+                },
+            ],
+        }
+    }
+
+    #[test]
+    fn worksheet_withholds_the_answer() {
+        let md =
+            worksheet(&catalog("worksheet"), &record(), &Options::default().form).expect("renders");
+        assert!(md.contains("## Question 1"));
+        assert!(md.contains("A. the enthalpy change"));
+        // Nothing that reveals the key or the reasoning.
+        assert!(!md.contains('✓'), "no check marks on the worksheet:\n{md}");
+        assert!(!md.contains("Model answer"), "no model answer:\n{md}");
+        assert!(!md.contains("P dV"), "no explanation:\n{md}");
+        assert!(!md.contains("Rubric"));
+        // The open-response question leaves room to write.
+        assert!(md.contains("answer-space"));
+    }
+
+    #[test]
+    fn solutions_show_key_reasoning_rubric_and_review() {
+        let md =
+            solutions(&catalog("solutions"), &record(), &Options::default().form).expect("renders");
+        assert!(md.contains("A. the enthalpy change ✓"));
+        assert!(md.contains("the internal energy change: ignores expansion work"));
+        assert!(md.contains("**Model answer.**"));
+        assert!(md.contains("H = U + PV"));
+        assert!(md.contains("**Rubric**"));
+        assert!(md.contains("states H = U + PV (1 pt)"));
+        assert!(md.contains("Tests:** Define enthalpy"));
+        // The review citation resolves to the label and a link.
+        assert!(
+            md.contains("`KKW` [§6.4](https://example.org/kkw/6/A/#4)"),
+            "{md}"
+        );
+    }
+
+    #[test]
+    fn front_matter_titles_each_document() {
+        let ws = worksheet(
+            &catalog("front-matter-ws"),
+            &record(),
+            &Options::default().form,
+        )
+        .expect("renders");
+        assert!(ws.contains("title: \"Homework 1: Questions\""));
+        let sol = solutions(
+            &catalog("front-matter-sol"),
+            &record(),
+            &Options::default().form,
+        )
+        .expect("renders");
+        assert!(sol.contains("title: \"Homework 1: Solutions\""));
+    }
+}

src/export/qti.rs

@@ -47,9 +47,9 @@ const IMSMD_NS: &str = "http://www.imsglobal.org/xsd/imsmd_v1p2";
 const IMSCP_SCHEMA: &str = "http://www.imsglobal.org/xsd/imscp_v1p1 imscp_v1p1.xsd \
                             http://www.imsglobal.org/xsd/imsmd_v1p2 imsmd_v1p2p2.xsd";
 
-// ---------------------------------------------------------------------------
+// ---
 // A very small XML tree
-// ---------------------------------------------------------------------------
+// ---
 
 /// One XML element.
 #[derive(Debug, Clone)]
@@ -155,9 +155,9 @@ fn escape_attr(s: &str) -> String {
     escape_text(s).replace('"', """)
 }
 
-// ---------------------------------------------------------------------------
+// ---
 // Package construction
-// ---------------------------------------------------------------------------
+// ---
 
 /// Options for a QTI export.
 #[derive(Debug, Clone)]
@@ -338,6 +338,11 @@ pub fn build(catalog: &Catalog, record: &AssessmentFile, opts: &QtiOptions) -> R
 ///
 /// The element.
 fn build_item(assessment_id: &str, uid: &str, item: &Item, points: f64, opts: &QtiOptions) -> Node {
+    // An open-response item is an essay in Canvas: no choices, graded by hand.
+    if !item.format.has_options() {
+        return build_essay_item(assessment_id, uid, item, points, opts);
+    }
+
     let order = select::option_order(&opts.form, uid, item.options.len());
     let ordered: Vec<&crate::item::Choice> = order.iter().map(|i| &item.options[*i]).collect();
 
@@ -499,6 +504,104 @@ fn build_item(assessment_id: &str, uid: &str, item: &Item, points: f64, opts: &Q
     node
 }
 
