diff --git a/AGENTS.md b/AGENTS.md
index bd8749d..f83866c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -96,5 +96,10 @@
 - In this monorepo, "dotfiles" refers to the dotfiles/NixOS configuration under `src/dotfiles/` and `configs/nixos/`.
 - The flake does not currently define `formatter.x86_64-linux`.
   Do not use `nix fmt` as a validation command until a formatter is added.
+- When creating a pull request from a worktree-specific development branch, create a dedicated pull-request branch
+  separate from the branch that names or anchors the worktree.
+  Do not open pull requests directly from the worktree branch.
+- Load `crate_deps` from `//third_party/crates:crates.bzl`, not `//third_party/crates:defs.bzl`.
+  The compatibility wrapper currently exports a symbol that generated `crates.bzl` does not define.
 - Ariadne extraction must preserve the game-root season prefix for archived source.
   Different game installs can contain compiled scripts with the same internal path.
diff --git a/src/ariadne/BUILD b/src/ariadne/BUILD
index c3f343f..d6e4d18 100644
--- a/src/ariadne/BUILD
+++ b/src/ariadne/BUILD
@@ -1,9 +1,17 @@
-load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_library")
+load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_library", "rust_test")
+load("//third_party/crates:crates.bzl", "crate_deps")
 
 rust_library(
     name = "ariadne_lib",
     crate_name = "ariadne",
     srcs = ["src/lib.rs"],
+    deps = crate_deps(["serde", "serde_json"]),
+)
+
+rust_test(
+    name = "ariadne_lib_test",
+    srcs = ["src/lib_test.rs"],
+    deps = [":ariadne_lib"] + crate_deps(["serde_json"]),
 )
 
 rust_binary(
diff --git a/src/ariadne/Cargo.toml b/src/ariadne/Cargo.toml
index 2d5ae86..4c5df11 100644
--- a/src/ariadne/Cargo.toml
+++ b/src/ariadne/Cargo.toml
@@ -6,3 +6,7 @@ edition = "2024"
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+
+[[test]]
+name = "ariadne_lib_test"
+path = "src/lib_test.rs"
diff --git a/src/ariadne/src/lib.rs b/src/ariadne/src/lib.rs
index 8f9e795..5e6ec8d 100644
--- a/src/ariadne/src/lib.rs
+++ b/src/ariadne/src/lib.rs
@@ -1,3 +1,285 @@
+use std::collections::{BTreeMap, BTreeSet};
+use std::error::Error;
+use std::fmt::{Display, Formatter};
+use std::fs::{self, File};
+use std::io::{BufRead, BufReader, BufWriter, Write};
+use std::path::Path;
+
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+
+pub type Metadata = BTreeMap<String, Value>;
+
+#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct NodeId(String);
+
+impl NodeId {
+    pub fn new(value: impl Into<String>) -> Self {
+        Self(value.into())
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+impl From<&str> for NodeId {
+    fn from(value: &str) -> Self {
+        Self::new(value)
+    }
+}
+
+impl From<String> for NodeId {
+    fn from(value: String) -> Self {
+        Self::new(value)
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
+pub struct SourceRef {
+    pub path: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub line: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub column: Option<u32>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Node {
+    pub id: NodeId,
+    pub kind: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub source: Option<SourceRef>,
+    pub payload: Value,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
+pub struct Edge {
+    pub from: NodeId,
+    pub to: NodeId,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "op", rename_all = "snake_case")]
+pub enum Delta {
+    AddNode { node: Node },
+    RemoveNode { node: Node },
