Initial commit

brittle-core/src/bibtex/export.rs

@@ -0,0 +1,179 @@
+use crate::bibtex::validation::validate_for_export;
+use crate::error::BibtexError;
+use crate::model::{Person, Reference};
+
+/// Escape a BibTeX field value by wrapping special characters in braces.
+/// Handles `{`, `}`, `\`, and preserves existing braced groups.
+fn escape_field(value: &str) -> String {
+    // Wrap the whole value in braces — simple and safe for most content.
+    // This prevents BibTeX from case-folding titles and handles special chars.
+    format!("{{{value}}}")
+}
+
+/// Format a list of persons as a BibTeX "and"-separated author string.
+fn format_persons(persons: &[Person]) -> String {
+    persons
+        .iter()
+        .map(|p| p.to_bibtex())
+        .collect::<Vec<_>>()
+        .join(" and ")
+}
+
+/// Export a single reference as a BibTeX entry string.
+///
+/// Returns an error if required fields are missing.
+pub fn export_reference(reference: &Reference) -> Result<String, BibtexError> {
+    validate_for_export(reference)?;
+
+    let mut out = String::new();
+
+    out.push('@');
+    out.push_str(reference.entry_type.bibtex_name());
+    out.push('{');
+    out.push_str(&reference.cite_key);
+    out.push_str(",\n");
+
+    // Authors and editors come first for readability.
+    if !reference.authors.is_empty() {
+        let authors = format_persons(&reference.authors);
+        out.push_str(&format!("  author = {},\n", escape_field(&authors)));
+    }
+    if !reference.editors.is_empty() {
+        let editors = format_persons(&reference.editors);
+        out.push_str(&format!("  editor = {},\n", escape_field(&editors)));
+    }
+
+    // All other fields in sorted order (BTreeMap guarantees this).
+    for (key, value) in &reference.fields {
+        out.push_str(&format!("  {key} = {},\n", escape_field(value)));
+    }
+
+    out.push('}');
+
+    Ok(out)
+}
+
+/// Export multiple references as a `.bib` file string.
+///
+/// Skips references with missing required fields and collects all errors.
+/// Returns the BibTeX string and a list of any export errors.
+pub fn export_references(references: &[Reference]) -> (String, Vec<BibtexError>) {
+    let mut out = String::new();
+    let mut errors = Vec::new();
+
+    for reference in references {
+        match export_reference(reference) {
+            Ok(entry) => {
+                if !out.is_empty() {
+                    out.push('\n');
+                }
+                out.push_str(&entry);
+                out.push('\n');
+            }
+            Err(e) => errors.push(e),
+        }
+    }
+
+    (out, errors)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::model::{EntryType, Person, Reference};
+
+    fn make_article() -> Reference {
+        let mut r = Reference::new("turing1950", EntryType::Article);
+        r.authors.push(Person {
+            family: "Turing".into(),
+            given: Some("Alan M.".into()),
+            prefix: None,
+            suffix: None,
+        });
+        r.fields.insert(
+            "title".into(),
+            "Computing Machinery and Intelligence".into(),
+        );
+        r.fields.insert("journal".into(), "Mind".into());
+        r.fields.insert("year".into(), "1950".into());
+        r.fields.insert("volume".into(), "59".into());
+        r
+    }
+
+    #[test]
+    fn article_export() {
+        let r = make_article();
+        let bibtex = export_reference(&r).unwrap();
+        assert!(bibtex.starts_with("@article{turing1950,"));
+        assert!(bibtex.contains("author = {Turing, Alan M.}"));
+        assert!(bibtex.contains("title = {Computing Machinery and Intelligence}"));
+        assert!(bibtex.contains("journal = {Mind}"));
+        assert!(bibtex.contains("year = {1950}"));
+    }
+
+    #[test]
+    fn multi_author_formatting() {
+        let mut r = Reference::new("ab2024", EntryType::Article);
+        r.authors.push(Person {
+            family: "Doe".into(),
+            given: Some("Jane".into()),
+            prefix: None,
+            suffix: None,
+        });
+        r.authors.push(Person {
+            family: "Smith".into(),
+            given: Some("John".into()),
+            prefix: None,
+            suffix: None,
+        });
+        r.fields.insert("title".into(), "A Paper".into());
+        r.fields.insert("journal".into(), "Nature".into());
+        r.fields.insert("year".into(), "2024".into());
+
+        let bibtex = export_reference(&r).unwrap();
+        assert!(bibtex.contains("Doe, Jane and Smith, John"));
+    }
+
+    #[test]
+    fn missing_required_field_returns_error() {
+        let mut r = make_article();
+        r.fields.remove("journal");
+        assert!(export_reference(&r).is_err());
+    }
+
+    #[test]
+    fn book_with_editor() {
+        let mut r = Reference::new("knuth1986", EntryType::Book);
+        r.editors.push(Person::new("Knuth"));
+        r.fields.insert("title".into(), "The TeXbook".into());
+        r.fields.insert("publisher".into(), "Addison-Wesley".into());
+        r.fields.insert("year".into(), "1986".into());
+
+        let bibtex = export_reference(&r).unwrap();
+        assert!(bibtex.starts_with("@book{"));
+        assert!(bibtex.contains("editor = {Knuth}"));
+    }
+
+    #[test]
+    fn fields_appear_in_sorted_order() {
+        let r = make_article();
+        let bibtex = export_reference(&r).unwrap();
+        let journal_pos = bibtex.find("journal").unwrap();
+        let title_pos = bibtex.find("title").unwrap();
+        let year_pos = bibtex.find("year").unwrap();
+        // BTreeMap order: journal < title < volume < year (alphabetical)
+        assert!(journal_pos < title_pos);
+        assert!(title_pos < year_pos);
+    }
+
+    #[test]
+    fn export_references_collects_errors() {
+        let good = make_article();
+        let bad = Reference::new("incomplete", EntryType::Article);
+        // Missing author, title, journal, year
+
+        let (bibtex, errors) = export_references(&[good, bad]);
+        assert_eq!(errors.len(), 1);
+        assert!(bibtex.contains("@article{turing1950,"));
+    }
+}

brittle-core/src/bibtex/mod.rs

@@ -0,0 +1,5 @@
+pub mod export;
+pub mod validation;
+
+pub use export::{export_reference, export_references};
+pub use validation::validate_for_export;

brittle-core/src/bibtex/validation.rs

@@ -0,0 +1,104 @@
+use crate::error::BibtexError;
+use crate::model::{EntryType, Reference};
+
+/// Returns the required fields for a given BibTeX entry type.
+fn required_fields(entry_type: &EntryType) -> &'static [&'static str] {
+    match entry_type {
+        EntryType::Article => &["author", "title", "journal", "year"],
+        EntryType::Book => &["title", "publisher", "year"],
+        EntryType::Booklet => &["title"],
+        EntryType::InBook => &["title", "publisher", "year", "chapter"],
+        EntryType::InCollection => &["author", "title", "booktitle", "publisher", "year"],
+        EntryType::InProceedings => &["author", "title", "booktitle", "year"],
+        EntryType::Manual => &["title"],
+        EntryType::MastersThesis => &["author", "title", "school", "year"],
+        EntryType::Misc => &[],
+        EntryType::PhdThesis => &["author", "title", "school", "year"],
+        EntryType::Proceedings => &["title", "year"],
+        EntryType::TechReport => &["author", "title", "institution", "year"],
+        EntryType::Unpublished => &["author", "title", "note"],
+        EntryType::Online => &["title", "url"],
+    }
+}
+
+/// Validate that a reference has all required fields for BibTeX export.
+/// Returns an error describing the first missing required field found.
+pub fn validate_for_export(reference: &Reference) -> Result<(), BibtexError> {
+    let required = required_fields(&reference.entry_type);
+
+    for &field in required {
+        let present = match field {
+            "author" => !reference.authors.is_empty(),
+            "editor" => !reference.editors.is_empty(),
+            _ => reference.fields.contains_key(field),
+        };
+        if !present {
+            return Err(BibtexError::MissingRequiredField {
+                cite_key: reference.cite_key.clone(),
+                entry_type: reference.entry_type.bibtex_name().to_owned(),
+                field: field.to_owned(),
+            });
+        }
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::model::{EntryType, Person, Reference};
+
+    fn make_article() -> Reference {
+        let mut r = Reference::new("doe2024", EntryType::Article);
+        r.authors.push(Person::new("Doe"));
+        r.fields.insert("title".into(), "A Paper".into());
+        r.fields.insert("journal".into(), "Nature".into());
+        r.fields.insert("year".into(), "2024".into());
+        r
+    }
+
+    #[test]
+    fn valid_article_passes() {
+        let r = make_article();
+        assert!(validate_for_export(&r).is_ok());
+    }
+
+    #[test]
+    fn article_missing_author_fails() {
+        let mut r = make_article();
+        r.authors.clear();
+        let err = validate_for_export(&r).unwrap_err();
+        assert!(
+            matches!(err, BibtexError::MissingRequiredField { field, .. } if field == "author")
+        );
+    }
+
+    #[test]
+    fn article_missing_journal_fails() {
+        let mut r = make_article();
+        r.fields.remove("journal");
+        let err = validate_for_export(&r).unwrap_err();
+        assert!(
+            matches!(err, BibtexError::MissingRequiredField { field, .. } if field == "journal")
+        );
+    }
+
+    #[test]
+    fn misc_has_no_required_fields() {
+        let r = Reference::new("anon", EntryType::Misc);
+        assert!(validate_for_export(&r).is_ok());
+    }
+
+    #[test]
+    fn phd_thesis_requires_school() {
+        let mut r = Reference::new("smith2020", EntryType::PhdThesis);
+        r.authors.push(Person::new("Smith"));
+        r.fields.insert("title".into(), "A Thesis".into());
+        r.fields.insert("year".into(), "2020".into());
+        let err = validate_for_export(&r).unwrap_err();
+        assert!(
+            matches!(err, BibtexError::MissingRequiredField { field, .. } if field == "school")
+        );
+    }
+}