+/// Builds a Canvas essay item for an open-response question.
+///
+/// An essay has no choices and no automatic score: the `<other/>` condition leaves
+/// grading to the instructor. When feedback is on and a model answer exists, it
+/// rides along as general feedback so a student sees it after submitting.
+///
+/// This mapping has not been round-tripped through a live Canvas import in this
+/// build, so verify it against your instance before relying on it for a graded
+/// quiz.
+///
+/// # Arguments
+///
+/// * `assessment_id` - salts the generated ids.
+/// * `uid` - the item's global id.
+/// * `item` - the item.
+/// * `points` - points as administered.
+/// * `opts` - export options.
+///
+/// # Returns
+///
+/// The element.
+fn build_essay_item(
+    assessment_id: &str,
+    uid: &str,
+    item: &Item,
+    points: f64,
+    opts: &QtiOptions,
+) -> Node {
+    let item_meta = Node::new("itemmetadata").child(Node::new("qtimetadata").children(vec![
+        metadata_field("question_type", item.format.qti_type()),
+        metadata_field("points_possible", &format!("{points:.2}")),
+        metadata_field("assessment_question_identifierref", &qti_id(uid)),
+    ]));
+
+    let presentation = Node::new("presentation")
+        .child(mattext(&format!(
+            "<div>{}</div>",
+            markup::to_html(&item.stem)
+        )))
+        .child(
+            Node::new("response_str")
+                .attr("ident", "response1")
+                .attr("rcardinality", "Single")
+                .child(
+                    Node::new("render_fib").child(
+                        Node::new("response_label")
+                            .attr("ident", "answer1")
+                            .attr("rshuffle", "No"),
+                    ),
+                ),
+        );
+
+    // The model answer, shown as general feedback after submission.
+    let model = item
+        .solution
+        .as_ref()
+        .and_then(|s| s.model_answer.as_deref())
+        .filter(|_| opts.include_feedback);
+
+    let mut condition = Node::new("respcondition")
+        .attr("continue", "No")
+        .child(Node::new("conditionvar").child(Node::new("other")));
+    if model.is_some() {
+        condition = condition.child(
+            Node::new("displayfeedback")
+                .attr("feedbacktype", "Response")
+                .attr("linkrefid", "general_fb"),
+        );
+    }
+
+    let resprocessing = Node::new("resprocessing")
+        .child(
+            Node::new("outcomes").child(
+                Node::new("decvar")
+                    .attr("maxvalue", "100")
+                    .attr("minvalue", "0")
+                    .attr("varname", "SCORE")
+                    .attr("vartype", "Decimal"),
+            ),
+        )
+        .child(condition);
+
+    let mut node = Node::new("item")
+        .attr("ident", qti_id(&format!("{assessment_id}/{uid}")))
+        .attr("title", item.display_title())
+        .child(item_meta)
+        .child(presentation)
+        .child(resprocessing);
+
+    if let Some(text) = model {
+        node = node.child(Node::new("itemfeedback").attr("ident", "general_fb").child(
+            Node::new("flow_mat").child(mattext(&format!("<div>{}</div>", markup::to_html(text)))),
+        ));
+    }
+
+    node
+}
+
 /// A `<material><mattext texttype="text/html">` pair.
 ///
 /// # Arguments

src/export/report.rs

@@ -98,7 +98,7 @@ pub fn student(
     ));
     out.push_str(&format!("**{}**\n\n", summary.display_name()));
 
-    // ---------------------------------------------------------------- score
+    // --- score
     out.push_str(&format!(
         "You scored **{:.1} of {:.1} points ({:.0}%)**",
         summary.points, summary.points_possible, summary.percent
@@ -144,7 +144,7 @@ pub fn student(
         }
     }
 
-    // ----------------------------------------------------------- objectives
+    // --- objectives
     if opts.objectives && !summary.objectives.is_empty() {
         out.push_str("## What this exam says about each learning objective\n\n");
         out.push_str("| | Objective | You | Class | Items |\n|:--|:--|--:|--:|--:|\n");
@@ -180,7 +180,7 @@ pub fn student(
         }
     }
 
-    // --------------------------------------------------------------- levels
+    // --- levels
     if opts.levels && summary.levels.len() > 1 {
         out.push_str("## Kinds of thinking\n\n");
         out.push_str(
@@ -231,7 +231,7 @@ pub fn student(
         }
     }
 
-    // ---------------------------------------------------------- what to do
+    // --- what to do
     if !summary.focus.is_empty() {
         out.push_str("## Where to put your time\n\n");
         out.push_str("In this order:\n\n");
@@ -274,7 +274,7 @@ pub fn student(
         out.push_str(&format!("You have clearly got {}.\n\n", list(&refs)));
     }
 
-    // --------------------------------------------------------- missed items
+    // --- missed items
     if opts.missed && !summary.missed.is_empty() {
         out.push_str("## Question by question\n\n");
         out.push_str(
@@ -356,7 +356,7 @@ pub fn cohort(
             .unwrap_or_else(|| "date not recorded".into())
     ));
 
