diff --git a/content/treehouse/vfs.tree b/content/treehouse/vfs.tree
new file mode 100644
index 0000000..e4f9a31
--- /dev/null
+++ b/content/treehouse/vfs.tree
@@ -0,0 +1,17 @@
+%% title = "treehouse virtual file system design"
+
+- notes on the design; this is not an actual listing of the virtual file system
+
+- `content` - `GitDir(".", "content")`
+
+    - `GitDir` is a special filesystem which makes all files have subpaths with commit data sourced from git.
+    their entries are ordered by how new/old a commit is
+
+        - `inner/<commit>` - contains the file content and a revision info fork
+
+        - `inner/latest` - same but for the latest revision, if applicable.
+        this may be the working tree
+
+- `template` - `PhysicalDir("template")`
+
+- `static` - `PhysicalDir("static")`
diff --git a/crates/treehouse/src/generate.rs b/crates/treehouse/src/generate.rs
index ad197bc..774c040 100644
--- a/crates/treehouse/src/generate.rs
+++ b/crates/treehouse/src/generate.rs
@@ -17,6 +17,7 @@ use serde::Serialize;
 use walkdir::WalkDir;
 
 use crate::{
+    cli::Paths,
     config::{Config, ConfigDerivedData},
     fun::seasons::Season,
     history::History,
@@ -35,8 +36,6 @@ use crate::{
 
 use crate::state::{FileId, Treehouse};
 
-use super::Paths;
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum LatestRevision {
     /// The working tree is treated as the latest revision.
diff --git a/crates/treehouse/src/lib.rs b/crates/treehouse/src/lib.rs
new file mode 100644
index 0000000..68fde5a
--- /dev/null
+++ b/crates/treehouse/src/lib.rs
@@ -0,0 +1,14 @@
+pub mod cli;
+pub mod config;
+pub mod fun;
+pub mod generate;
+pub mod history;
+pub mod html;
+pub mod import_map;
+pub mod include_static;
+pub mod parse;
+pub mod paths;
+pub mod state;
+pub mod static_urls;
+pub mod tree;
+pub mod vfs;
diff --git a/crates/treehouse/src/main.rs b/crates/treehouse/src/main.rs
index f38a216..eba04d1 100644
--- a/crates/treehouse/src/main.rs
+++ b/crates/treehouse/src/main.rs
@@ -1,28 +1,14 @@
 use std::path::Path;
 
 use clap::Parser;
-use cli::{
+use log::{error, info, warn};
+use treehouse::cli::{
     fix::{fix_all_cli, fix_file_cli},
     serve::serve,
     wc::wc_cli,
     Command, Paths, ProgramArgs,
 };
-use generate::{regenerate_or_report_error, LatestRevision};
-use log::{error, info, warn};
-
-mod cli;
-mod config;
-mod fun;
-mod generate;
-mod history;
-mod html;
-mod import_map;
-mod include_static;
-mod parse;
-mod paths;
-mod state;
-mod static_urls;
-mod tree;
+use treehouse::generate::{regenerate_or_report_error, LatestRevision};
 
 async fn fallible_main() -> anyhow::Result<()> {
     let args = ProgramArgs::parse();
diff --git a/crates/treehouse/src/vfs.rs b/crates/treehouse/src/vfs.rs
new file mode 100644
index 0000000..657093c
--- /dev/null
+++ b/crates/treehouse/src/vfs.rs
@@ -0,0 +1,151 @@
+use std::{borrow::Borrow, fmt, ops::Deref};
+
+use anyhow::ensure;
+
+pub mod empty;
+pub mod file;
+pub mod mount_points;
+pub mod physical;
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct VPath {
+    path: str,
+}
+
+impl VPath {
+    pub const SEPARATOR: char = '/';
+    pub const ROOT: &Self = unsafe { Self::new_unchecked("") };
+
+    pub fn try_new(s: &str) -> anyhow::Result<&Self> {
+        ensure!(
+            !s.ends_with(Self::SEPARATOR),
+            "path must not end with '{}'",
+            Self::SEPARATOR
+        );
+        ensure!(
+            !s.starts_with(Self::SEPARATOR),
+            "paths are always absolute and must not start with '{}'",
+            Self::SEPARATOR
+        );
+
+        Ok(unsafe { Self::new_unchecked(s) })
+    }
+
+    pub fn new(s: &str) -> &Self {
+        Self::try_new(s).expect("invalid path")
+    }
+
+    const unsafe fn new_unchecked(s: &str) -> &Self {
+        std::mem::transmute::<_, &Self>(s)
+    }
+
+    pub fn try_join(&self, sub: &str) -> anyhow::Result<VPathBuf> {
+        let mut buf = VPathBuf::from(self);
+        let sub = VPath::try_new(sub)?;
+        buf.path.push_str(&sub.path);
+        Ok(buf)
+    }
+
+    pub fn join(&self, sub: &str) -> VPathBuf {
+        self.try_join(sub).expect("invalid subpath")
+    }
+
+    pub fn strip_prefix(&self, prefix: &VPath) -> Option<&Self> {
+        self.path
+            .strip_prefix(&prefix.path)
+            .and_then(|p| p.strip_prefix('/'))
+            // SAFETY: If `self` starts with `prefix`, `p` will end up not being prefixed by `self`
+            // nor a leading slash.