brittle-core/src/bin/seed.rs

@@ -0,0 +1,286 @@
+//! Creates an example Brittle repository with realistic academic references.
+//!
+//! For references that have freely available PDFs (arXiv preprints and open
+//! author copies), the script downloads the PDF and attaches it to the
+//! reference.  Downloads that fail are skipped with a warning so the seed
+//! always completes even without network access.
+//!
+//! Usage:
+//!   brittle-seed [PATH]
+//!
+//! PATH defaults to `~/brittle-example`.  The directory must not already
+//! contain a git repository.
+
+use std::io::Read;
+use std::path::PathBuf;
+
+use brittle_core::{Brittle, EntryType, FsStore, Person, ReferenceId};
+
+fn main() {
+    let path = match std::env::args().nth(1) {
+        Some(p) => PathBuf::from(p),
+        None => {
+            let home = std::env::var("HOME").expect("HOME not set");
+            PathBuf::from(home).join("brittle-example")
+        }
+    };
+
+    if path.join(".git").exists() {
+        eprintln!("error: {} already contains a git repository", path.display());
+        std::process::exit(1);
+    }
+
+    std::fs::create_dir_all(&path).expect("could not create directory");
+
+    println!("Creating repository at {} …", path.display());
+    let mut b = Brittle::create(&path).expect("create repository");
+
+    // ── Libraries ─────────────────────────────────────────────────────────────
+
+    let cs   = b.create_library("Computer Science", None).unwrap();
+    let ml   = b.create_library("Machine Learning", Some(cs.id)).unwrap();
+    let sys  = b.create_library("Systems", Some(cs.id)).unwrap();
+    let math = b.create_library("Mathematics", None).unwrap();
+    let pl   = b.create_library("Programming Languages", Some(cs.id)).unwrap();
+
+    // ── References ────────────────────────────────────────────────────────────
+
+    // -- Machine Learning --
+
+    let mut r = b.create_reference("lecun1998gradient", EntryType::Article).unwrap();
+    r.authors = vec![
+        person("LeCun", "Yann"),
+        person("Bottou", "Léon"),
+        person("Bengio", "Yoshua"),
+        person("Haffner", "Patrick"),
+    ];
+    r.fields.insert("title".into(), "Gradient-based learning applied to document recognition".into());
+    r.fields.insert("journal".into(), "Proceedings of the IEEE".into());
+    r.fields.insert("volume".into(), "86".into());
+    r.fields.insert("number".into(), "11".into());
+    r.fields.insert("pages".into(), "2278--2324".into());
+    r.fields.insert("year".into(), "1998".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(ml.id, id).unwrap();
+    attach_pdf(&mut b, id, "http://yann.lecun.com/exdb/publis/pdf/lecun-01a.pdf");
+
+    let mut r = b.create_reference("vaswani2017attention", EntryType::InProceedings).unwrap();
+    r.authors = vec![
+        person("Vaswani", "Ashish"),
+        person("Shazeer", "Noam"),
+        person("Parmar", "Niki"),
+        person("Uszkoreit", "Jakob"),
+        person("Jones", "Llion"),
+        person("Gomez", "Aidan N."),
+        person("Kaiser", "Łukasz"),
+        person("Polosukhin", "Illia"),
+    ];
+    r.fields.insert("title".into(), "Attention Is All You Need".into());
+    r.fields.insert("booktitle".into(), "Advances in Neural Information Processing Systems".into());
+    r.fields.insert("volume".into(), "30".into());
+    r.fields.insert("year".into(), "2017".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(ml.id, id).unwrap();
+    attach_pdf(&mut b, id, "https://arxiv.org/pdf/1706.03762");
+
+    let mut r = b.create_reference("goodfellow2016deep", EntryType::Book).unwrap();
+    r.authors = vec![
+        person("Goodfellow", "Ian"),
+        person("Bengio", "Yoshua"),
+        person("Courville", "Aaron"),
+    ];
+    r.fields.insert("title".into(), "Deep Learning".into());
+    r.fields.insert("publisher".into(), "MIT Press".into());
+    r.fields.insert("year".into(), "2016".into());
+    r.fields.insert("url".into(), "http://www.deeplearningbook.org".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(ml.id, id).unwrap();
+    // No freely available PDF for this book.
+
+    let mut r = b.create_reference("ho2020denoising", EntryType::InProceedings).unwrap();
+    r.authors = vec![
+        person("Ho", "Jonathan"),
+        person("Jain", "Ajay"),
+        person("Abbeel", "Pieter"),
+    ];
+    r.fields.insert("title".into(), "Denoising Diffusion Probabilistic Models".into());
+    r.fields.insert("booktitle".into(), "Advances in Neural Information Processing Systems".into());
+    r.fields.insert("volume".into(), "33".into());
+    r.fields.insert("pages".into(), "6840--6851".into());
+    r.fields.insert("year".into(), "2020".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(ml.id, id).unwrap();
+    attach_pdf(&mut b, id, "https://arxiv.org/pdf/2006.11239");
+
+    // -- Systems --
+
+    let mut r = b.create_reference("lamport1978time", EntryType::Article).unwrap();
+    r.authors = vec![person("Lamport", "Leslie")];
+    r.fields.insert("title".into(), "Time, Clocks, and the Ordering of Events in a Distributed System".into());
+    r.fields.insert("journal".into(), "Communications of the ACM".into());
+    r.fields.insert("volume".into(), "21".into());
+    r.fields.insert("number".into(), "7".into());
+    r.fields.insert("pages".into(), "558--565".into());
+    r.fields.insert("year".into(), "1978".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(sys.id, id).unwrap();
+    attach_pdf(&mut b, id, "https://lamport.azurewebsites.net/pubs/time-clocks.pdf");
+
+    let mut r = b.create_reference("rosenblum1992lfs", EntryType::Article).unwrap();
+    r.authors = vec![
+        person("Rosenblum", "Mendel"),
+        person("Ousterhout", "John K."),
+    ];
+    r.fields.insert("title".into(), "The Design and Implementation of a Log-Structured File System".into());
+    r.fields.insert("journal".into(), "ACM Transactions on Computer Systems".into());
+    r.fields.insert("volume".into(), "10".into());
+    r.fields.insert("number".into(), "1".into());
+    r.fields.insert("pages".into(), "26--52".into());
+    r.fields.insert("year".into(), "1992".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(sys.id, id).unwrap();
+    // Paywalled; no freely available PDF.
+
+    let mut r = b.create_reference("dean2004mapreduce", EntryType::InProceedings).unwrap();
+    r.authors = vec![
+        person("Dean", "Jeffrey"),
+        person("Ghemawat", "Sanjay"),
+    ];
+    r.fields.insert("title".into(), "MapReduce: Simplified Data Processing on Large Clusters".into());
+    r.fields.insert("booktitle".into(), "OSDI".into());
+    r.fields.insert("pages".into(), "137--150".into());
+    r.fields.insert("year".into(), "2004".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(sys.id, id).unwrap();
+    attach_pdf(&mut b, id, "https://static.googleusercontent.com/media/research.google.com/en//archive/mapreduce-osdi04.pdf");
+
+    // -- Programming Languages --
+
+    let mut r = b.create_reference("milner1978polymorphism", EntryType::Article).unwrap();
+    r.authors = vec![person("Milner", "Robin")];
+    r.fields.insert("title".into(), "A Theory of Type Polymorphism in Programming".into());
+    r.fields.insert("journal".into(), "Journal of Computer and System Sciences".into());
+    r.fields.insert("volume".into(), "17".into());
+    r.fields.insert("number".into(), "3".into());
+    r.fields.insert("pages".into(), "348--375".into());
+    r.fields.insert("year".into(), "1978".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(pl.id, id).unwrap();
+    // Paywalled; no freely available PDF.
+
+    let mut r = b.create_reference("matsakis2014rust", EntryType::InProceedings).unwrap();
+    r.authors = vec![
+        person("Matsakis", "Nicholas D."),
+        person("Klock", "Felix S."),
+    ];
+    r.fields.insert("title".into(), "The Rust Language".into());
+    r.fields.insert("booktitle".into(), "ACM SIGAda Annual Conference on High Integrity Language Technology".into());
+    r.fields.insert("pages".into(), "103--104".into());
+    r.fields.insert("year".into(), "2014".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(pl.id, id).unwrap();
+    // Paywalled; no freely available PDF.
+
+    // -- Mathematics --
+
+    let mut r = b.create_reference("turing1936computable", EntryType::Article).unwrap();
+    r.authors = vec![person("Turing", "Alan M.")];
+    r.fields.insert("title".into(), "On Computable Numbers, with an Application to the Entscheidungsproblem".into());
+    r.fields.insert("journal".into(), "Proceedings of the London Mathematical Society".into());
+    r.fields.insert("volume".into(), "42".into());
+    r.fields.insert("number".into(), "1".into());
+    r.fields.insert("pages".into(), "230--265".into());
+    r.fields.insert("year".into(), "1936".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(math.id, id).unwrap();
+    // No freely available PDF.
+
+    let mut r = b.create_reference("knuth1984texbook", EntryType::Book).unwrap();
+    r.authors = vec![person("Knuth", "Donald E.")];
+    r.fields.insert("title".into(), "The TeXbook".into());
+    r.fields.insert("publisher".into(), "Addison-Wesley".into());
+    r.fields.insert("year".into(), "1984".into());
+    r.fields.insert("series".into(), "Computers and Typesetting".into());
+    r.fields.insert("volume".into(), "A".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(math.id, id).unwrap();
+    // Copyrighted book; no freely available PDF.
+
+    // A reference in both ML and Mathematics (cross-library membership).
+    let mut r = b.create_reference("cybenko1989approximation", EntryType::Article).unwrap();
+    r.authors = vec![person("Cybenko", "George")];
+    r.fields.insert("title".into(), "Approximation by Superpositions of a Sigmoidal Function".into());
+    r.fields.insert("journal".into(), "Mathematics of Control, Signals, and Systems".into());
+    r.fields.insert("volume".into(), "2".into());
+    r.fields.insert("number".into(), "4".into());
+    r.fields.insert("pages".into(), "303--314".into());
+    r.fields.insert("year".into(), "1989".into());
+    let id = r.id;
+    b.update_reference(r).unwrap();
+    b.add_to_library(ml.id, id).unwrap();
+    b.add_to_library(math.id, id).unwrap();
+    // Paywalled; no freely available PDF.
+
+    println!();
+    println!("Done.");
+    println!();
+    println!("  Libraries : Computer Science (Machine Learning, Systems, Programming Languages), Mathematics");
+    println!("  References: 12 across all libraries");
+    println!();
+    println!("Open the repository in Brittle with:  :open {}", path.display());
+}
+
+// ── PDF download ──────────────────────────────────────────────────────────────
+
+/// Download the PDF at `url` and attach it to `id`.  Prints progress and
+/// skips silently on any error so the seed always completes.
+fn attach_pdf(b: &mut Brittle<FsStore>, id: ReferenceId, url: &str) {
+    let label = url.rsplit('/').next().unwrap_or(url);
+    print!("  ↓  {label} … ");
+    std::io::Write::flush(&mut std::io::stdout()).ok();
+
+    match download(url) {
+        Err(e) => println!("skipped ({e})"),
+        Ok(bytes) => {
+            let tmp = std::env::temp_dir().join(format!("{id}.pdf"));
+            if let Err(e) = std::fs::write(&tmp, &bytes) {
+                println!("skipped (write: {e})");
+                return;
+            }
+            match b.attach_pdf(id, &tmp) {
+                Ok(_) => println!("{} KB", bytes.len() / 1024),
+                Err(e) => println!("skipped (attach: {e})"),
+            }
+            let _ = std::fs::remove_file(&tmp);
+        }
+    }
+}
+
+fn download(url: &str) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
+    let resp = ureq::get(url).call()?;
+    let mut buf = Vec::new();
+    resp.into_reader().read_to_end(&mut buf)?;
+    Ok(buf)
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+fn person(family: &str, given: &str) -> Person {
+    Person {
+        family: family.into(),
+        given: Some(given.into()),
+        prefix: None,
+        suffix: None,
+    }
+}