-    // ------------------------------------------------------------- summary
+    // --- summary
     let r = &analysis.reliability;
     out.push_str("## Summary\n\n");
     out.push_str(&format!(
@@ -408,7 +408,7 @@ pub fn cohort(
         out.push_str(&format!("> {w}\n\n"));
     }
 
-    // ------------------------------------------------------- revise queue
+    // --- revise queue
     let queue = analysis.revise_queue();
     out.push_str("## What to revise\n\n");
     if queue.is_empty() {
@@ -477,7 +477,7 @@ pub fn cohort(
         }
     }
 
-    // ---------------------------------------------------------- item table
+    // --- item table
     out.push_str("## Every item\n\n");
     out.push_str(
         "| Q | Item | Lv | p | r | D | Blank | Flags |\n|--:|:--|--:|--:|--:|--:|--:|:--|\n",
@@ -535,7 +535,7 @@ pub fn cohort(
         }
     }
 
-    // -------------------------------------------------------- class gaps
+    // --- class gaps
     out.push_str("## Objectives the class did not meet\n\n");
     if cohort.class_gaps.is_empty() {
         out.push_str("Every assessed objective cleared the mastery threshold.\n\n");
@@ -556,7 +556,7 @@ pub fn cohort(
         out.push('\n');
     }
 
-    // ------------------------------------------------------ level coverage
+    // --- level coverage
     out.push_str("## Coverage and class performance by level\n\n");
     let counts = record.level_counts();
     out.push_str("| Level | Items | Class rate |\n|:--|--:|--:|\n");
@@ -587,7 +587,7 @@ pub fn cohort(
         let _ = bp;
     }
 
-    // -------------------------------------------------------- archetypes
+    // --- archetypes
     if !cohort.archetypes.is_empty() {
         out.push_str("## Patterns across students\n\n");
         out.push_str(

src/export/typst/payload.rs

@@ -662,11 +662,7 @@ fn calibration(item: &Item) -> Option<BTreeMap<String, f64>> {
 
 /// The token for a response format.
 fn format_token(format: Format) -> &'static str {
-    match format {
-        Format::SingleBestAnswer => "single_best_answer",
-        Format::MultipleResponse => "multiple_response",
-        Format::TrueFalse => "true_false",
-    }
+    format.as_str()
 }
 
 /// The token for an administration platform.

src/lib.rs

@@ -110,7 +110,7 @@ pub use data::{canvas, gradescope, responses, store};
 
 pub use analysis::{calibrate, classical, irt, students};
 
-pub use export::{lecture, qti, report, typst};
+pub use export::{lecture, practice, qti, report, typst};
 
 pub use catalog::Catalog;
 pub use course::{CourseFile, SCHEMA_VERSION};

src/model/bank.rs

@@ -352,10 +352,20 @@ fn validate_item(
         issues.push("version must be at least 1".into());
     }
 
-    // --- options -----------------------------------------------------------
-    if it.options.len() < 2 {
+    // --- options ---
+    // An open-response item takes no options; its answer lives in `solution`.
+    // Every other format needs at least two things to choose between.
+    if it.format.has_options() {
+        if it.options.len() < 2 {
+            issues.push(format!(
+                "needs at least 2 options, has {}",
+                it.options.len()
+            ));
+        }
+    } else if !it.options.is_empty() {
         issues.push(format!(
-            "needs at least 2 options, has {}",
+            "{} items take no options, but {} were given; put the answer in `solution`",
+            it.format.as_str(),
             it.options.len()
         ));
     }
@@ -418,7 +428,7 @@ fn validate_item(
         }
     }
 
-    // --- key ---------------------------------------------------------------
+    // --- key -----
     let keys = it.key_indices();
     match it.format {
         Format::SingleBestAnswer => {
@@ -448,9 +458,14 @@ fn validate_item(
                 issues.push("true_false needs exactly one keyed option".into());
             }
         }
+        Format::OpenResponse => {
+            if !keys.is_empty() {
+                issues.push("open_response items have no keyed option".into());
+            }
+        }
     }
 
-    // --- level and process must agree -------------------------------------
+    // --- level and process must agree --------
     if let Some(p) = it.cognitive_process {
         if !it.level.allows(p) {
             issues.push(format!(
@@ -461,7 +476,7 @@ fn validate_item(
         }
     }
 