+    ReplaceNode { old: Node, new: Node },
+    AddEdge { edge: Edge },
+    RemoveEdge { edge: Edge },
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Graph {
+    pub metadata: Metadata,
+    pub nodes: BTreeMap<NodeId, Node>,
+    pub edges: BTreeSet<Edge>,
+}
+
+impl Graph {
+    pub fn new(metadata: Metadata) -> Self {
+        Self {
+            metadata,
+            nodes: BTreeMap::new(),
+            edges: BTreeSet::new(),
+        }
+    }
+
+    pub fn add_node(&mut self, node: Node) -> Result<Delta, GraphError> {
+        if self.nodes.contains_key(&node.id) {
+            return Err(GraphError::DuplicateNode { id: node.id });
+        }
+
+        self.nodes.insert(node.id.clone(), node.clone());
+        Ok(Delta::AddNode { node })
+    }
+
+    pub fn remove_node(&mut self, id: &NodeId) -> Result<Vec<Delta>, GraphError> {
+        let node = self
+            .nodes
+            .remove(id)
+            .ok_or_else(|| GraphError::MissingNode { id: id.clone() })?;
+
+        let incident_edges: Vec<_> = self
+            .edges
+            .iter()
+            .filter(|edge| edge.from == *id || edge.to == *id)
+            .cloned()
+            .collect();
+
+        let mut deltas = Vec::with_capacity(incident_edges.len() + 1);
+        for edge in incident_edges {
+            self.edges.remove(&edge);
+            deltas.push(Delta::RemoveEdge { edge });
+        }
+        deltas.push(Delta::RemoveNode { node });
+
+        Ok(deltas)
+    }
+
+    pub fn replace_node(&mut self, node: Node) -> Result<Delta, GraphError> {
+        let old = self
+            .nodes
+            .get_mut(&node.id)
+            .ok_or_else(|| GraphError::MissingNode {
+                id: node.id.clone(),
+            })?;
+        let previous = std::mem::replace(old, node.clone());
+
+        Ok(Delta::ReplaceNode {
+            old: previous,
+            new: node,
+        })
+    }
+
+    pub fn add_edge(&mut self, edge: Edge) -> Result<Delta, GraphError> {
+        self.require_node(&edge.from)?;
+        self.require_node(&edge.to)?;
+
+        if !self.edges.insert(edge.clone()) {
+            return Err(GraphError::DuplicateEdge { edge });
+        }
+
+        Ok(Delta::AddEdge { edge })
+    }
+
+    pub fn remove_edge(&mut self, edge: &Edge) -> Result<Delta, GraphError> {
+        if !self.edges.remove(edge) {
+            return Err(GraphError::MissingEdge { edge: edge.clone() });
+        }
+
+        Ok(Delta::RemoveEdge { edge: edge.clone() })
+    }
+
+    fn require_node(&self, id: &NodeId) -> Result<(), GraphError> {
+        if self.nodes.contains_key(id) {
+            Ok(())
+        } else {
+            Err(GraphError::MissingNode { id: id.clone() })
+        }
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum GraphError {
+    DuplicateNode { id: NodeId },
+    MissingNode { id: NodeId },
+    DuplicateEdge { edge: Edge },
+    MissingEdge { edge: Edge },
+}
+
+impl Display for GraphError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            GraphError::DuplicateNode { id } => {
+                write!(formatter, "duplicate node `{}`", id.as_str())
+            }
+            GraphError::MissingNode { id } => write!(formatter, "missing node `{}`", id.as_str()),
+            GraphError::DuplicateEdge { edge } => write!(
+                formatter,
+                "duplicate edge `{} -> {}`",
+                edge.from.as_str(),
+                edge.to.as_str()
+            ),
+            GraphError::MissingEdge { edge } => write!(
+                formatter,