brittle-core/src/error.rs

@@ -0,0 +1,104 @@
+use std::path::PathBuf;
+use thiserror::Error;
+
+/// Top-level error returned from all public Brittle API methods.
+#[derive(Debug, Error)]
+pub enum BrittleError {
+    #[error("{0}")]
+    Store(#[from] StoreError),
+
+    #[error("{0}")]
+    Validation(#[from] ValidationError),
+
+    #[error("{0}")]
+    BibTeX(#[from] BibtexError),
+}
+
+/// Errors from the storage layer.
+#[derive(Debug, Error)]
+pub enum StoreError {
+    #[error("{entity_type} not found: {id}")]
+    NotFound { entity_type: EntityType, id: String },
+
+    #[error("I/O error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("serialization error: {message}")]
+    Serialization { message: String },
+
+    #[error("deserialization error for {path}: {message}")]
+    Deserialization { path: PathBuf, message: String },
+
+    #[error("git error: {0}")]
+    Git(#[from] git2::Error),
+
+    #[error("repository not found at {path}")]
+    RepoNotFound { path: PathBuf },
+
+    #[error("repository already exists at {path}")]
+    RepoAlreadyExists { path: PathBuf },
+}
+
+/// The kind of entity involved in a not-found error.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EntityType {
+    Reference,
+    Library,
+    Annotation,
+    Snapshot,
+}
+
+impl std::fmt::Display for EntityType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            EntityType::Reference => write!(f, "Reference"),
+            EntityType::Library => write!(f, "Library"),
+            EntityType::Annotation => write!(f, "Annotation"),
+            EntityType::Snapshot => write!(f, "Snapshot"),
+        }
+    }
+}
+
+/// Business logic validation errors.
+#[derive(Debug, Error)]
+pub enum ValidationError {
+    #[error(
+        "library cycle detected: moving library {library_id} under {parent_id} would create a cycle"
+    )]
+    LibraryCycle {
+        library_id: String,
+        parent_id: String,
+    },
+
+    #[error("library {id} has children and cannot be deleted; delete or move children first")]
+    LibraryHasChildren { id: String },
+
+    #[error("cite key already exists: {cite_key}")]
+    DuplicateCiteKey { cite_key: String },
+
+    #[error("cite key cannot be empty")]
+    EmptyCiteKey,
+
+    #[error("library name cannot be empty")]
+    EmptyLibraryName,
+
+    #[error("reference {reference_id} has no PDF attached")]
+    NoPdfAttached { reference_id: String },
+
+    #[error("PDF file not found: {path}")]
+    PdfNotFound { path: PathBuf },
+
+    #[error("there are uncommitted changes; create a snapshot or call discard_changes() first")]
+    UncommittedChanges,
+}
+
+/// Errors specific to BibTeX export.
+#[derive(Debug, Error)]
+pub enum BibtexError {
+    #[error("reference '{cite_key}' ({entry_type}): missing required field '{field}'")]
+    MissingRequiredField {
+        cite_key: String,
+        entry_type: String,
+        field: String,
+    },
+}