-    // --- design plausibility ----------------------------------------------
+    // --- design plausibility -----------
     if let Some(d) = &it.design {
         if let Some(x) = d.expected_difficulty {
             if !(0.0..=1.0).contains(&x) {
@@ -479,7 +494,7 @@ fn validate_item(
         }
     }
 
-    // --- calibration plausibility -----------------------------------------
+    // --- calibration plausibility ------
     if let Some(c) = &it.calibration {
         if let Some(p) = c.p_value {
             if !(0.0..=1.0).contains(&p) {
@@ -514,7 +529,7 @@ fn validate_item(
         }
     }
 
-    // --- history must be coherent -----------------------------------------
+    // --- history must be coherent ------
     let mut last_version = 0u32;
     for (i, h) in it.history.iter().enumerate() {
         if h.version <= last_version {
@@ -533,7 +548,7 @@ fn validate_item(
         ));
     }
 
-    // --- retirement -------------------------------------------------------
+    // --- retirement ----
     if it.retired.is_some() && it.status != Status::Retired {
         issues.push(format!(
             "has a `retired` block but status is `{}`",
@@ -541,7 +556,7 @@ fn validate_item(
         ));
     }
 
-    // --- approval gate ----------------------------------------------------
+    // --- approval gate -------
     // Approval is what permits an item onto a graded assessment, so it is the
     // right place to require that the item is fully sourced and designed.
     if it.status == Status::Approved {
@@ -557,9 +572,23 @@ fn validate_item(
         if it.design.is_none() {
             issues.push("approved items must carry a design block".into());
         }
+        // An open-response item is graded from its solution, so approving one with
+        // neither a model answer nor a rubric would leave nothing to mark it by.
+        if !it.format.has_options() {
+            let gradeable = it
+                .solution
+                .as_ref()
+                .is_some_and(|s| s.model_answer.is_some() || !s.rubric.is_empty());
+            if !gradeable {
+                issues.push(
+                    "approved open_response items need a solution with a model_answer or a rubric"
+                        .into(),
+                );
+            }
+        }
     }
 
-    // --- cross-file references --------------------------------------------
+    // --- cross-file references ---------
     if let Some(c) = course {
         for lo in &it.learning_objectives {
             match c.learning_objectives.get(lo) {
@@ -592,6 +621,15 @@ fn validate_item(
                 issues.push(format!("unknown stimulus `{st}`"));
             }
         }
+        // A citation that names a reference key must name a real one, so a review
+        // pointer in the solutions document never resolves to nothing.
+        for citation in it.solution.iter().flat_map(|s| &s.review) {
+            if let Some(key) = &citation.reference {
+                if !c.references.contains_key(key) {
+                    issues.push(format!("solution.review cites unknown reference `{key}`"));
+                }
+            }
+        }
         if let Some(floor) = c.policy.partial_credit_floor_level {
             for o in &it.options {
                 if o.is_partial() && it.level < floor {
@@ -644,6 +682,53 @@ mod tests {
         assert!(b.validate(None).is_empty(), "{:?}", b.validate(None));
     }
 
+    #[test]
+    fn open_response_validates_without_options_and_rejects_them() {
+        // No options is fine, and no key is required.
+        let ok = bank(
+            r#"
+  - id: q-a-op-001
+    status: draft
+    level: 2
+    format: open_response
+    stem: Explain the first law.
+    solution:
+      model_answer: Energy is conserved.
+"#,
+        );
+        assert!(ok.validate(None).is_empty(), "{:?}", ok.validate(None));
+
+        // Giving an open-response item options is the mistake, and so is approving
+        // one with nothing to grade it by.
+        let bad = bank(
+            r#"
+  - id: q-a-op-002
+    status: approved
+    level: 2
+    format: open_response
+    cognitive_process: explain
+    learning_objectives: [lo-x]
+    sources: [{ lecture: L1.1 }]
+    design: { rationale: r }
+    stem: Explain the first law.
+    options:
+      - { id: A, text: a, correct: true }
+      - { id: B, text: b }
+"#,
+        );
+        let issues = bad.validate(None);
+        assert!(
+            issues.iter().any(|i| i.contains("take no options")),
+            "{issues:?}"
+        );
+        assert!(
+            issues
+                .iter()
+                .any(|i| i.contains("model_answer or a rubric")),
+            "{issues:?}"
+        );
+    }
+
     #[test]
     fn catches_missing_and_multiple_keys() {
         let b = bank(

src/model/item.rs

@@ -19,7 +19,11 @@
 //! it. That keeps bank files readable and reviewable in a pull request while
 //! still letting statistics accumulate across terms.
 
