From 60e66465430c87d2794b45edc6e8a9212e6ef8fe Mon Sep 17 00:00:00 2001
From: Mike Bostock <mbostock@gmail.com>
Date: Fri, 15 Mar 2024 09:01:56 -0700
Subject: [PATCH 1/3] fix describe{Tables,Columns} (#1068)

---
 src/client/stdlib/duckdb.js | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/client/stdlib/duckdb.js b/src/client/stdlib/duckdb.js
index 6f14b3487..09420378f 100644
--- a/src/client/stdlib/duckdb.js
+++ b/src/client/stdlib/duckdb.js
@@ -146,18 +146,19 @@ export class DuckDBClient {
   }
 
   async describeTables() {
-    const tables = await this.query("SHOW TABLES");
-    return tables.map(({name}) => ({name}));
+    return Array.from(await this.query("SHOW TABLES"), ({name}) => ({name}));
   }
 
   async describeColumns({table} = {}) {
-    const columns = await this.query(`DESCRIBE ${this.escape(table)}`);
-    return columns.map(({column_name, column_type, null: nullable}) => ({
-      name: column_name,
-      type: getDuckDBType(column_type),
-      nullable: nullable !== "NO",
-      databaseType: column_type
-    }));
+    return Array.from(
+      await this.query(`DESCRIBE ${this.escape(table)}`),
+      ({column_name, column_type, null: nullable}) => ({
+        name: column_name,
+        type: getDuckDBType(column_type),
+        nullable: nullable !== "NO",
+        databaseType: column_type
+      })
+    );
   }
 
   static async of(sources = {}, config = {}) {

From 1971b567b103d948fa51c8c1ced72407c768fa05 Mon Sep 17 00:00:00 2001
From: Mike Bostock <mbostock@gmail.com>
Date: Fri, 15 Mar 2024 09:03:03 -0700
Subject: [PATCH 2/3] fix resolveScript during build (#1069)

---
 src/build.ts                          | 5 +++++
 test/output/build/imports/script.html | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/build.ts b/src/build.ts
index b1b88718f..52fdc7697 100644
--- a/src/build.ts
+++ b/src/build.ts
@@ -238,6 +238,11 @@ export async function build(
           const r = resolvers.resolveImport(specifier);
           const a = aliases.get(resolvePath(path, r));
           return a ? relativePath(path, a) : isPathImport(specifier) ? specifier : r; // fallback to specifier if enoent
+        },
+        resolveScript(specifier) {
+          const r = resolvers.resolveScript(specifier);
+          const a = aliases.get(resolvePath(path, r));
+          return a ? relativePath(path, a) : specifier; // fallback to specifier if enoent
         }
       }
     });
diff --git a/test/output/build/imports/script.html b/test/output/build/imports/script.html
index 510ccd227..cfd0511db 100644
--- a/test/output/build/imports/script.html
+++ b/test/output/build/imports/script.html
@@ -36,7 +36,7 @@
 <div id="observablehq-center">
 <main id="observablehq-main" class="observablehq">
 <h1 id="scripts" tabindex="-1"><a class="observablehq-header-anchor" href="#scripts">Scripts</a></h1>
-<script src="./_import/top.js?sha=160847a6b4890d59f8e8862911bfbe3b8066955d31f2708cafbe51945c3c57b6" type="module"></script>
+<script src="./_import/top.160847a6.js" type="module"></script>
 <script src="./_file/top.a53c5d5b.js" type="other"></script>
 </main>
 <footer id="observablehq-footer">

From 6586877e83f61230c5435f77a3b18f8b8adc4fda Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Rivi=C3=A8re?= <fil@rezo.net>
Date: Fri, 15 Mar 2024 17:33:21 +0100
Subject: [PATCH 3/3] lastModified (#1051)

* tests

* document

* fileAttachment knows about lastModified

* build tests know about lastModified

* lastModified

* lastModified and content hash are now based on a data loader's cached payload

* minimize diff

* lowercase comment

* Apply suggestions from code review

Co-authored-by: Mike Bostock <mbostock@gmail.com>

* fix LoaderResolver.getLastModified logic & add tests

* okay this is a fake data loader, but let's keep it consistent

* restore default mime-type but on render instead of in the client/stdlib

* move the default mime-type back to the client; the test doesn't have it anymore