brittle-core/src/model/annotation.rs

@@ -0,0 +1,229 @@
+use crate::model::ids::{AnnotationId, ReferenceId};
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+
+/// A point in PDF coordinate space.
+/// Origin is bottom-left; units are points (1/72 inch), matching ISO 32000.
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub struct Point {
+    pub x: f64,
+    pub y: f64,
+}
+
+/// A rectangle in PDF coordinate space.
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub struct Rect {
+    pub x: f64,
+    pub y: f64,
+    pub width: f64,
+    pub height: f64,
+}
+
+/// A quadrilateral for text markup annotations (highlight, underline, etc.).
+/// Four points define one region, typically one line of text.
+/// Matches the PDF spec QuadPoints representation (4 vertices per quad).
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub struct Quad {
+    pub points: [Point; 4],
+}
+
+/// RGBA color.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Color {
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+    pub a: u8,
+}
+
+impl Color {
+    pub const YELLOW: Color = Color {
+        r: 255,
+        g: 255,
+        b: 0,
+        a: 128,
+    };
+    pub const RED: Color = Color {
+        r: 255,
+        g: 0,
+        b: 0,
+        a: 128,
+    };
+    pub const GREEN: Color = Color {
+        r: 0,
+        g: 255,
+        b: 0,
+        a: 128,
+    };
+}
+
+/// The four text markup annotation types defined in ISO 32000.
+/// All share the same QuadPoints-based geometry.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum TextMarkupType {
+    Highlight,
+    Underline,
+    Squiggly,
+    StrikeOut,
+}
+
+/// The kind of annotation and its type-specific geometry/data.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "lowercase")]
+pub enum AnnotationType {
+    /// Text markup (highlight, underline, squiggly, strikeout).
+    /// Uses QuadPoints per PDF spec for precise multi-line region selection.
+    TextMarkup {
+        markup_type: TextMarkupType,
+        quads: Vec<Quad>,
+        color: Color,
+        /// The selected text, stored for search and export without re-reading the PDF.
+        selected_text: Option<String>,
+    },
+    /// Sticky note (popup comment).
+    Note { position: Point },
+    /// Inline text box.
+    FreeText { rect: Rect },
+    /// Freehand ink drawing (e.g., circling a diagram).
+    Ink {
+        /// Multiple strokes, each a sequence of connected points.
+        paths: Vec<Vec<Point>>,
+        color: Color,
+        /// Stroke width in points.
+        width: f64,
+    },
+    /// Area/image selection for extracting figures from PDFs.
+    Area { rect: Rect },
+}
+
+/// A single annotation on a PDF page.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct Annotation {
+    pub id: AnnotationId,
+    pub reference_id: ReferenceId,
+    /// 0-indexed physical page number.
+    pub page: u32,
+    /// Display page label (e.g., "iv", "23") — may differ from the physical page index.
+    pub page_label: Option<String>,
+    pub annotation_type: AnnotationType,
+    /// Free-form text: note body, comment on a highlight, etc.
+    pub content: Option<String>,
+    pub created_at: DateTime<Utc>,
+    pub modified_at: DateTime<Utc>,
+}
+
+impl Annotation {
+    pub fn new(reference_id: ReferenceId, page: u32, annotation_type: AnnotationType) -> Self {
+        let now = Utc::now();
+        Self {
+            id: AnnotationId::new(),
+            reference_id,
+            page,
+            page_label: None,
+            annotation_type,
+            content: None,
+            created_at: now,
+            modified_at: now,
+        }
+    }
+}
+
+/// All annotations for a single reference, stored as one file.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct AnnotationSet {
+    pub reference_id: ReferenceId,
+    pub annotations: Vec<Annotation>,
+}
+
+impl AnnotationSet {
+    pub fn new(reference_id: ReferenceId) -> Self {
+        Self {
+            reference_id,
+            annotations: Vec::new(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn make_highlight() -> AnnotationType {
+        AnnotationType::TextMarkup {
+            markup_type: TextMarkupType::Highlight,
+            quads: vec![Quad {
+                points: [
+                    Point { x: 10.0, y: 20.0 },
+                    Point { x: 100.0, y: 20.0 },
+                    Point { x: 10.0, y: 30.0 },
+                    Point { x: 100.0, y: 30.0 },
+                ],
+            }],
+            color: Color::YELLOW,
+            selected_text: Some("important text".into()),
+        }
+    }
+
+    #[test]
+    fn annotation_serde_round_trip_highlight() {
+        let ref_id = ReferenceId::new();
+        let set = AnnotationSet {
+            reference_id: ref_id,
+            annotations: vec![Annotation::new(ref_id, 3, make_highlight())],
+        };
+
+        let toml_str = toml::to_string(&set).expect("serialize");
+        let set2: AnnotationSet = toml::from_str(&toml_str).expect("deserialize");
+
+        assert_eq!(set.reference_id, set2.reference_id);
+        assert_eq!(set.annotations.len(), set2.annotations.len());
+        assert_eq!(set.annotations[0].page, set2.annotations[0].page);
+    }
+
+    #[test]
+    fn annotation_serde_round_trip_ink() {
+        let ref_id = ReferenceId::new();
+        let ink = AnnotationType::Ink {
+            paths: vec![vec![Point { x: 0.0, y: 0.0 }, Point { x: 10.0, y: 10.0 }]],
+            color: Color::RED,
+            width: 2.0,
+        };
+        let set = AnnotationSet {
+            reference_id: ref_id,
+            annotations: vec![Annotation::new(ref_id, 0, ink)],
+        };
+
+        let toml_str = toml::to_string(&set).expect("serialize");
+        let set2: AnnotationSet = toml::from_str(&toml_str).expect("deserialize");
+        assert_eq!(set, set2);
+    }
+
+    #[test]
+    fn all_markup_types_serialize() {
+        let ref_id = ReferenceId::new();
+        for markup_type in [
+            TextMarkupType::Highlight,
+            TextMarkupType::Underline,
+            TextMarkupType::Squiggly,
+            TextMarkupType::StrikeOut,
+        ] {
+            let ann = Annotation::new(
+                ref_id,
+                0,
+                AnnotationType::TextMarkup {
+                    markup_type,
+                    quads: vec![],
+                    color: Color::GREEN,
+                    selected_text: None,
+                },
+            );
+            let set = AnnotationSet {
+                reference_id: ref_id,
+                annotations: vec![ann],
+            };
+            let toml_str = toml::to_string(&set).expect("serialize");
+            let _: AnnotationSet = toml::from_str(&toml_str).expect("deserialize");
+        }
+    }
+}

brittle-core/src/model/ids.rs

@@ -0,0 +1,67 @@
+use serde::{Deserialize, Serialize};
+use std::fmt;
+use uuid::Uuid;
+
+macro_rules! define_id {
+    ($name:ident) => {
+        #[derive(
+            Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize,
+        )]
+        pub struct $name(pub Uuid);
+
+        impl $name {
+            pub fn new() -> Self {
+                Self(Uuid::now_v7())
+            }
+        }
+
+        impl Default for $name {
+            fn default() -> Self {
+                Self::new()
+            }
+        }
+
+        impl From<Uuid> for $name {
+            fn from(uuid: Uuid) -> Self {
+                Self(uuid)
+            }
+        }
+
+        impl fmt::Display for $name {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                write!(f, "{}", self.0)
+            }
+        }
+    };
+}
+
+define_id!(ReferenceId);
+define_id!(LibraryId);
+define_id!(AnnotationId);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_generates_unique_ids() {
+        let a = ReferenceId::new();
+        let b = ReferenceId::new();
+        assert_ne!(a, b);
+    }
+
+    #[test]
+    fn display_is_uuid_format() {
+        let id = ReferenceId::new();
+        let s = id.to_string();
+        assert_eq!(s.len(), 36); // UUID hyphenated format
+    }
+
+    #[test]
+    fn serde_round_trip() {
+        let id = LibraryId::new();
+        let json = serde_json::to_string(&id).unwrap();
+        let id2: LibraryId = serde_json::from_str(&json).unwrap();
+        assert_eq!(id, id2);
+    }
+}

brittle-core/src/model/library.rs

@@ -0,0 +1,66 @@
+use crate::model::ids::{LibraryId, ReferenceId};
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeSet;
+
+/// A named collection of references. Forms a tree via `parent_id`.
+///
+/// References are not "owned" by a library — they exist in a flat pool.
+/// A reference can appear in multiple libraries (multi-membership).
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Library {
+    pub id: LibraryId,
+    pub name: String,
+    /// `None` means this is a root library (no parent).
+    pub parent_id: Option<LibraryId>,
+    /// The set of references that are members of this library.
+    /// BTreeSet for deterministic serialization order.
+    pub members: BTreeSet<ReferenceId>,
+    pub created_at: DateTime<Utc>,
+    pub modified_at: DateTime<Utc>,
+}
+
+impl Library {
+    pub fn new(name: impl Into<String>, parent_id: Option<LibraryId>) -> Self {
+        let now = Utc::now();
+        Self {
+            id: LibraryId::new(),
+            name: name.into(),
+            parent_id,
+            members: BTreeSet::new(),
+            created_at: now,
+            modified_at: now,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn library_serde_round_trip() {
+        let mut lib = Library::new("Machine Learning", None);
+        let ref_id = ReferenceId::new();
+        lib.members.insert(ref_id);
+
+        let toml_str = toml::to_string(&lib).expect("serialize to TOML");
+        let lib2: Library = toml::from_str(&toml_str).expect("deserialize from TOML");
+
+        assert_eq!(lib.id, lib2.id);
+        assert_eq!(lib.name, lib2.name);
+        assert_eq!(lib.members, lib2.members);
+        assert_eq!(lib.parent_id, lib2.parent_id);
+    }
+
+    #[test]
+    fn nested_library_serde_round_trip() {
+        let parent = Library::new("Science", None);
+        let child = Library::new("Physics", Some(parent.id));
+
+        let toml_str = toml::to_string(&child).expect("serialize to TOML");
+        let child2: Library = toml::from_str(&toml_str).expect("deserialize from TOML");
+
+        assert_eq!(child2.parent_id, Some(parent.id));
+    }
+}

brittle-core/src/model/mod.rs

@@ -0,0 +1,13 @@
+pub mod annotation;
+pub mod ids;
+pub mod library;
+pub mod reference;
+pub mod snapshot;
+
+pub use annotation::{
+    Annotation, AnnotationSet, AnnotationType, Color, Point, Quad, Rect, TextMarkupType,
+};
+pub use ids::{AnnotationId, LibraryId, ReferenceId};
+pub use library::Library;
+pub use reference::{EntryType, PdfAttachment, Person, Reference};
+pub use snapshot::Snapshot;