-use serde::{Deserialize, Serialize};
+use std::fmt;
+
+use serde::de::{self, MapAccess, Visitor};
+use serde::ser::SerializeMap;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use crate::date::Date;
 use crate::hash::fingerprint;
@@ -79,8 +83,25 @@ pub struct Item {
 
     /// The answer options in canonical order. Shuffling happens at export time
     /// per form, never here, so the bank stays diffable.
+    ///
+    /// Empty for a [`Format::OpenResponse`] item, which is answered in free text
+    /// and graded from its [`Solution`] instead. A choice format must still supply
+    /// at least two, which [`crate::bank::BankFile::validate`] enforces; leaving
+    /// them out is reported there, with every other problem, rather than failing
+    /// the parse on its own.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub options: Vec<Choice>,
 
+    /// The worked solution: a model answer, an explanation a student can learn
+    /// from, and, for an open-response item, the rubric it is graded against.
+    ///
+    /// This is what the solutions document renders and what a paper answer key
+    /// prints. It is withheld from any question paper and from the exam payload,
+    /// the same way an option's `correct` flag is, so a document built for the
+    /// student cannot leak it.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub solution: Option<Solution>,
+
     /// Objectives this item measures, as ids into the course registry.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub learning_objectives: Vec<String>,
@@ -239,6 +260,214 @@ pub struct Source {
     pub recording_seconds: Option<u32>,
 }
 