+            .map(|p| unsafe { VPath::new_unchecked(p) })
+    }
+
+    pub fn depth(&self) -> usize {
+        self.path.chars().filter(|&c| c == Self::SEPARATOR).count()
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.path
+    }
+}
+
+impl ToOwned for VPath {
+    type Owned = VPathBuf;
+
+    fn to_owned(&self) -> Self::Owned {
+        VPathBuf::from(self)
+    }
+}
+
+impl fmt::Debug for VPath {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct VPathBuf {
+    path: String,
+}
+
+impl VPathBuf {
+    pub fn new(path: impl Into<String>) -> Self {
+        Self::try_new(path).expect("invalid path")
+    }
+
+    pub fn try_new(path: impl Into<String>) -> anyhow::Result<Self> {
+        let path = path.into();
+        match VPath::try_new(&path) {
+            Ok(_) => Ok(Self { path }),
+            Err(e) => Err(e),
+        }
+    }
+
+    unsafe fn new_unchecked(path: String) -> Self {
+        Self { path }
+    }
+}
+
+impl Deref for VPathBuf {
+    type Target = VPath;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { VPath::new_unchecked(&self.path) }
+    }
+}
+
+impl fmt::Debug for VPathBuf {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.path)
+    }
+}
+
+impl From<&VPath> for VPathBuf {
+    fn from(value: &VPath) -> Self {
+        unsafe { Self::new_unchecked(value.path.to_owned()) }
+    }
+}
+
+impl Borrow<VPath> for VPathBuf {
+    fn borrow(&self) -> &VPath {
+        self
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DirEntry {
+    pub path: VPathBuf,
+}
+
+pub trait ReadFilesystem {
+    /// List all files under the provided path.
+    fn dir(&self, path: &VPath) -> Vec<DirEntry>;
+
+    /// Get a string signifying the current version of the provided path's content.
+    /// If the content changes, the version must also change.
+    ///
+    /// Returns None if there is no content or no version string is available.
+    fn content_version(&self, path: &VPath) -> Option<String>;
+
+    /// Return the byte content of the entry at the given path.
+    fn content(&self, path: &VPath) -> Option<Vec<u8>>;
+}
diff --git a/crates/treehouse/src/vfs/empty.rs b/crates/treehouse/src/vfs/empty.rs
new file mode 100644
index 0000000..f738900
--- /dev/null
+++ b/crates/treehouse/src/vfs/empty.rs
@@ -0,0 +1,17 @@
+use super::{DirEntry, ReadFilesystem, VPath};
+
+pub struct EmptyFilesystem;
+
+impl ReadFilesystem for EmptyFilesystem {
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        vec![]
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        None
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        None
+    }
+}
diff --git a/crates/treehouse/src/vfs/file.rs b/crates/treehouse/src/vfs/file.rs
new file mode 100644
index 0000000..af4f79d
--- /dev/null
+++ b/crates/treehouse/src/vfs/file.rs
@@ -0,0 +1,30 @@
+use super::{DirEntry, ReadFilesystem, VPath};
+
+pub struct BufferedFile {
+    pub content: Vec<u8>,
+}
+
+impl BufferedFile {
+    pub fn new(content: Vec<u8>) -> Self {
+        Self { content }
+    }
+}
+
+impl ReadFilesystem for BufferedFile {
+    fn dir(&self, _path: &VPath) -> Vec<DirEntry> {
+        vec![]
+    }
+
+    fn content_version(&self, _path: &VPath) -> Option<String> {
+        // TODO: StaticFile should _probably_ calculate a content_version.