* javadoc comment

---------

Co-authored-by: Mike Bostock <mbostock@gmail.com>
---
 docs/javascript/files.md                      |  6 ++--
 src/client/stdlib/fileAttachment.js           | 13 ++++----
 src/dataloader.ts                             | 31 ++++++++++++++---
 src/render.ts                                 | 18 ++++++----
 src/resolvers.ts                              |  3 +-
 test/build-test.ts                            |  1 +
 test/dataloaders-test.ts                      | 33 ++++++++++++++++++-
 test/input/build/files/files.md               |  4 +++
 test/input/loader/cached.txt.sh               |  1 +
 test/input/loader/not-cached.txt.sh           |  1 +
 test/input/loader/simple.txt                  |  1 +
 test/output/build/archives.posix/tar.html     | 14 ++++----
 test/output/build/archives.posix/zip.html     |  8 ++---
 test/output/build/archives.win32/tar.html     |  6 ++--
 test/output/build/archives.win32/zip.html     |  4 +--
 test/output/build/fetches/foo.html            |  4 +--
 test/output/build/fetches/top.html            |  8 ++---
 test/output/build/files/files.html            | 14 ++++++--
 .../build/files/subsection/subfiles.html      |  4 +--
 test/output/build/imports/foo/foo.html        |  2 +-
 test/output/build/multi/index.html            |  4 +--
 test/output/build/simple/simple.html          |  2 +-
 22 files changed, 129 insertions(+), 53 deletions(-)
 create mode 100644 test/input/loader/cached.txt.sh
 create mode 100644 test/input/loader/not-cached.txt.sh
 create mode 100644 test/input/loader/simple.txt

diff --git a/docs/javascript/files.md b/docs/javascript/files.md
index 1d14a19c4..86f09b2f0 100644
--- a/docs/javascript/files.md
+++ b/docs/javascript/files.md
@@ -10,7 +10,7 @@ Load files — whether static or generated dynamically by a [data loader](../loa
 import {FileAttachment} from "npm:@observablehq/stdlib";
 ```
 
-The `FileAttachment` function takes a path and returns a file handle. This handle exposes the file’s name and [MIME type](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types).
+The `FileAttachment` function takes a path and returns a file handle. This handle exposes the file’s name, [MIME type](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types), and last modification date as the number of milliseconds since UNIX epoch.
 
 ```js echo
 FileAttachment("volcano.json")
@@ -32,7 +32,7 @@ volcano
 
 ### Static analysis
 
-The `FileAttachment` function can _only_ be passed a static string literal; constructing a dynamic path such as `FileAttachment("my" + "file.csv")` is invalid syntax. Static analysis is used to invoke [data loaders](../loaders) at build time, and ensures that only referenced files are included in the generated output during build. In the future [#260](https://github.com/observablehq/framework/issues/260), it will also allow content hashes for cache breaking during deploy.
+The `FileAttachment` function can _only_ be passed a static string literal; constructing a dynamic path such as `FileAttachment("my" + "file.csv")` is invalid syntax. Static analysis is used to invoke [data loaders](../loaders) at build time, and ensures that only referenced files are included in the generated output during build. This also allows a content hash in the file name for cache breaking during deploy.
 
 If you have multiple files, you can enumerate them explicitly like so:
 
@@ -52,6 +52,8 @@ const frames = [
 
 None of the files in `frames` above are loaded until a [content method](#supported-formats) is invoked, for example by saying `frames[0].image()`.
 