+/// A pointer from an item into the course reference registry: where to read more,
+/// or what to revisit after missing the item.
+///
+/// It holds a citation key and a locator rather than a restated citation, so a
+/// reference is written once in `course.yaml` and a changed edition is a single
+/// edit. The exporters resolve it against
+/// [`crate::course::CourseFile::references`] into a short label such as `KKW §6.1`,
+/// linked when the location resolves to a URL. This is the same pointer a lecture
+/// [`crate::course::Reading`] uses, kept lean here because an item cites a reading;
+/// it does not restate one.
+///
+/// A citation may also be written as a bare string, which lands unparsed in `text`
+/// and serializes back out as a string, so a bank that stored readings as plain
+/// strings keeps loading and round-trips byte-for-byte.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct Citation {
+    /// Citation key into the course reference registry.
+    pub reference: Option<String>,
+    /// Where inside the work: `§6.1`, `pp. 212-219`, `fig. 4`.
+    pub locator: Option<String>,
+    /// Appended to the reference's `base_url` to reach this location.
+    pub path: Option<String>,
+    /// A full URL, when the location is not under the reference's `base_url`.
+    pub url: Option<String>,
+    /// A citation written as a bare string, held unparsed.
+    pub text: Option<String>,
+}
+
+impl Citation {
+    /// A short display string that needs no reference lookup.
+    ///
+    /// Prefers the unparsed `text`, then the key and locator. A caller that holds
+    /// the course, such as an exporter, can resolve a nicer label and a link; this
+    /// is the fallback for one that does not.
+    ///
+    /// # Returns
+    ///
+    /// The display string, empty when the citation carries nothing.
+    pub fn display(&self) -> String {
+        if let Some(text) = &self.text {
+            return text.clone();
+        }
+        match (&self.reference, &self.locator) {
+            (Some(k), Some(l)) => format!("{k} {l}"),
+            (Some(k), None) => k.clone(),
+            (None, Some(l)) => l.clone(),
+            (None, None) => String::new(),
+        }
+    }
+}
+
+/// Writes a citation as a mapping, or as a bare string when that is all it holds.
+impl Serialize for Citation {
+    fn serialize<S: Serializer>(&self, s: S) -> std::result::Result<S::Ok, S::Error> {
+        if let Some(text) = &self.text {
+            if self.reference.is_none()
+                && self.locator.is_none()
+                && self.path.is_none()
+                && self.url.is_none()
+            {
+                return s.serialize_str(text);
+            }
+        }
+        let mut map = s.serialize_map(None)?;
+        if let Some(v) = &self.reference {
+            map.serialize_entry("ref", v)?;
+        }
+        if let Some(v) = &self.locator {
+            map.serialize_entry("locator", v)?;
+        }
+        if let Some(v) = &self.path {
+            map.serialize_entry("path", v)?;
+        }
+        if let Some(v) = &self.url {
+            map.serialize_entry("url", v)?;
+        }
+        if let Some(v) = &self.text {
+            map.serialize_entry("text", v)?;
+        }
+        map.end()
+    }
+}
+
+/// Accepts a citation written either as a mapping or as a bare string.
+impl<'de> Deserialize<'de> for Citation {
+    fn deserialize<D: Deserializer<'de>>(d: D) -> std::result::Result<Citation, D::Error> {
+        /// The mapping form, with the field set kept in one place.
+        #[derive(Deserialize)]
+        #[serde(deny_unknown_fields)]
+        struct Mapping {
+            #[serde(rename = "ref", default)]
+            reference: Option<String>,
+            #[serde(default)]
+            locator: Option<String>,
+            #[serde(default)]
+            path: Option<String>,
+            #[serde(default)]
+            url: Option<String>,
+            #[serde(default)]
+            text: Option<String>,
+        }
+
+        struct V;
+        impl<'a> Visitor<'a> for V {
+            type Value = Citation;
+
+            fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.write_str("a citation mapping with a `ref`, or a plain citation string")
+            }
+
+            fn visit_str<E: de::Error>(self, v: &str) -> std::result::Result<Citation, E> {
+                Ok(Citation {
+                    text: Some(v.to_string()),
+                    ..Citation::default()
+                })
+            }
+
+            fn visit_map<M: MapAccess<'a>>(
+                self,
+                map: M,
+            ) -> std::result::Result<Citation, M::Error> {
+                let m = Mapping::deserialize(de::value::MapAccessDeserializer::new(map))?;
+                Ok(Citation {
+                    reference: m.reference,
+                    locator: m.locator,
+                    path: m.path,
+                    url: m.url,
+                    text: m.text,
+                })
+            }
+        }
+        d.deserialize_any(V)
+    }
+}
+
+/// One line of a grading rubric for an open-response item.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct RubricCriterion {
+    /// What earns the points, e.g. "states H = U + PV" or "compares to ~2.5 kJ/mol".
+    pub description: String,
+    /// Points for this line. Absent lets a grader decide; when present, the lines
+    /// are meant to sum to the item's point value.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub points: Option<f64>,
+}
+
+/// The worked solution to an item: what the answer is, why, and how it is graded.
+///
+/// One place, versioned with the question, holds everything a student learns from
+/// after the fact and everything a grader marks an open response against. For a
+/// choice item the per-option [`Choice::explanation`] says why each option is right
+/// or wrong; the solution adds the single worked line of reasoning a solutions
+/// document leads with. For an [`Format::OpenResponse`] item the solution is the
+/// whole answer, because there are no options to annotate.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct Solution {
+    /// The model answer, in the authoring markup. For an open-response item this is
+    /// the response a full-credit student would write; for a choice item it is an
+    /// optional one-line statement of the key in words.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub model_answer: Option<String>,
+    /// The worked reasoning a student can learn from: the derivation, the estimate,
+    /// the argument for the key over its neighbours. This is the body of the
+    /// solutions document.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub explanation: Option<String>,
+    /// How an open response is graded, one criterion per line.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub rubric: Vec<RubricCriterion>,
+    /// Responses a short constructed answer would be accepted as. Shown in the
+    /// solutions document as accepted answers, and the hook for automated grading
+    /// later.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub accepted: Vec<String>,
+    /// Where to look again after missing this item, as citations into the course
+    /// reference registry. Resolved and linked by the exporters.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub review: Vec<Citation>,
+}
+
+impl Solution {
+    /// Whether the solution carries anything worth rendering.
+    ///
+    /// Used to decide whether a solutions entry has a body to print, so an item
+    /// with an empty `solution:` block is treated as having none.
+    pub fn is_empty(&self) -> bool {
+        self.model_answer.is_none()
+            && self.explanation.is_none()
+            && self.rubric.is_empty()
+            && self.accepted.is_empty()
+            && self.review.is_empty()
+    }
+
+    /// Total of the rubric line points, when every line carries one.
+    ///
+    /// # Returns
+    ///
+    /// The sum, or `None` if any line omits its points or the rubric is empty.
+    pub fn rubric_points(&self) -> Option<f64> {
+        if self.rubric.is_empty() {
+            return None;
+        }
+        self.rubric.iter().map(|c| c.points).sum::<Option<f64>>()
+    }
+}
+
 /// A figure or data file reproduced with an item.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(deny_unknown_fields)]
@@ -473,6 +702,7 @@ impl Item {
             stimulus: None,
             stem: stem.to_string(),
             options,
+            solution: None,
             learning_objectives: Vec::new(),
             sources: Vec::new(),
             topics: Vec::new(),
@@ -538,6 +768,14 @@ impl Item {
         self.key_indices().len() > 1
     }
 