+        None
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        if path == VPath::ROOT {
+            Some(self.content.clone())
+        } else {
+            None
+        }
+    }
+}
diff --git a/crates/treehouse/src/vfs/mount_points.rs b/crates/treehouse/src/vfs/mount_points.rs
new file mode 100644
index 0000000..7950f29
--- /dev/null
+++ b/crates/treehouse/src/vfs/mount_points.rs
@@ -0,0 +1,92 @@
+use std::collections::HashMap;
+
+use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+
+pub struct MountPoints {
+    mount_points: HashMap<String, Box<dyn ReadFilesystem>>,
+}
+
+enum Resolved<'fs, 'path> {
+    Root,
+    MountPoint {
+        fs: &'fs dyn ReadFilesystem,
+        subpath: &'path VPath,
+    },
+    None,
+}
+
+impl MountPoints {
+    pub fn new() -> Self {
+        Self {
+            mount_points: HashMap::new(),
+        }
+    }
+
+    pub fn add(&mut self, path: &VPath, fs: Box<dyn ReadFilesystem>) {
+        assert_eq!(
+            path.depth(), 0,
+            "path must be situated at root. MountPoints does not support nested paths, but you can nest MountPoints within other MountPoints"
+        );
+
+        assert!(
+            self.mount_points
+                .insert(path.as_str().to_owned(), fs)
+                .is_none(),
+            "duplicate mount point at {path:?}"
+        );
+    }
+
+    fn resolve<'fs, 'path>(&'fs self, path: &'path VPath) -> Resolved<'fs, 'path> {
+        if path == VPath::ROOT {
+            return Resolved::Root;
+        } else {
+            let mount_point_name = path.as_str().split(VPath::SEPARATOR).next().unwrap();
+            if let Some(mount_point) = self.mount_points.get(mount_point_name) {
+                return Resolved::MountPoint {
+                    fs: &**mount_point,
+                    subpath: path
+                        .strip_prefix(VPath::new(mount_point_name))
+                        .expect("path should have `mount_point_name` as its prefix"),
+                };
+            }
+        }
+
+        Resolved::None
+    }
+}
+
+impl Default for MountPoints {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ReadFilesystem for MountPoints {
+    fn dir(&self, path: &VPath) -> Vec<DirEntry> {
+        match self.resolve(path) {
+            Resolved::Root => self
+                .mount_points
+                .keys()
+                .map(|name| DirEntry {
+                    path: VPathBuf::new(name),
+                })
+                .collect(),
+            Resolved::MountPoint { fs, subpath } => fs.dir(subpath),
+            Resolved::None => vec![],
+        }
+    }
+
+    fn content_version(&self, path: &VPath) -> Option<String> {
+        match self.resolve(path) {
+            Resolved::MountPoint { fs, subpath } => fs.content_version(subpath),
+            Resolved::Root | Resolved::None => None,
+        }
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        match self.resolve(path) {
+            Resolved::MountPoint { fs, subpath } => fs.content(subpath),
+            Resolved::Root | Resolved::None => None,
+        }
+    }
+}
diff --git a/crates/treehouse/src/vfs/physical.rs b/crates/treehouse/src/vfs/physical.rs
new file mode 100644
index 0000000..64c13f2
--- /dev/null
+++ b/crates/treehouse/src/vfs/physical.rs
@@ -0,0 +1,78 @@
+use std::path::{Path, PathBuf};
+
+use log::error;
+
+use super::{DirEntry, ReadFilesystem, VPath, VPathBuf};
+
+#[derive(Debug, Clone)]
+pub struct PhysicalDir {
+    root: PathBuf,
+}
+
+impl PhysicalDir {
+    pub fn new(root: PathBuf) -> Self {
+        Self { root }
+    }
+}
+