+For missing files, `file.lastModified` is undefined. The `file.mimeType` is determined by checking the file extension against the [`mime-db` media type database](https://github.com/jshttp/mime-db); it defaults to `application/octet-stream`.
+
 ## Supported formats
 
 `FileAttachment` supports a variety of methods for loading file contents:
diff --git a/src/client/stdlib/fileAttachment.js b/src/client/stdlib/fileAttachment.js
index 94156052e..7421bfb6a 100644
--- a/src/client/stdlib/fileAttachment.js
+++ b/src/client/stdlib/fileAttachment.js
@@ -11,8 +11,8 @@ export function FileAttachment(name, base = location.href) {
   const url = new URL(name, base).href;
   const file = files.get(url);
   if (!file) throw new Error(`File not found: ${name}`);
-  const {path, mimeType} = file;
-  return new FileAttachmentImpl(new URL(path, location).href, name.split("/").pop(), mimeType);
+  const {path, mimeType, lastModified} = file;
+  return new FileAttachmentImpl(new URL(path, location).href, name.split("/").pop(), mimeType, lastModified);
 }
 
 async function remote_fetch(file) {
@@ -28,9 +28,10 @@ async function dsv(file, delimiter, {array = false, typed = false} = {}) {
 }
 
 export class AbstractFile {
-  constructor(name, mimeType = "application/octet-stream") {
-    Object.defineProperty(this, "name", {value: `${name}`, enumerable: true});
+  constructor(name, mimeType = "application/octet-stream", lastModified) {
     Object.defineProperty(this, "mimeType", {value: `${mimeType}`, enumerable: true});
+    Object.defineProperty(this, "name", {value: `${name}`, enumerable: true});
+    if (lastModified !== undefined) Object.defineProperty(this, "lastModified", {value: Number(lastModified), enumerable: true}); // prettier-ignore
   }
   async blob() {
     return (await remote_fetch(this)).blob();
@@ -95,8 +96,8 @@ export class AbstractFile {
 }
 
 class FileAttachmentImpl extends AbstractFile {
-  constructor(url, name, mimeType) {
-    super(name, mimeType);
+  constructor(url, name, mimeType, lastModified) {
+    super(name, mimeType, lastModified);
     Object.defineProperty(this, "_url", {value: url});
   }
   async url() {
diff --git a/src/dataloader.ts b/src/dataloader.ts
index 18e41b674..4ff211279 100644
--- a/src/dataloader.ts
+++ b/src/dataloader.ts
@@ -7,7 +7,7 @@ import JSZip from "jszip";
 import {extract} from "tar-stream";
 import {maybeStat, prepareOutput} from "./files.js";
 import {FileWatchers} from "./fileWatchers.js";
-import {getFileHash} from "./javascript/module.js";
+import {getFileHash, getFileInfo} from "./javascript/module.js";
 import type {Logger, Writer} from "./logger.js";
 import {cyan, faint, green, red, yellow} from "./tty.js";
 
@@ -129,12 +129,35 @@ export class LoaderResolver {
     return FileWatchers.of(this, path, watchPaths, callback);
   }
 
-  getFileHash(path: string): string {
+  /**
+   * Get the actual path of a file. For data loaders, it is the output if
+   * already available (cached). In build this is always the case (unless the
+   * corresponding data loader fails). However in preview we return the page
+   * before running the data loaders (which will run on demand from the page),
+   * so there might be a temporary discrepancy when a cache is stale.
+   */
+  private getFilePath(name: string): string {
+    let path = name;
     if (!existsSync(join(this.root, path))) {
       const loader = this.find(path);
-      if (loader) path = relative(this.root, loader.path);
+      if (loader) {
+        path = relative(this.root, loader.path);
+        if (name !== path) {
+          const cachePath = join(".observablehq", "cache", name);
+          if (existsSync(join(this.root, cachePath))) path = cachePath;
+        }
+      }
     }
-    return getFileHash(this.root, path);
+    return path;
+  }
+
+  getFileHash(name: string): string {
+    return getFileHash(this.root, this.getFilePath(name));
+  }
+
+  getLastModified(name: string): number | undefined {
+    const entry = getFileInfo(this.root, this.getFilePath(name));
+    return entry && Math.floor(entry.mtimeMs);
   }
 