brittle-core/src/model/reference.rs

@@ -0,0 +1,241 @@
+use crate::model::ids::ReferenceId;
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+use std::fmt;
+use std::path::PathBuf;
+
+/// A person (author, editor, translator, etc.).
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Person {
+    pub family: String,
+    pub given: Option<String>,
+    /// Name prefix: "von", "de", "van der", etc.
+    pub prefix: Option<String>,
+    /// Name suffix: "Jr.", "III", etc.
+    pub suffix: Option<String>,
+}
+
+impl Person {
+    pub fn new(family: impl Into<String>) -> Self {
+        Self {
+            family: family.into(),
+            given: None,
+            prefix: None,
+            suffix: None,
+        }
+    }
+
+    /// Format for display: "Given prefix Family, Suffix" — natural reading order.
+    pub fn display_name(&self) -> String {
+        let mut parts = Vec::new();
+        if let Some(given) = &self.given {
+            parts.push(given.as_str());
+        }
+        if let Some(prefix) = &self.prefix {
+            parts.push(prefix.as_str());
+        }
+        parts.push(self.family.as_str());
+        let mut name = parts.join(" ");
+        if let Some(suffix) = &self.suffix {
+            name.push_str(", ");
+            name.push_str(suffix);
+        }
+        name
+    }
+
+    /// Format as BibTeX expects: "{prefix} {family}, {suffix}, {given}".
+    /// Falls back gracefully when optional parts are absent.
+    pub fn to_bibtex(&self) -> String {
+        let mut family_part = String::new();
+        if let Some(prefix) = &self.prefix {
+            family_part.push_str(prefix);
+            family_part.push(' ');
+        }
+        family_part.push_str(&self.family);
+
+        match (&self.suffix, &self.given) {
+            (Some(suffix), Some(given)) => {
+                format!("{family_part}, {suffix}, {given}")
+            }
+            (Some(suffix), None) => format!("{family_part}, {suffix}"),
+            (None, Some(given)) => format!("{family_part}, {given}"),
+            (None, None) => family_part,
+        }
+    }
+}
+
+impl fmt::Display for Person {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.display_name())
+    }
+}
+
+/// Standard BibTeX and common BibLaTeX entry types.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum EntryType {
+    Article,
+    Book,
+    Booklet,
+    InBook,
+    InCollection,
+    InProceedings,
+    Manual,
+    MastersThesis,
+    Misc,
+    PhdThesis,
+    Proceedings,
+    TechReport,
+    Unpublished,
+    Online,
+}
+
+impl EntryType {
+    /// The BibTeX entry type name as it appears in `.bib` files.
+    pub fn bibtex_name(&self) -> &'static str {
+        match self {
+            EntryType::Article => "article",
+            EntryType::Book => "book",
+            EntryType::Booklet => "booklet",
+            EntryType::InBook => "inbook",
+            EntryType::InCollection => "incollection",
+            EntryType::InProceedings => "inproceedings",
+            EntryType::Manual => "manual",
+            EntryType::MastersThesis => "mastersthesis",
+            EntryType::Misc => "misc",
+            EntryType::PhdThesis => "phdthesis",
+            EntryType::Proceedings => "proceedings",
+            EntryType::TechReport => "techreport",
+            EntryType::Unpublished => "unpublished",
+            EntryType::Online => "online",
+        }
+    }
+}
+
+/// A PDF file stored inside the Brittle repository.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PdfAttachment {
+    /// Path relative to the repository root (e.g., `"pdfs/550e8400-....pdf"`).
+    pub stored_path: PathBuf,
+    /// SHA-256 hex digest of the file contents for integrity verification.
+    pub content_hash: String,
+}
+
+/// A citable work. The core entity of Brittle.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct Reference {
+    pub id: ReferenceId,
+    /// The BibTeX cite key (e.g., `"knuth1984texbook"`). User-facing and mutable.
+    pub cite_key: String,
+    pub entry_type: EntryType,
+    /// Authors listed in order.
+    pub authors: Vec<Person>,
+    /// Editors (for edited books, proceedings, etc.).
+    pub editors: Vec<Person>,
+    /// All other fields (title, year, journal, volume, etc.) as plain strings.
+    /// BTreeMap for deterministic serialization order (important for git diffs).
+    pub fields: BTreeMap<String, String>,
+    pub pdf: Option<PdfAttachment>,
+    pub created_at: DateTime<Utc>,
+    pub modified_at: DateTime<Utc>,
+}
+
+impl Reference {
+    pub fn new(cite_key: impl Into<String>, entry_type: EntryType) -> Self {
+        let now = Utc::now();
+        Self {
+            id: ReferenceId::new(),
+            cite_key: cite_key.into(),
+            entry_type,
+            authors: Vec::new(),
+            editors: Vec::new(),
+            fields: BTreeMap::new(),
+            pdf: None,
+            created_at: now,
+            modified_at: now,
+        }
+    }
+
+    /// Returns the value of the `title` field, if present.
+    pub fn title(&self) -> Option<&str> {
+        self.fields.get("title").map(String::as_str)
+    }
+
+    /// Returns the value of the `year` field, if present.
+    pub fn year(&self) -> Option<&str> {
+        self.fields.get("year").map(String::as_str)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn person_bibtex_full() {
+        let p = Person {
+            family: "Dijkstra".into(),
+            given: Some("Edsger W.".into()),
+            prefix: None,
+            suffix: None,
+        };
+        assert_eq!(p.to_bibtex(), "Dijkstra, Edsger W.");
+    }
+
+    #[test]
+    fn person_bibtex_with_prefix() {
+        let p = Person {
+            family: "Beethoven".into(),
+            given: Some("Ludwig".into()),
+            prefix: Some("van".into()),
+            suffix: None,
+        };
+        assert_eq!(p.to_bibtex(), "van Beethoven, Ludwig");
+    }
+
+    #[test]
+    fn person_bibtex_with_suffix() {
+        let p = Person {
+            family: "King".into(),
+            given: Some("Martin Luther".into()),
+            prefix: None,
+            suffix: Some("Jr.".into()),
+        };
+        assert_eq!(p.to_bibtex(), "King, Jr., Martin Luther");
+    }
+
+    #[test]
+    fn person_bibtex_family_only() {
+        let p = Person::new("Aristotle");
+        assert_eq!(p.to_bibtex(), "Aristotle");
+    }
+
+    #[test]
+    fn reference_serde_round_trip() {
+        let mut r = Reference::new("doe2024", EntryType::Article);
+        r.authors.push(Person {
+            family: "Doe".into(),
+            given: Some("Jane".into()),
+            prefix: None,
+            suffix: None,
+        });
+        r.fields.insert("title".into(), "A Great Paper".into());
+        r.fields.insert("year".into(), "2024".into());
+
+        let toml_str = toml::to_string(&r).expect("serialize to TOML");
+        let r2: Reference = toml::from_str(&toml_str).expect("deserialize from TOML");
+
+        assert_eq!(r.id, r2.id);
+        assert_eq!(r.cite_key, r2.cite_key);
+        assert_eq!(r.authors, r2.authors);
+        assert_eq!(r.fields, r2.fields);
+    }
+
+    #[test]
+    fn entry_type_bibtex_names() {
+        assert_eq!(EntryType::Article.bibtex_name(), "article");
+        assert_eq!(EntryType::InProceedings.bibtex_name(), "inproceedings");
+        assert_eq!(EntryType::PhdThesis.bibtex_name(), "phdthesis");
+    }
+}

brittle-core/src/model/snapshot.rs

@@ -0,0 +1,12 @@
+use chrono::{DateTime, Utc};
+use serde::Serialize;
+
+/// Metadata about a stored snapshot (git commit).
+/// Not serialized to files — read directly from git history.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
+pub struct Snapshot {
+    /// Git commit SHA (hex string).
+    pub id: String,
+    pub message: String,
+    pub timestamp: DateTime<Utc>,
+}