+impl ReadFilesystem for PhysicalDir {
+    fn dir(&self, vpath: &VPath) -> Vec<DirEntry> {
+        let physical = self.root.join(physical_path(vpath));
+        match std::fs::read_dir(physical) {
+            Ok(read_dir) => read_dir
+                .filter_map(|entry| {
+                    entry
+                        .inspect_err(|err| {
+                            error!(
+                                "PhysicalDir {:?} error while reading entries in vpath {vpath:?}: {err:?}",
+                                self.root
+                            )
+                        })
+                        .ok()
+                        .and_then(|entry| {
+                            let path = entry.path();
+                            let path_str = match path.strip_prefix(&self.root).unwrap_or(&path).to_str() {
+                                Some(p) => p,
+                                None => {
+                                    error!("PhysicalDir {:?} entry {path:?} has invalid UTF-8 (while reading vpath {vpath:?})", self.root);
+                                    return None;
+                                },
+                            };
+                            let vpath_buf = VPathBuf::try_new(path_str.replace('\\', "/"))
+                                .inspect_err(|err| {
+                                    error!("PhysicalDir {:?} error with vpath for {path_str:?}: {err:?}", self.root);
+                                })
+                                .ok()?;
+                            Some(DirEntry { path: vpath_buf })
+                        })
+                })
+                .collect(),
+            Err(err) => {
+                error!(
+                    "PhysicalDir {:?} cannot read vpath {vpath:?}: {err:?}",
+                    self.root
+                );
+                vec![]
+            }
+        }
+    }
+
+    fn content_version(&self, _path: &VPath) -> Option<String> {
+        None
+    }
+
+    fn content(&self, path: &VPath) -> Option<Vec<u8>> {
+        std::fs::read(self.root.join(physical_path(path)))
+            .inspect_err(|err| {
+                error!(
+                    "PhysicalDir {:?} cannot read file at vpath {path:?}: {err:?}",
+                    self.root
+                )
+            })
+            .ok()
+    }
+}
+
+fn physical_path(path: &VPath) -> &Path {
+    Path::new(path.as_str())
+}
diff --git a/crates/treehouse/tests/it/main.rs b/crates/treehouse/tests/it/main.rs
new file mode 100644
index 0000000..03a9976
--- /dev/null
+++ b/crates/treehouse/tests/it/main.rs
@@ -0,0 +1 @@
+mod vfs;
diff --git a/crates/treehouse/tests/it/vfs.rs b/crates/treehouse/tests/it/vfs.rs
new file mode 100644
index 0000000..6c6651c
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs.rs
@@ -0,0 +1,4 @@
+mod empty;
+mod file;
+mod mount_points;
+mod physical;
diff --git a/crates/treehouse/tests/it/vfs/empty.rs b/crates/treehouse/tests/it/vfs/empty.rs
new file mode 100644
index 0000000..48205d1
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs/empty.rs
@@ -0,0 +1,16 @@
+use treehouse::vfs::{empty::EmptyFilesystem, ReadFilesystem, VPath};
+
+#[test]
+fn dir() {
+    assert!(EmptyFilesystem.dir(VPath::ROOT).is_empty());
+}
+
+#[test]
+fn content_version() {
+    assert!(EmptyFilesystem.content_version(VPath::ROOT).is_none());
+}
+
+#[test]
+fn content() {
+    assert!(EmptyFilesystem.content(VPath::ROOT).is_none());
+}
diff --git a/crates/treehouse/tests/it/vfs/file.rs b/crates/treehouse/tests/it/vfs/file.rs
new file mode 100644
index 0000000..8eeee4c