   resolveFilePath(path: string): string {
diff --git a/src/render.ts b/src/render.ts
index c895f34fc..8672a8ef1 100644
--- a/src/render.ts
+++ b/src/render.ts
@@ -8,7 +8,7 @@ import {transpileJavaScript} from "./javascript/transpile.js";
 import type {MarkdownPage} from "./markdown.js";
 import type {PageLink} from "./pager.js";
 import {findLink, normalizePath} from "./pager.js";
-import {relativePath} from "./path.js";
+import {relativePath, resolvePath} from "./path.js";
 import type {Resolvers} from "./resolvers.js";
 import {getResolvers} from "./resolvers.js";
 import {rollupClient} from "./rollup.js";
@@ -25,7 +25,8 @@ type RenderInternalOptions =
 
 export async function renderPage(page: MarkdownPage, options: RenderOptions & RenderInternalOptions): Promise<string> {
   const {data} = page;
-  const {root, md, base, path, pages, title, preview, search, resolvers = await getResolvers(page, options)} = options;
+  const {root, md, base, path, pages, title, preview, search} = options;
+  const {loaders, resolvers = await getResolvers(page, options)} = options;
   const {normalizeLink} = md;
   const sidebar = data?.sidebar !== undefined ? Boolean(data.sidebar) : options.sidebar;
   const toc = mergeToc(data?.toc, options.toc);
@@ -63,7 +64,9 @@ import ${preview || page.code.length ? `{${preview ? "open, " : ""}define} from
         )};`
       : ""
   }${data?.sql ? `\nimport {registerTable} from ${JSON.stringify(resolveImport("npm:@observablehq/duckdb"))};` : ""}${
-    files.size ? `\n${renderFiles(files, resolveFile)}` : ""
+    files.size
+      ? `\n${renderFiles(files, resolveFile, (name: string) => loaders.getLastModified(resolvePath(path, name)))}`
+      : ""
   }${
     data?.sql
       ? `\n${Object.entries<string>(data.sql)
@@ -84,18 +87,19 @@ ${html.unsafe(rewriteHtml(page.html, resolvers))}</main>${renderFooter(path, opt
 `);
 }
 
-function renderFiles(files: Iterable<string>, resolve: (name: string) => string): string {
+function renderFiles(files: Iterable<string>, resolve: (name: string) => string, getLastModified): string {
   return Array.from(files)
     .sort()
-    .map((f) => renderFile(f, resolve))
+    .map((f) => renderFile(f, resolve, getLastModified))
     .join("");
 }
 
-function renderFile(name: string, resolve: (name: string) => string): string {
+function renderFile(name: string, resolve: (name: string) => string, getLastModified): string {
   return `\nregisterFile(${JSON.stringify(name)}, ${JSON.stringify({
     name,
     mimeType: mime.getType(name) ?? undefined,
-    path: resolve(name)
+    path: resolve(name),
+    lastModified: getLastModified(name)
   })});`;
 }
 
diff --git a/src/resolvers.ts b/src/resolvers.ts
index bde853a5a..3e231ef63 100644
--- a/src/resolvers.ts
+++ b/src/resolvers.ts
@@ -114,8 +114,7 @@ export async function getResolvers(
     }
   }
 