brittle-core/src/store/fs.rs

@@ -0,0 +1,448 @@
+use crate::error::{EntityType, StoreError};
+use crate::model::{AnnotationSet, Library, LibraryId, Reference, ReferenceId, Snapshot};
+use crate::store::Store;
+use chrono::{DateTime, TimeZone, Utc};
+use git2::{IndexAddOption, Repository, Signature};
+use std::path::{Path, PathBuf};
+
+const REFERENCES_DIR: &str = "references";
+const LIBRARIES_DIR: &str = "libraries";
+const ANNOTATIONS_DIR: &str = "annotations";
+const PDFS_DIR: &str = "pdfs";
+
+/// Filesystem + git-backed store. Each entity is a TOML file.
+/// Snapshots are git commits; time travel is git checkout.
+pub struct FsStore {
+    root: PathBuf,
+    repo: Repository,
+}
+
+impl FsStore {
+    /// Create a new Brittle repository at the given path.
+    /// Fails if the path already contains a git repository.
+    pub fn create(path: &Path) -> Result<Self, StoreError> {
+        if path.join(".git").exists() {
+            return Err(StoreError::RepoAlreadyExists {
+                path: path.to_owned(),
+            });
+        }
+
+        let repo = Repository::init(path).map_err(StoreError::Git)?;
+
+        // Create subdirectories.
+        for dir in [REFERENCES_DIR, LIBRARIES_DIR, ANNOTATIONS_DIR, PDFS_DIR] {
+            std::fs::create_dir_all(path.join(dir))?;
+        }
+
+        let mut store = Self {
+            root: path.to_owned(),
+            repo,
+        };
+
+        // Create the initial commit so the repo has a HEAD.
+        store.commit_all("Initialize Brittle repository")?;
+
+        Ok(store)
+    }
+
+    /// Open an existing Brittle repository.
+    pub fn open(path: &Path) -> Result<Self, StoreError> {
+        let repo = Repository::open(path).map_err(|_| StoreError::RepoNotFound {
+            path: path.to_owned(),
+        })?;
+        Ok(Self {
+            root: path.to_owned(),
+            repo,
+        })
+    }
+
+    /// Stage all changes and create a git commit. Returns the commit OID as hex.
+    fn commit_all(&mut self, message: &str) -> Result<String, StoreError> {
+        let mut index = self.repo.index().map_err(StoreError::Git)?;
+        index
+            .add_all(["*"].iter(), IndexAddOption::DEFAULT, None)
+            .map_err(StoreError::Git)?;
+        index.write().map_err(StoreError::Git)?;
+
+        let tree_oid = index.write_tree().map_err(StoreError::Git)?;
+        let tree = self.repo.find_tree(tree_oid).map_err(StoreError::Git)?;
+
+        let sig = Signature::now("Brittle", "brittle@local").map_err(StoreError::Git)?;
+
+        let parent_commit = self.repo.head().ok().and_then(|h| h.peel_to_commit().ok());
+
+        let oid = match &parent_commit {
+            Some(parent) => self
+                .repo
+                .commit(Some("HEAD"), &sig, &sig, message, &tree, &[parent])
+                .map_err(StoreError::Git)?,
+            None => self
+                .repo
+                .commit(Some("HEAD"), &sig, &sig, message, &tree, &[])
+                .map_err(StoreError::Git)?,
+        };
+
+        Ok(oid.to_string())
+    }
+
+    fn reference_path(&self, id: ReferenceId) -> PathBuf {
+        self.root.join(REFERENCES_DIR).join(format!("{id}.toml"))
+    }
+
+    fn library_path(&self, id: LibraryId) -> PathBuf {
+        self.root.join(LIBRARIES_DIR).join(format!("{id}.toml"))
+    }
+
+    fn annotation_path(&self, ref_id: ReferenceId) -> PathBuf {
+        self.root
+            .join(ANNOTATIONS_DIR)
+            .join(format!("{ref_id}.toml"))
+    }
+
+    pub fn pdf_dir(&self) -> PathBuf {
+        self.root.join(PDFS_DIR)
+    }
+
+    /// Returns the repository root directory.
+    pub fn root(&self) -> &Path {
+        &self.root
+    }
+
+    fn write_toml<T: serde::Serialize>(&self, path: &Path, value: &T) -> Result<(), StoreError> {
+        let content = toml::to_string(value).map_err(|e| StoreError::Serialization {
+            message: e.to_string(),
+        })?;
+        std::fs::write(path, content)?;
+        Ok(())
+    }
+
+    fn read_toml<T: serde::de::DeserializeOwned>(&self, path: &Path) -> Result<T, StoreError> {
+        let content = std::fs::read_to_string(path)?;
+        toml::from_str(&content).map_err(|e| StoreError::Deserialization {
+            path: path.to_owned(),
+            message: e.to_string(),
+        })
+    }
+
+    fn ids_from_dir<T, F>(&self, dir: &str, parse: F) -> Result<Vec<T>, StoreError>
+    where
+        F: Fn(&str) -> Option<T>,
+    {
+        let dir_path = self.root.join(dir);
+        let mut ids = Vec::new();
+        for entry in std::fs::read_dir(&dir_path)? {
+            let entry = entry?;
+            let name = entry.file_name();
+            let name = name.to_string_lossy();
+            if let Some(stem) = name.strip_suffix(".toml")
+                && let Some(id) = parse(stem)
+            {
+                ids.push(id);
+            }
+        }
+        Ok(ids)
+    }
+}
+
+impl Store for FsStore {
+    fn save_reference(&mut self, reference: &Reference) -> Result<(), StoreError> {
+        self.write_toml(&self.reference_path(reference.id), reference)
+    }
+
+    fn load_reference(&self, id: ReferenceId) -> Result<Reference, StoreError> {
+        let path = self.reference_path(id);
+        if !path.exists() {
+            return Err(StoreError::NotFound {
+                entity_type: EntityType::Reference,
+                id: id.to_string(),
+            });
+        }
+        self.read_toml(&path)
+    }
+
+    fn delete_reference(&mut self, id: ReferenceId) -> Result<(), StoreError> {
+        let path = self.reference_path(id);
+        if !path.exists() {
+            return Err(StoreError::NotFound {
+                entity_type: EntityType::Reference,
+                id: id.to_string(),
+            });
+        }
+        std::fs::remove_file(path)?;
+        Ok(())
+    }
+
+    fn list_reference_ids(&self) -> Result<Vec<ReferenceId>, StoreError> {
+        self.ids_from_dir(REFERENCES_DIR, |s| {
+            s.parse::<uuid::Uuid>().ok().map(ReferenceId::from)
+        })
+    }
+
+    fn save_library(&mut self, library: &Library) -> Result<(), StoreError> {
+        self.write_toml(&self.library_path(library.id), library)
+    }
+
+    fn load_library(&self, id: LibraryId) -> Result<Library, StoreError> {
+        let path = self.library_path(id);
+        if !path.exists() {
+            return Err(StoreError::NotFound {
+                entity_type: EntityType::Library,
+                id: id.to_string(),
+            });
+        }
+        self.read_toml(&path)
+    }
+
+    fn delete_library(&mut self, id: LibraryId) -> Result<(), StoreError> {
+        let path = self.library_path(id);
+        if !path.exists() {
+            return Err(StoreError::NotFound {
+                entity_type: EntityType::Library,
+                id: id.to_string(),
+            });
+        }
+        std::fs::remove_file(path)?;
+        Ok(())
+    }
+
+    fn list_library_ids(&self) -> Result<Vec<LibraryId>, StoreError> {
+        self.ids_from_dir(LIBRARIES_DIR, |s| {
+            s.parse::<uuid::Uuid>().ok().map(LibraryId::from)
+        })
+    }
+
+    fn load_annotations(&self, ref_id: ReferenceId) -> Result<AnnotationSet, StoreError> {
+        let path = self.annotation_path(ref_id);
+        if !path.exists() {
+            return Ok(AnnotationSet::new(ref_id));
+        }
+        self.read_toml(&path)
+    }
+
+    fn save_annotations(&mut self, set: &AnnotationSet) -> Result<(), StoreError> {