+                "missing edge `{} -> {}`",
+                edge.from.as_str(),
+                edge.to.as_str()
+            ),
+        }
+    }
+}
+
+impl Error for GraphError {}
+
+pub fn write_graph_artifact(
+    directory: impl AsRef<Path>,
+    graph: &Graph,
+    delta: &[Delta],
+) -> std::io::Result<()> {
+    let directory = directory.as_ref();
+    fs::create_dir_all(directory)?;
+
+    write_json_file(directory.join("metadata.json"), &graph.metadata)?;
+    write_jsonl_file(directory.join("nodes.jsonl"), graph.nodes.values())?;
+    write_jsonl_file(directory.join("edges.jsonl"), graph.edges.iter())?;
+    write_jsonl_file(directory.join("delta.jsonl"), delta.iter())?;
+
+    Ok(())
+}
+
+pub fn read_graph_artifact(directory: impl AsRef<Path>) -> std::io::Result<Graph> {
+    let directory = directory.as_ref();
+    let metadata = read_json_file(directory.join("metadata.json"))?;
+    let nodes: Vec<Node> = read_jsonl_file(directory.join("nodes.jsonl"))?;
+    let edges: Vec<Edge> = read_jsonl_file(directory.join("edges.jsonl"))?;
+
+    let mut graph = Graph::new(metadata);
+    for node in nodes {
+        graph.add_node(node).map_err(invalid_data)?;
+    }
+    for edge in edges {
+        graph.add_edge(edge).map_err(invalid_data)?;
+    }
+
+    Ok(graph)
+}
+
+pub fn read_graph_delta(directory: impl AsRef<Path>) -> std::io::Result<Vec<Delta>> {
+    read_jsonl_file(directory.as_ref().join("delta.jsonl"))
+}
+
+fn write_json_file(path: impl AsRef<Path>, value: &impl Serialize) -> std::io::Result<()> {
+    let file = File::create(path)?;
+    let writer = BufWriter::new(file);
+    serde_json::to_writer_pretty(writer, value).map_err(invalid_data)
+}
+
+fn read_json_file<T: for<'de> Deserialize<'de>>(path: impl AsRef<Path>) -> std::io::Result<T> {
+    let file = File::open(path)?;
+    let reader = BufReader::new(file);
+    serde_json::from_reader(reader).map_err(invalid_data)
+}
+
+fn write_jsonl_file<'a, T: 'a + Serialize>(
+    path: impl AsRef<Path>,
+    values: impl IntoIterator<Item = &'a T>,
+) -> std::io::Result<()> {
+    let file = File::create(path)?;
+    let mut writer = BufWriter::new(file);
+
+    for value in values {
+        serde_json::to_writer(&mut writer, value).map_err(invalid_data)?;
+        writer.write_all(b"\n")?;
+    }
+
+    Ok(())
+}
+
+fn read_jsonl_file<T: for<'de> Deserialize<'de>>(
+    path: impl AsRef<Path>,
+) -> std::io::Result<Vec<T>> {
+    let file = File::open(path)?;
+    let reader = BufReader::new(file);
+    let mut values = Vec::new();
+
+    for line in reader.lines() {
+        let line = line?;
+        if line.trim().is_empty() {
+            continue;
+        }
+        values.push(serde_json::from_str(&line).map_err(invalid_data)?);
+    }
+
+    Ok(values)
+}
+
+fn invalid_data(error: impl Error + Send + Sync + 'static) -> std::io::Error {
+    std::io::Error::new(std::io::ErrorKind::InvalidData, error)
+}
+
 pub fn run() {
     println!("Ariadne");
 }
diff --git a/src/ariadne/src/lib_test.rs b/src/ariadne/src/lib_test.rs
new file mode 100644
index 0000000..834a4c0
--- /dev/null
+++ b/src/ariadne/src/lib_test.rs
@@ -0,0 +1,129 @@
+use std::fs;
+
+use ariadne::{
+    Delta, Edge, Graph, GraphError, Metadata, Node, NodeId, read_graph_artifact, read_graph_delta,
+    write_graph_artifact,
+};
+use serde_json::json;
+
+fn node(id: &str, kind: &str) -> Node {
+    Node {
+        id: NodeId::from(id),
+        kind: kind.to_owned(),
+        source: None,
+        payload: json!({}),
+    }
+}
+
+#[test]
+fn graph_records_node_and_edge_mutations() {