+    /// Whether the item presents selectable options, per its [`Format`].
+    ///
+    /// `false` for an [`Format::OpenResponse`] item. Callers that would otherwise
+    /// index `options` or read a key should branch on this first.
+    pub fn has_options(&self) -> bool {
+        self.format.has_options()
+    }
+
     /// The display title, falling back to a truncated stem.
     ///
     /// # Returns
@@ -821,4 +1059,77 @@ options:
             IrtModel::ThreePl
         );
     }
+
+    #[test]
+    fn open_response_item_parses_without_options() {
+        let it = item(
+            r#"
+id: q-enthalpy-op-001
+status: draft
+level: 2
+format: open_response
+stem: Explain why, at constant pressure, the heat exchanged equals the enthalpy change.
+solution:
+  model_answer: >-
+    At constant pressure the P dV expansion work is folded into H = U + PV, so the
+    heat q_p equals the change in H.
+  rubric:
+    - { description: "states H = U + PV", points: 1 }
+    - { description: "identifies q_p with the enthalpy change", points: 1 }
+  review:
+    - { ref: kuriyan2012molecules, locator: "§6.4", path: "6/A/#4" }
+"#,
+        );
+        assert_eq!(it.format, Format::OpenResponse);
+        assert!(it.options.is_empty());
+        assert!(!it.has_options());
+        assert!(it.key_letters().is_empty());
+        let sol = it.solution.as_ref().expect("has a solution");
+        assert!(!sol.is_empty());
+        assert_eq!(sol.rubric_points(), Some(2.0));
+        assert_eq!(sol.review.len(), 1);
+        assert_eq!(
+            sol.review[0].reference.as_deref(),
+            Some("kuriyan2012molecules")
+        );
+    }
+
+    #[test]
+    fn a_solution_serializes_only_what_it_holds() {
+        let it = item(
+            r#"
+id: q-demo-op-002
+status: draft
+level: 2
+format: open_response
+stem: State the first law.
+solution:
+  model_answer: The total energy of an isolated system is constant.
+"#,
+        );
+        let yaml = serde_yaml_ng::to_string(&it).expect("serializes");
+        // Open-response items carry no options key, and an empty rubric is omitted.
+        assert!(!yaml.contains("options:"), "no options key:\n{yaml}");
+        assert!(!yaml.contains("rubric"), "empty rubric omitted:\n{yaml}");
+        assert!(yaml.contains("model_answer:"));
+    }
+
+    #[test]
+    fn a_citation_round_trips_as_string_or_mapping() {
+        // A bare string stays a bare string.
+        let bare: Citation = serde_yaml_ng::from_str("\"KKW §6.4 (course reserve)\"").unwrap();
+        assert_eq!(bare.text.as_deref(), Some("KKW §6.4 (course reserve)"));
+        assert_eq!(bare.display(), "KKW §6.4 (course reserve)");
+        let back = serde_yaml_ng::to_string(&bare).unwrap();
+        assert_eq!(back.trim(), "KKW §6.4 (course reserve)");
+
+        // A mapping keeps its fields, and `ref` is the key's YAML spelling.
+        let mapped: Citation =
+            serde_yaml_ng::from_str("{ ref: kuriyan2012molecules, locator: \"§6.4\" }").unwrap();
+        assert_eq!(mapped.reference.as_deref(), Some("kuriyan2012molecules"));
+        assert_eq!(mapped.display(), "kuriyan2012molecules §6.4");
+        let back = serde_yaml_ng::to_string(&mapped).unwrap();
+        assert!(back.contains("ref: kuriyan2012molecules"));
+        assert!(back.contains("locator:"));
+    }
 }

src/model/taxonomy.rs

@@ -423,17 +423,53 @@ pub enum Format {
     MultipleResponse,
     /// Two options, True and False.
     TrueFalse,
+    /// A free-text answer the student writes rather than selects.
+    ///
+    /// It carries no options and is not machine-scored. What a grader marks it
+    /// against, and what a solutions document shows, lives in the item's
+    /// [`crate::item::Solution`]: a model answer and, when the item is worth more
+    /// than a point, a rubric. This is the format for "explain", "derive", and
+    /// "estimate" prompts that a set of distractors would trivialize.
+    OpenResponse,
 }
 