+        self.write_toml(&self.annotation_path(set.reference_id), set)
+    }
+
+    fn delete_annotations(&mut self, ref_id: ReferenceId) -> Result<(), StoreError> {
+        let path = self.annotation_path(ref_id);
+        if path.exists() {
+            std::fs::remove_file(path)?;
+        }
+        Ok(())
+    }
+
+    fn create_snapshot(&mut self, message: &str) -> Result<Snapshot, StoreError> {
+        let oid = self.commit_all(message)?;
+        let commit = self
+            .repo
+            .find_commit(git2::Oid::from_str(&oid).map_err(StoreError::Git)?)
+            .map_err(StoreError::Git)?;
+        let timestamp = commit_timestamp(&commit)?;
+
+        Ok(Snapshot {
+            id: oid,
+            message: message.to_owned(),
+            timestamp,
+        })
+    }
+
+    fn list_snapshots(&self) -> Result<Vec<Snapshot>, StoreError> {
+        let mut revwalk = self.repo.revwalk().map_err(StoreError::Git)?;
+        revwalk.push_head().map_err(StoreError::Git)?;
+        revwalk
+            .set_sorting(git2::Sort::TIME)
+            .map_err(StoreError::Git)?;
+
+        let mut snapshots = Vec::new();
+        for oid in revwalk {
+            let oid = oid.map_err(StoreError::Git)?;
+            let commit = self.repo.find_commit(oid).map_err(StoreError::Git)?;
+            let message = commit.message().unwrap_or("").to_owned();
+            let timestamp = commit_timestamp(&commit)?;
+            snapshots.push(Snapshot {
+                id: oid.to_string(),
+                message,
+                timestamp,
+            });
+        }
+
+        Ok(snapshots)
+    }
+
+    fn restore_snapshot(&mut self, snapshot_id: &str) -> Result<(), StoreError> {
+        let oid = git2::Oid::from_str(snapshot_id).map_err(|_| StoreError::NotFound {
+            entity_type: EntityType::Snapshot,
+            id: snapshot_id.to_owned(),
+        })?;
+
+        let commit = self
+            .repo
+            .find_commit(oid)
+            .map_err(|_| StoreError::NotFound {
+                entity_type: EntityType::Snapshot,
+                id: snapshot_id.to_owned(),
+            })?;
+
+        let tree = commit.tree().map_err(StoreError::Git)?;
+
+        // Checkout the tree, updating both the index and the working directory.
+        // `force` overwrites modified tracked files; `remove_untracked` removes
+        // files that were written since the last snapshot but never committed.
+        let mut checkout_opts = git2::build::CheckoutBuilder::new();
+        checkout_opts.force().remove_untracked(true);
+        self.repo
+            .checkout_tree(tree.as_object(), Some(&mut checkout_opts))
+            .map_err(StoreError::Git)?;
+
+        // Move HEAD to point at the restored commit.
+        self.repo.set_head_detached(oid).map_err(StoreError::Git)?;
+
+        Ok(())
+    }
+
+    fn has_uncommitted_changes(&self) -> Result<bool, StoreError> {
+        let statuses = self
+            .repo
+            .statuses(Some(
+                git2::StatusOptions::new()
+                    .include_untracked(true)
+                    .recurse_untracked_dirs(true),
+            ))
+            .map_err(StoreError::Git)?;
+        Ok(!statuses.is_empty())
+    }
+}
+
+fn commit_timestamp(commit: &git2::Commit<'_>) -> Result<DateTime<Utc>, StoreError> {
+    let time = commit.time();
+    Utc.timestamp_opt(time.seconds(), 0)
+        .single()
+        .ok_or_else(|| StoreError::Serialization {
+            message: "invalid commit timestamp".into(),
+        })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::model::{EntryType, Library, Reference};
+
+    fn make_store(dir: &Path) -> FsStore {
+        FsStore::create(dir).expect("create store")
+    }
+
+    #[test]
+    fn create_and_open() {
+        let tmp = tempfile::tempdir().unwrap();
+        let store = make_store(tmp.path());
+        drop(store);
+        FsStore::open(tmp.path()).expect("re-open store");
+    }
+
+    #[test]
+    fn create_fails_if_repo_exists() {
+        let tmp = tempfile::tempdir().unwrap();
+        make_store(tmp.path());
+        assert!(FsStore::create(tmp.path()).is_err());
+    }
+
+    #[test]
+    fn save_load_delete_reference() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+        let r = Reference::new("test2024", EntryType::Article);
+        let id = r.id;
+
+        store.save_reference(&r).unwrap();
+        let loaded = store.load_reference(id).unwrap();
+        assert_eq!(loaded.cite_key, "test2024");
+
+        store.delete_reference(id).unwrap();
+        assert!(store.load_reference(id).is_err());
+    }
+
+    #[test]
+    fn list_reference_ids() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+        let r1 = Reference::new("a2024", EntryType::Article);
+        let r2 = Reference::new("b2024", EntryType::Book);
+        store.save_reference(&r1).unwrap();
+        store.save_reference(&r2).unwrap();
+
+        let ids = store.list_reference_ids().unwrap();
+        assert_eq!(ids.len(), 2);
+    }
+
+    #[test]
+    fn save_load_library() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+        let lib = Library::new("ML Papers", None);
+        let id = lib.id;
+
+        store.save_library(&lib).unwrap();
+        let loaded = store.load_library(id).unwrap();
+        assert_eq!(loaded.name, "ML Papers");
+    }
+
+    #[test]
+    fn annotations_missing_returns_empty_set() {
+        let tmp = tempfile::tempdir().unwrap();
+        let store = make_store(tmp.path());
+        let ref_id = ReferenceId::new();
+        let set = store.load_annotations(ref_id).unwrap();
+        assert!(set.annotations.is_empty());
+    }
+
+    #[test]
+    fn create_and_list_snapshot() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+
+        // Save something so there's content to commit beyond the initial commit.
+        let r = Reference::new("snap2024", EntryType::Misc);
+        store.save_reference(&r).unwrap();
+        let snap = store.create_snapshot("my first snapshot").unwrap();
+
+        let snapshots = store.list_snapshots().unwrap();
+        assert!(snapshots.iter().any(|s| s.id == snap.id));
+        assert!(snapshots.iter().any(|s| s.message == "my first snapshot"));
+    }
+
+    #[test]
+    fn restore_snapshot_reverts_state() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+
+        let r = Reference::new("before2024", EntryType::Article);
+        let ref_id = r.id;
+        store.save_reference(&r).unwrap();
+        let snap = store.create_snapshot("baseline").unwrap();
+
+        // Modify state: add another reference.
+        let r2 = Reference::new("after2024", EntryType::Book);
+        store.save_reference(&r2).unwrap();
+        assert_eq!(store.list_reference_ids().unwrap().len(), 2);
+
+        // Restore to baseline — should have only 1 reference.
+        store.restore_snapshot(&snap.id).unwrap();
+
+        let store2 = FsStore::open(tmp.path()).unwrap();
+        assert_eq!(store2.list_reference_ids().unwrap().len(), 1);
+        assert!(store2.load_reference(ref_id).is_ok());
+    }
+
+    #[test]
+    fn has_uncommitted_changes_detects_new_files() {
+        let tmp = tempfile::tempdir().unwrap();
+        let mut store = make_store(tmp.path());
+
+        assert!(!store.has_uncommitted_changes().unwrap());
+
+        let r = Reference::new("new2024", EntryType::Misc);
+        store.save_reference(&r).unwrap();
+
+        assert!(store.has_uncommitted_changes().unwrap());
+    }
+}