-  // Compute the content hash. TODO In build, this needs to consider the output
-  // of data loaders, rather than the source of data loaders.
+  // Compute the content hash.
   for (const f of assets) hash.update(loaders.getFileHash(resolvePath(path, f)));
   for (const f of files) hash.update(loaders.getFileHash(resolvePath(path, f)));
   for (const i of localImports) hash.update(getModuleHash(root, resolvePath(path, i)));
diff --git a/test/build-test.ts b/test/build-test.ts
index 5271831da..e6f68c5f0 100644
--- a/test/build-test.ts
+++ b/test/build-test.ts
@@ -101,6 +101,7 @@ class TestEffects extends FileBuildEffects {
   async writeFile(outputPath: string, contents: string | Buffer): Promise<void> {
     if (typeof contents === "string" && outputPath.endsWith(".html")) {
       contents = contents.replace(/^(\s*<script>\{).*(\}<\/script>)$/gm, "$1/* redacted init script */$2");
+      contents = contents.replace(/^(registerFile\(.*,"lastModified":)\d+(\}\);)$/gm, "$1/* ts */1706742000000$2");
     }
     return super.writeFile(outputPath, contents);
   }
diff --git a/test/dataloaders-test.ts b/test/dataloaders-test.ts
index 0059519b5..af2b13855 100644
--- a/test/dataloaders-test.ts
+++ b/test/dataloaders-test.ts
@@ -1,5 +1,5 @@
 import assert from "node:assert";
-import {readFile, stat, unlink, utimes} from "node:fs/promises";
+import {mkdir, readFile, rmdir, stat, unlink, utimes, writeFile} from "node:fs/promises";
 import os from "node:os";
 import type {LoadEffects} from "../src/dataloader.js";
 import {LoaderResolver} from "../src/dataloader.js";
@@ -113,3 +113,34 @@ describe("LoaderResolver.getFileHash(path)", () => {
     assert.strictEqual(loaders.getFileHash("does-not-exist.csv"), "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"); // prettier-ignore
   });
 });
+
+describe("LoaderResolver.getLastModified(path)", () => {
+  const time1 = new Date(Date.UTC(2023, 11, 1));
+  const time2 = new Date(Date.UTC(2024, 2, 1));
+  const loaders = new LoaderResolver({root: "test"});
+  it("returns the last modification time for a simple file", async () => {
+    await utimes("test/input/loader/simple.txt", time1, time1);
+    assert.strictEqual(loaders.getLastModified("input/loader/simple.txt"), +time1);
+  });
+  it("returns an undefined last modification time for a missing file", async () => {
+    assert.strictEqual(loaders.getLastModified("input/loader/missing.txt"), undefined);
+  });
+  it("returns the last modification time for a cached data loader", async () => {
+    await utimes("test/input/loader/cached.txt.sh", time1, time1);
+    await mkdir("test/.observablehq/cache/input/loader/", {recursive: true});
+    await writeFile("test/.observablehq/cache/input/loader/cached.txt", "2024-03-01 00:00:00");
+    await utimes("test/.observablehq/cache/input/loader/cached.txt", time2, time2);
+    assert.strictEqual(loaders.getLastModified("input/loader/cached.txt"), +time2);
+    // clean up
+    try {
+      await unlink("test/.observablehq/cache/input/loader/cached.txt");
+      await rmdir("test/.observablehq/cache/input/loader", {recursive: true});
+    } catch {
+      // ignore;
+    }
+  });
+  it("returns the last modification time for a data loader that has no cache", async () => {
+    await utimes("test/input/loader/not-cached.txt.sh", time1, time1);
+    assert.strictEqual(loaders.getLastModified("input/loader/not-cached.txt"), +time1);
+  });
+});
diff --git a/test/input/build/files/files.md b/test/input/build/files/files.md
index 55f704321..879c67347 100644
--- a/test/input/build/files/files.md
+++ b/test/input/build/files/files.md
@@ -14,6 +14,10 @@ FileAttachment("subsection/file-sub.csv")
 FileAttachment("observable logo.png")
 ```
 
+```js
+FileAttachment("unknown-mime-extension.really")