+    let mut graph = Graph::new(Metadata::new());
+
+    let add_start = graph.add_node(node("start", "label")).unwrap();
+    let add_end = graph.add_node(node("end", "label")).unwrap();
+    let edge = Edge {
+        from: NodeId::from("start"),
+        to: NodeId::from("end"),
+    };
+    let add_edge = graph.add_edge(edge.clone()).unwrap();
+    let remove_edge = graph.remove_edge(&edge).unwrap();
+    let add_edge_again = graph.add_edge(edge.clone()).unwrap();
+    let replace_start = graph.replace_node(node("start", "entry_label")).unwrap();
+
+    assert_eq!(graph.nodes.len(), 2);
+    assert_eq!(graph.edges.len(), 1);
+    assert!(matches!(add_start, Delta::AddNode { .. }));
+    assert!(matches!(add_end, Delta::AddNode { .. }));
+    assert_eq!(add_edge, Delta::AddEdge { edge: edge.clone() });
+    assert_eq!(remove_edge, Delta::RemoveEdge { edge: edge.clone() });
+    assert_eq!(add_edge_again, Delta::AddEdge { edge });
+    assert_eq!(
+        replace_start,
+        Delta::ReplaceNode {
+            old: node("start", "label"),
+            new: node("start", "entry_label")
+        }
+    );
+}
+
+#[test]
+fn graph_rejects_edges_with_missing_endpoints() {
+    let mut graph = Graph::new(Metadata::new());
+    graph.add_node(node("start", "label")).unwrap();
+
+    let error = graph
+        .add_edge(Edge {
+            from: NodeId::from("start"),
+            to: NodeId::from("missing"),
+        })
+        .unwrap_err();
+
+    assert_eq!(
+        error,
+        GraphError::MissingNode {
+            id: NodeId::from("missing")
+        }
+    );
+}
+
+#[test]
+fn removing_node_records_incident_edge_removals_before_node_removal() {
+    let mut graph = Graph::new(Metadata::new());
+    graph.add_node(node("start", "label")).unwrap();
+    graph.add_node(node("end", "label")).unwrap();
+    let edge = Edge {
+        from: NodeId::from("start"),
+        to: NodeId::from("end"),
+    };
+    graph.add_edge(edge.clone()).unwrap();
+
+    let deltas = graph.remove_node(&NodeId::from("start")).unwrap();
+
+    assert_eq!(
+        deltas,
+        vec![
+            Delta::RemoveEdge { edge },
+            Delta::RemoveNode {
+                node: node("start", "label")
+            }
+        ]
+    );
+    assert!(graph.edges.is_empty());
+    assert!(!graph.nodes.contains_key(&NodeId::from("start")));
+}
+
+#[test]
+fn graph_artifact_round_trips_complete_graph_and_delta() {
+    let directory = std::env::temp_dir().join(format!(
+        "ariadne-graph-artifact-test-{}",
+        std::process::id()
+    ));
+    let _ = fs::remove_dir_all(&directory);
+
+    let mut metadata = Metadata::new();
+    metadata.insert("phase".to_owned(), json!("source"));
+    let mut graph = Graph::new(metadata);
+    let mut delta = Vec::new();
+
+    delta.push(graph.add_node(node("start", "label")).unwrap());
+    delta.push(graph.add_node(node("end", "label")).unwrap());
+    delta.push(
+        graph
+            .add_edge(Edge {
+                from: NodeId::from("start"),
+                to: NodeId::from("end"),
+            })
+            .unwrap(),
+    );
+
+    write_graph_artifact(&directory, &graph, &delta).unwrap();
+
+    assert_eq!(read_graph_artifact(&directory).unwrap(), graph);
+    assert_eq!(read_graph_delta(&directory).unwrap(), delta);
+    assert!(directory.join("metadata.json").is_file());
+    assert!(directory.join("nodes.jsonl").is_file());
+    assert!(directory.join("edges.jsonl").is_file());
+    assert!(directory.join("delta.jsonl").is_file());
+
+    fs::remove_dir_all(directory).unwrap();
+}