brittle-core/src/store/memory.rs

@@ -0,0 +1,302 @@
+use crate::error::{EntityType, StoreError};
+use crate::model::{AnnotationSet, Library, LibraryId, Reference, ReferenceId, Snapshot};
+use crate::store::Store;
+use chrono::Utc;
+use std::collections::HashMap;
+
+/// In-memory store for testing. Not suitable for production use.
+#[derive(Debug, Default)]
+pub struct MemoryStore {
+    references: HashMap<ReferenceId, Reference>,
+    libraries: HashMap<LibraryId, Library>,
+    annotations: HashMap<ReferenceId, AnnotationSet>,
+    /// Checkpoints for snapshot simulation: (id, message, cloned state).
+    snapshots: Vec<(String, String, Box<MemorySnapshot>)>,
+    next_snapshot_idx: usize,
+}
+
+#[derive(Debug)]
+struct MemorySnapshot {
+    references: HashMap<ReferenceId, Reference>,
+    libraries: HashMap<LibraryId, Library>,
+    annotations: HashMap<ReferenceId, AnnotationSet>,
+}
+
+impl MemoryStore {
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
+impl Store for MemoryStore {
+    fn save_reference(&mut self, reference: &Reference) -> Result<(), StoreError> {
+        self.references.insert(reference.id, reference.clone());
+        Ok(())
+    }
+
+    fn load_reference(&self, id: ReferenceId) -> Result<Reference, StoreError> {
+        self.references
+            .get(&id)
+            .cloned()
+            .ok_or_else(|| StoreError::NotFound {
+                entity_type: EntityType::Reference,
+                id: id.to_string(),
+            })
+    }
+
+    fn delete_reference(&mut self, id: ReferenceId) -> Result<(), StoreError> {
+        self.references
+            .remove(&id)
+            .ok_or_else(|| StoreError::NotFound {
+                entity_type: EntityType::Reference,
+                id: id.to_string(),
+            })?;
+        Ok(())
+    }
+
+    fn list_reference_ids(&self) -> Result<Vec<ReferenceId>, StoreError> {
+        Ok(self.references.keys().copied().collect())
+    }
+
+    fn save_library(&mut self, library: &Library) -> Result<(), StoreError> {
+        self.libraries.insert(library.id, library.clone());
+        Ok(())
+    }
+
+    fn load_library(&self, id: LibraryId) -> Result<Library, StoreError> {
+        self.libraries
+            .get(&id)
+            .cloned()
+            .ok_or_else(|| StoreError::NotFound {
+                entity_type: EntityType::Library,
+                id: id.to_string(),
+            })
+    }
+
+    fn delete_library(&mut self, id: LibraryId) -> Result<(), StoreError> {
+        self.libraries
+            .remove(&id)
+            .ok_or_else(|| StoreError::NotFound {
+                entity_type: EntityType::Library,
+                id: id.to_string(),
+            })?;
+        Ok(())
+    }
+
+    fn list_library_ids(&self) -> Result<Vec<LibraryId>, StoreError> {
+        Ok(self.libraries.keys().copied().collect())
+    }
+
+    fn load_annotations(&self, ref_id: ReferenceId) -> Result<AnnotationSet, StoreError> {
+        Ok(self
+            .annotations
+            .get(&ref_id)
+            .cloned()
+            .unwrap_or_else(|| AnnotationSet::new(ref_id)))
+    }
+
+    fn save_annotations(&mut self, set: &AnnotationSet) -> Result<(), StoreError> {
+        self.annotations.insert(set.reference_id, set.clone());
+        Ok(())
+    }
+
+    fn delete_annotations(&mut self, ref_id: ReferenceId) -> Result<(), StoreError> {
+        self.annotations.remove(&ref_id);
+        Ok(())
+    }
+
+    fn create_snapshot(&mut self, message: &str) -> Result<Snapshot, StoreError> {
+        let id = format!("mem-snapshot-{:04}", self.next_snapshot_idx);
+        self.next_snapshot_idx += 1;
+        let snapshot_data = Box::new(MemorySnapshot {
+            references: self.references.clone(),
+            libraries: self.libraries.clone(),
+            annotations: self.annotations.clone(),
+        });
+        let timestamp = Utc::now();
+        self.snapshots
+            .push((id.clone(), message.to_owned(), snapshot_data));
+        Ok(Snapshot {
+            id,
+            message: message.to_owned(),
+            timestamp,
+        })
+    }
+
+    fn list_snapshots(&self) -> Result<Vec<Snapshot>, StoreError> {
+        let snapshots = self
+            .snapshots
+            .iter()
+            .rev()
+            .map(|(id, message, _)| Snapshot {
+                id: id.clone(),
+                message: message.clone(),
+                timestamp: Utc::now(), // timestamps not stored in MemoryStore
+            })
+            .collect();
+        Ok(snapshots)
+    }
+
+    fn restore_snapshot(&mut self, snapshot_id: &str) -> Result<(), StoreError> {
+        let snapshot = self
+            .snapshots
+            .iter()
+            .find(|(id, _, _)| id == snapshot_id)
+            .ok_or_else(|| StoreError::NotFound {
+                entity_type: EntityType::Snapshot,
+                id: snapshot_id.to_owned(),
+            })?;
+        self.references = snapshot.2.references.clone();
+        self.libraries = snapshot.2.libraries.clone();
+        self.annotations = snapshot.2.annotations.clone();
+        Ok(())
+    }
+
+    fn has_uncommitted_changes(&self) -> Result<bool, StoreError> {
+        // MemoryStore has no concept of uncommitted changes.
+        Ok(false)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::model::{AnnotationType, EntryType, Library, Reference, TextMarkupType};
+
+    fn make_reference() -> Reference {
+        Reference::new("test2024", EntryType::Article)
+    }
+
+    fn make_library() -> Library {
+        Library::new("Test Library", None)
+    }
+
+    #[test]
+    fn save_and_load_reference() {
+        let mut store = MemoryStore::new();
+        let r = make_reference();
+        let id = r.id;
+        store.save_reference(&r).unwrap();
+        let r2 = store.load_reference(id).unwrap();
+        assert_eq!(r.cite_key, r2.cite_key);
+    }
+
+    #[test]
+    fn load_missing_reference_returns_error() {
+        let store = MemoryStore::new();
+        let id = ReferenceId::new();
+        let err = store.load_reference(id).unwrap_err();
+        assert!(matches!(
+            err,
+            StoreError::NotFound {
+                entity_type: EntityType::Reference,
+                ..
+            }
+        ));
+    }
+
+    #[test]
+    fn delete_reference() {
+        let mut store = MemoryStore::new();
+        let r = make_reference();
+        let id = r.id;
+        store.save_reference(&r).unwrap();
+        store.delete_reference(id).unwrap();
+        assert!(store.load_reference(id).is_err());
+    }
+
+    #[test]
+    fn list_reference_ids() {
+        let mut store = MemoryStore::new();
+        let r1 = make_reference();
+        let r2 = make_reference();
+        store.save_reference(&r1).unwrap();
+        store.save_reference(&r2).unwrap();
+        let ids = store.list_reference_ids().unwrap();
+        assert_eq!(ids.len(), 2);
+        assert!(ids.contains(&r1.id));
+        assert!(ids.contains(&r2.id));
+    }
+
+    #[test]
+    fn save_and_load_library() {
+        let mut store = MemoryStore::new();
+        let lib = make_library();
+        let id = lib.id;
+        store.save_library(&lib).unwrap();
+        let lib2 = store.load_library(id).unwrap();
+        assert_eq!(lib.name, lib2.name);
+    }
+
+    #[test]
+    fn delete_library() {
+        let mut store = MemoryStore::new();
+        let lib = make_library();
+        let id = lib.id;
+        store.save_library(&lib).unwrap();
+        store.delete_library(id).unwrap();
+        assert!(store.load_library(id).is_err());
+    }
+
+    #[test]
+    fn annotations_default_to_empty_set() {
+        let store = MemoryStore::new();
+        let ref_id = ReferenceId::new();
+        let set = store.load_annotations(ref_id).unwrap();
+        assert_eq!(set.reference_id, ref_id);
+        assert!(set.annotations.is_empty());
+    }
+
+    #[test]
+    fn save_and_load_annotations() {
+        use crate::model::{Annotation, Color};
+
+        let mut store = MemoryStore::new();
+        let ref_id = ReferenceId::new();
+        let ann = Annotation::new(
+            ref_id,
+            0,
+            AnnotationType::TextMarkup {
+                markup_type: TextMarkupType::Highlight,
+                quads: vec![],
+                color: Color::YELLOW,
+                selected_text: None,
+            },
+        );
+        let set = AnnotationSet {
+            reference_id: ref_id,
+            annotations: vec![ann],
+        };
+        store.save_annotations(&set).unwrap();
+        let set2 = store.load_annotations(ref_id).unwrap();
+        assert_eq!(set2.annotations.len(), 1);
+    }
+
+    #[test]
+    fn snapshot_create_and_restore() {
+        let mut store = MemoryStore::new();
+        let r = make_reference();
+        let ref_id = r.id;
+        store.save_reference(&r).unwrap();
+
+        let snap = store.create_snapshot("first snapshot").unwrap();
+
+        // Modify state after snapshot.
+        store.delete_reference(ref_id).unwrap();
+        assert!(store.load_reference(ref_id).is_err());
+
+        // Restore snapshot.
+        store.restore_snapshot(&snap.id).unwrap();
+        assert!(store.load_reference(ref_id).is_ok());
+    }
+
+    #[test]
+    fn list_snapshots_in_reverse_order() {
+        let mut store = MemoryStore::new();
+        store.create_snapshot("first").unwrap();
+        store.create_snapshot("second").unwrap();
+        let snaps = store.list_snapshots().unwrap();
+        assert_eq!(snaps.len(), 2);
+        assert_eq!(snaps[0].message, "second"); // most recent first
+    }
+}

brittle-core/src/store/mod.rs

@@ -0,0 +1,44 @@
+pub mod fs;
+pub mod memory;
+
+use crate::error::StoreError;
+use crate::model::{AnnotationSet, Library, LibraryId, Reference, ReferenceId, Snapshot};
+
+/// Abstraction over the storage backend.
+///
+/// The git-backed filesystem (`FsStore`) is the production implementation.
+/// An in-memory implementation (`MemoryStore`) exists for testing.
+pub trait Store {
+    // ---- References ----
+
+    fn save_reference(&mut self, reference: &Reference) -> Result<(), StoreError>;
+    fn load_reference(&self, id: ReferenceId) -> Result<Reference, StoreError>;
+    fn delete_reference(&mut self, id: ReferenceId) -> Result<(), StoreError>;
+    fn list_reference_ids(&self) -> Result<Vec<ReferenceId>, StoreError>;
+
+    // ---- Libraries ----
+
+    fn save_library(&mut self, library: &Library) -> Result<(), StoreError>;
+    fn load_library(&self, id: LibraryId) -> Result<Library, StoreError>;
+    fn delete_library(&mut self, id: LibraryId) -> Result<(), StoreError>;
+    fn list_library_ids(&self) -> Result<Vec<LibraryId>, StoreError>;
+
+    // ---- Annotations ----
+
+    /// Load the annotation set for a reference. Returns an empty set if none exists.
+    fn load_annotations(&self, ref_id: ReferenceId) -> Result<AnnotationSet, StoreError>;
+    fn save_annotations(&mut self, set: &AnnotationSet) -> Result<(), StoreError>;
+    fn delete_annotations(&mut self, ref_id: ReferenceId) -> Result<(), StoreError>;
+
+    // ---- Snapshots ----
+
+    fn create_snapshot(&mut self, message: &str) -> Result<Snapshot, StoreError>;
+    fn list_snapshots(&self) -> Result<Vec<Snapshot>, StoreError>;
+    /// Restore to a previous snapshot. Caller must ensure no uncommitted changes exist.
+    fn restore_snapshot(&mut self, snapshot_id: &str) -> Result<(), StoreError>;
+    fn has_uncommitted_changes(&self) -> Result<bool, StoreError>;
+}
+
+// Re-export concrete types for convenience.
+pub use fs::FsStore;
+pub use memory::MemoryStore;