+```
+
 ![](observable%20logo%20small.png)
 
 
diff --git a/test/input/loader/cached.txt.sh b/test/input/loader/cached.txt.sh
new file mode 100644
index 000000000..371bce084
--- /dev/null
+++ b/test/input/loader/cached.txt.sh
@@ -0,0 +1 @@
+date -u "+%Y-%m-%d %H:%M:%S"
diff --git a/test/input/loader/not-cached.txt.sh b/test/input/loader/not-cached.txt.sh
new file mode 100644
index 000000000..371bce084
--- /dev/null
+++ b/test/input/loader/not-cached.txt.sh
@@ -0,0 +1 @@
+date -u "+%Y-%m-%d %H:%M:%S"
diff --git a/test/input/loader/simple.txt b/test/input/loader/simple.txt
new file mode 100644
index 000000000..e427984d4
--- /dev/null
+++ b/test/input/loader/simple.txt
@@ -0,0 +1 @@
+HELLO
diff --git a/test/output/build/archives.posix/tar.html b/test/output/build/archives.posix/tar.html
index a5f89fe9d..58f7e6faf 100644
--- a/test/output/build/archives.posix/tar.html
+++ b/test/output/build/archives.posix/tar.html
@@ -15,13 +15,13 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./dynamic-tar-gz/does-not-exist.txt", {"name":"./dynamic-tar-gz/does-not-exist.txt","mimeType":"text/plain","path":"./dynamic-tar-gz/does-not-exist.txt"});
-registerFile("./dynamic-tar-gz/file.txt", {"name":"./dynamic-tar-gz/file.txt","mimeType":"text/plain","path":"./_file/dynamic-tar-gz/file.c93138d8.txt"});
-registerFile("./dynamic-tar/does-not-exist.txt", {"name":"./dynamic-tar/does-not-exist.txt","mimeType":"text/plain","path":"./dynamic-tar/does-not-exist.txt"});
-registerFile("./dynamic-tar/file.txt", {"name":"./dynamic-tar/file.txt","mimeType":"text/plain","path":"./_file/dynamic-tar/file.c93138d8.txt"});
-registerFile("./static-tar/does-not-exist.txt", {"name":"./static-tar/does-not-exist.txt","mimeType":"text/plain","path":"./static-tar/does-not-exist.txt"});
-registerFile("./static-tar/file.txt", {"name":"./static-tar/file.txt","mimeType":"text/plain","path":"./_file/static-tar/file.c93138d8.txt"});
-registerFile("./static-tgz/file.txt", {"name":"./static-tgz/file.txt","mimeType":"text/plain","path":"./_file/static-tgz/file.c93138d8.txt"});
+registerFile("./dynamic-tar-gz/does-not-exist.txt", {"name":"./dynamic-tar-gz/does-not-exist.txt","mimeType":"text/plain","path":"./dynamic-tar-gz/does-not-exist.txt","lastModified":/* ts */1706742000000});
+registerFile("./dynamic-tar-gz/file.txt", {"name":"./dynamic-tar-gz/file.txt","mimeType":"text/plain","path":"./_file/dynamic-tar-gz/file.c93138d8.txt","lastModified":/* ts */1706742000000});
+registerFile("./dynamic-tar/does-not-exist.txt", {"name":"./dynamic-tar/does-not-exist.txt","mimeType":"text/plain","path":"./dynamic-tar/does-not-exist.txt","lastModified":/* ts */1706742000000});
+registerFile("./dynamic-tar/file.txt", {"name":"./dynamic-tar/file.txt","mimeType":"text/plain","path":"./_file/dynamic-tar/file.c93138d8.txt","lastModified":/* ts */1706742000000});
+registerFile("./static-tar/does-not-exist.txt", {"name":"./static-tar/does-not-exist.txt","mimeType":"text/plain","path":"./static-tar/does-not-exist.txt","lastModified":/* ts */1706742000000});
+registerFile("./static-tar/file.txt", {"name":"./static-tar/file.txt","mimeType":"text/plain","path":"./_file/static-tar/file.c93138d8.txt","lastModified":/* ts */1706742000000});
+registerFile("./static-tgz/file.txt", {"name":"./static-tgz/file.txt","mimeType":"text/plain","path":"./_file/static-tgz/file.c93138d8.txt","lastModified":/* ts */1706742000000});
 
 define({id: "d5134368", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
diff --git a/test/output/build/archives.posix/zip.html b/test/output/build/archives.posix/zip.html
index 930e3bf35..8ce30be01 100644
--- a/test/output/build/archives.posix/zip.html
+++ b/test/output/build/archives.posix/zip.html