 impl Format {
+    /// Every response format.
+    pub const ALL: [Format; 4] = [
+        Format::SingleBestAnswer,
+        Format::MultipleResponse,
+        Format::TrueFalse,
+        Format::OpenResponse,
+    ];
+
     /// The QTI question type Canvas expects for this format.
     pub fn qti_type(self) -> &'static str {
         match self {
             Format::SingleBestAnswer => "multiple_choice_question",
             Format::MultipleResponse => "multiple_answers_question",
             Format::TrueFalse => "true_false_question",
+            Format::OpenResponse => "essay_question",
         }
     }
+
+    /// The snake_case token used in YAML.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Format::SingleBestAnswer => "single_best_answer",
+            Format::MultipleResponse => "multiple_response",
+            Format::TrueFalse => "true_false",
+            Format::OpenResponse => "open_response",
+        }
+    }
+
+    /// Whether items in this format present selectable options.
+    ///
+    /// `false` only for [`Format::OpenResponse`]. Validation, assembly, and the
+    /// exporters branch on this rather than on the variant, so the day a second
+    /// free-text format is added it inherits the no-options handling for free.
+    pub fn has_options(self) -> bool {
+        !matches!(self, Format::OpenResponse)
+    }
 }
 
 /// How strongly an item is expected to separate strong from weak students.
@@ -633,4 +669,18 @@ mod tests {
             Status::InReview
         );
     }
+
+    #[test]
+    fn open_response_is_the_only_format_without_options() {
+        assert_eq!(
+            serde_json::from_str::<Format>("\"open_response\"").unwrap(),
+            Format::OpenResponse
+        );
+        assert_eq!(Format::OpenResponse.as_str(), "open_response");
+        assert_eq!(Format::OpenResponse.qti_type(), "essay_question");
+        assert!(!Format::OpenResponse.has_options());
+        for f in Format::ALL {
+            assert_eq!(f.has_options(), f != Format::OpenResponse);
+        }
+    }
 }

src/util/markup.rs

@@ -113,6 +113,32 @@ pub fn to_plain(src: &str) -> String {
     out.trim().to_string()
 }
 
+/// Converts authoring markup to Pandoc-flavoured Markdown, for a Quarto document.
+///
+/// Subscripts and superscripts become Pandoc's `~x~` and `^x^`, the symbol table
+/// renders as Unicode, and the bold, italic, and inline-code spans are already
+/// Markdown, so they pass through unchanged. Paragraph breaks are kept. Nothing is
+/// HTML-escaped, because the consumer is a Markdown renderer rather than a page.
+///
+/// # Arguments
+///
+/// * `src` - the authoring source.
+///
+/// # Returns
+///
+/// Pandoc Markdown, trimmed, with paragraph breaks preserved.
+pub fn to_markdown(src: &str) -> String {
+    let symbolized = apply_symbols(src, false);
+    let mut out = wrap_bracket(&symbolized, "#sub[", "~", "~");
+    out = wrap_bracket(&out, "#sup[", "^", "^");
+    out.lines()
+        .map(|l| l.trim_end())
+        .collect::<Vec<_>>()
+        .join("\n")
+        .trim()
+        .to_string()
+}
+
 /// Passes authoring markup through for Typst.
 ///
 /// The markup is already a Typst subset, so this only normalizes whitespace and
@@ -379,4 +405,21 @@ mod tests {
         assert_eq!(to_typst("a @ b"), "a \\@ b");
         assert_eq!(to_typst("x < y"), "x \\< y");
     }
+
+    #[test]
+    fn markdown_uses_pandoc_scripts_and_unicode_symbols() {
+        assert_eq!(to_markdown("H#sub[2]O"), "H~2~O");
+        assert_eq!(to_markdown("x#sup[2]"), "x^2^");
+        assert_eq!(
+            to_markdown("K#sub[m] #sym.approx 5 mM"),
+            "K~m~ \u{2248} 5 mM"
+        );
+        // Bold, italic, and code are already Markdown.
+        assert_eq!(
+            to_markdown("**bold** and *em* and `code`"),
+            "**bold** and *em* and `code`"
+        );
+        // Paragraph breaks survive.
+        assert_eq!(to_markdown("one\n\ntwo"), "one\n\ntwo");
+    }
 }