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs/file.rs
@@ -0,0 +1,29 @@
+use treehouse::vfs::{file::BufferedFile, ReadFilesystem, VPath};
+
+fn vfs() -> BufferedFile {
+    BufferedFile::new(b"hewwo :3".to_vec())
+}
+
+#[test]
+fn dir() {
+    let vfs = vfs();
+    assert!(vfs.dir(VPath::ROOT).is_empty());
+}
+
+#[test]
+fn content_version() {
+    let vfs = vfs();
+    assert!(
+        vfs.content_version(VPath::ROOT).is_none(),
+        "content_version is not implemented for BufferedFile for now"
+    );
+}
+
+#[test]
+fn content() {
+    let vfs = vfs();
+    assert_eq!(
+        vfs.content(VPath::ROOT).as_deref(),
+        Some(b"hewwo :3".as_slice()),
+    );
+}
diff --git a/crates/treehouse/tests/it/vfs/mount_points.rs b/crates/treehouse/tests/it/vfs/mount_points.rs
new file mode 100644
index 0000000..ca6747f
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs/mount_points.rs
@@ -0,0 +1,50 @@
+use std::path::Path;
+
+use treehouse::vfs::{
+    file::BufferedFile, mount_points::MountPoints, physical::PhysicalDir, DirEntry, ReadFilesystem,
+    VPath, VPathBuf,
+};
+
+fn vfs() -> MountPoints {
+    let file1 = BufferedFile::new(b"hewwo :3".to_vec());
+    let file2 = BufferedFile::new(b"fwoofee -w-".to_vec());
+    let file3 = BufferedFile::new(b"boop >w<".to_vec());
+
+    let mut inner = MountPoints::new();
+    inner.add(VPath::new("file3.txt"), Box::new(file3));
+
+    let mut vfs = MountPoints::new();
+    vfs.add(VPath::new("file1.txt"), Box::new(file1));
+    vfs.add(VPath::new("file2.txt"), Box::new(file2));
+    vfs.add(VPath::new("inner"), Box::new(inner));
+    vfs
+}
+
+#[test]
+fn dir() {
+    let vfs = vfs();
+
+    assert_eq!(
+        vfs.dir(VPath::new("")),
+        vec![
+            DirEntry {
+                path: VPathBuf::new("file1.txt"),
+            },
+            DirEntry {
+                path: VPathBuf::new("file2.txt"),
+            },
+            DirEntry {
+                path: VPathBuf::new("inner"),
+            }
+        ]
+    );
+
+    assert!(vfs.dir(VPath::new("file1.txt")).is_empty());
+    assert!(vfs.dir(VPath::new("file2.txt")).is_empty());
+    assert_eq!(
+        vfs.dir(VPath::new("inner")),
+        vec![DirEntry {
+            path: VPathBuf::new("file3.txt")
+        }]
+    );
+}
diff --git a/crates/treehouse/tests/it/vfs/physical.rs b/crates/treehouse/tests/it/vfs/physical.rs
new file mode 100644
index 0000000..6c6f857
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs/physical.rs
@@ -0,0 +1,37 @@
+use std::path::Path;
+
+use treehouse::vfs::{physical::PhysicalDir, DirEntry, ReadFilesystem, VPath, VPathBuf};
+
+fn vfs() -> PhysicalDir {
+    let root = Path::new("tests/it/vfs_physical").to_path_buf();
+    PhysicalDir::new(root)
+}
+
+#[test]
+fn dir() {
+    let vfs = vfs();
+    let dir = vfs.dir(VPath::ROOT);
+    assert_eq!(
+        &dir[..],
+        &[DirEntry {
+            path: VPathBuf::new("test.txt"),
+        }]
+    );
+}
+
+#[test]
+fn content_version() {
+    let vfs = vfs();
+    let content_version = vfs.content_version(VPath::new("test.txt"));
+    assert_eq!(
+        content_version, None,
+        "content_version remains unimplemented for now"
+    );
+}
+
+#[test]
+fn content() {
+    let vfs = vfs();
+    let content = vfs.content(VPath::new("test.txt"));
+    assert_eq!(content.as_deref(), Some(b"hewwo :3\n".as_slice()));
+}
diff --git a/crates/treehouse/tests/it/vfs_physical/test.txt b/crates/treehouse/tests/it/vfs_physical/test.txt
new file mode 100644
index 0000000..73dca14
--- /dev/null
+++ b/crates/treehouse/tests/it/vfs_physical/test.txt
@@ -0,0 +1 @@
+hewwo :3