@@ -15,10 +15,10 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./dynamic/file.txt", {"name":"./dynamic/file.txt","mimeType":"text/plain","path":"./_file/dynamic/file.c93138d8.txt"});
-registerFile("./dynamic/not-found.txt", {"name":"./dynamic/not-found.txt","mimeType":"text/plain","path":"./dynamic/not-found.txt"});
-registerFile("./static/file.txt", {"name":"./static/file.txt","mimeType":"text/plain","path":"./_file/static/file.d9014c46.txt"});
-registerFile("./static/not-found.txt", {"name":"./static/not-found.txt","mimeType":"text/plain","path":"./static/not-found.txt"});
+registerFile("./dynamic/file.txt", {"name":"./dynamic/file.txt","mimeType":"text/plain","path":"./_file/dynamic/file.c93138d8.txt","lastModified":/* ts */1706742000000});
+registerFile("./dynamic/not-found.txt", {"name":"./dynamic/not-found.txt","mimeType":"text/plain","path":"./dynamic/not-found.txt","lastModified":/* ts */1706742000000});
+registerFile("./static/file.txt", {"name":"./static/file.txt","mimeType":"text/plain","path":"./_file/static/file.d9014c46.txt","lastModified":/* ts */1706742000000});
+registerFile("./static/not-found.txt", {"name":"./static/not-found.txt","mimeType":"text/plain","path":"./static/not-found.txt","lastModified":/* ts */1706742000000});
 
 define({id: "d3b9d0ee", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
diff --git a/test/output/build/archives.win32/tar.html b/test/output/build/archives.win32/tar.html
index dd10bfdce..910eb3e19 100644
--- a/test/output/build/archives.win32/tar.html
+++ b/test/output/build/archives.win32/tar.html
@@ -15,9 +15,9 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./static-tar/does-not-exist.txt", {"name":"./static-tar/does-not-exist.txt","mimeType":"text/plain","path":"./static-tar/does-not-exist.txt"});
-registerFile("./static-tar/file.txt", {"name":"./static-tar/file.txt","mimeType":"text/plain","path":"./_file/static-tar/file.c93138d8.txt"});
-registerFile("./static-tgz/file.txt", {"name":"./static-tgz/file.txt","mimeType":"text/plain","path":"./_file/static-tgz/file.c93138d8.txt"});
+registerFile("./static-tar/does-not-exist.txt", {"name":"./static-tar/does-not-exist.txt","mimeType":"text/plain","path":"./static-tar/does-not-exist.txt","lastModified":/* ts */1706742000000});
+registerFile("./static-tar/file.txt", {"name":"./static-tar/file.txt","mimeType":"text/plain","path":"./_file/static-tar/file.c93138d8.txt","lastModified":/* ts */1706742000000});
+registerFile("./static-tgz/file.txt", {"name":"./static-tgz/file.txt","mimeType":"text/plain","path":"./_file/static-tgz/file.c93138d8.txt","lastModified":/* ts */1706742000000});
 
 define({id: "d5134368", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
diff --git a/test/output/build/archives.win32/zip.html b/test/output/build/archives.win32/zip.html
index 0ec065085..8c8e42d1c 100644
--- a/test/output/build/archives.win32/zip.html
+++ b/test/output/build/archives.win32/zip.html
@@ -15,8 +15,8 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./static/file.txt", {"name":"./static/file.txt","mimeType":"text/plain","path":"./_file/static/file.d9014c46.txt"});
-registerFile("./static/not-found.txt", {"name":"./static/not-found.txt","mimeType":"text/plain","path":"./static/not-found.txt"});
+registerFile("./static/file.txt", {"name":"./static/file.txt","mimeType":"text/plain","path":"./_file/static/file.d9014c46.txt","lastModified":/* ts */1706742000000});
+registerFile("./static/not-found.txt", {"name":"./static/not-found.txt","mimeType":"text/plain","path":"./static/not-found.txt","lastModified":/* ts */1706742000000});
 
 define({id: "d3b9d0ee", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
diff --git a/test/output/build/fetches/foo.html b/test/output/build/fetches/foo.html
index 380a14dcc..8ba373037 100644
--- a/test/output/build/fetches/foo.html
+++ b/test/output/build/fetches/foo.html
@@ -16,8 +16,8 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./foo/foo-data.csv", {"name":"./foo/foo-data.csv","mimeType":"text/csv","path":"./_file/foo/foo-data.24ef4634.csv"});
-registerFile("./foo/foo-data.json", {"name":"./foo/foo-data.json","mimeType":"application/json","path":"./_file/foo/foo-data.67358ed8.json"});
+registerFile("./foo/foo-data.csv", {"name":"./foo/foo-data.csv","mimeType":"text/csv","path":"./_file/foo/foo-data.24ef4634.csv","lastModified":/* ts */1706742000000});
+registerFile("./foo/foo-data.json", {"name":"./foo/foo-data.json","mimeType":"application/json","path":"./_file/foo/foo-data.67358ed8.json","lastModified":/* ts */1706742000000});
 
 define({id: "47a695da", inputs: ["display"], outputs: ["fooJsonData","fooCsvData"], body: async (display) => {
 const {fooJsonData, fooCsvData} = await import("./_import/foo/foo.6fd063d5.js");
diff --git a/test/output/build/fetches/top.html b/test/output/build/fetches/top.html
index 762624aa0..744f9f54a 100644
--- a/test/output/build/fetches/top.html
+++ b/test/output/build/fetches/top.html
@@ -17,10 +17,10 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./foo/foo-data.csv", {"name":"./foo/foo-data.csv","mimeType":"text/csv","path":"./_file/foo/foo-data.24ef4634.csv"});
-registerFile("./foo/foo-data.json", {"name":"./foo/foo-data.json","mimeType":"application/json","path":"./_file/foo/foo-data.67358ed8.json"});
-registerFile("./top-data.csv", {"name":"./top-data.csv","mimeType":"text/csv","path":"./_file/top-data.24ef4634.csv"});
-registerFile("./top-data.json", {"name":"./top-data.json","mimeType":"application/json","path":"./_file/top-data.67358ed8.json"});
+registerFile("./foo/foo-data.csv", {"name":"./foo/foo-data.csv","mimeType":"text/csv","path":"./_file/foo/foo-data.24ef4634.csv","lastModified":/* ts */1706742000000});
+registerFile("./foo/foo-data.json", {"name":"./foo/foo-data.json","mimeType":"application/json","path":"./_file/foo/foo-data.67358ed8.json","lastModified":/* ts */1706742000000});
+registerFile("./top-data.csv", {"name":"./top-data.csv","mimeType":"text/csv","path":"./_file/top-data.24ef4634.csv","lastModified":/* ts */1706742000000});
+registerFile("./top-data.json", {"name":"./top-data.json","mimeType":"application/json","path":"./_file/top-data.67358ed8.json","lastModified":/* ts */1706742000000});
 
 define({id: "cb908c08", inputs: ["display"], outputs: ["fooCsvData","fooJsonData","topCsvData","topJsonData"], body: async (display) => {
 const {fooCsvData, fooJsonData, topCsvData, topJsonData} = await import("./_import/top.d8f5cc36.js");
diff --git a/test/output/build/files/files.html b/test/output/build/files/files.html
index 52687befe..2ef6532da 100644
--- a/test/output/build/files/files.html
+++ b/test/output/build/files/files.html
@@ -15,9 +15,10 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./file-top.csv", {"name":"./file-top.csv","mimeType":"text/csv","path":"./_file/file-top.01a7ce0a.csv"});
-registerFile("./observable logo.png", {"name":"./observable logo.png","mimeType":"image/png","path":"./_file/observable logo.b620bd08.png"});
-registerFile("./subsection/file-sub.csv", {"name":"./subsection/file-sub.csv","mimeType":"text/csv","path":"./_file/subsection/file-sub.72c2c61c.csv"});
+registerFile("./file-top.csv", {"name":"./file-top.csv","mimeType":"text/csv","path":"./_file/file-top.01a7ce0a.csv","lastModified":/* ts */1706742000000});
+registerFile("./observable logo.png", {"name":"./observable logo.png","mimeType":"image/png","path":"./_file/observable logo.b620bd08.png","lastModified":/* ts */1706742000000});
+registerFile("./subsection/file-sub.csv", {"name":"./subsection/file-sub.csv","mimeType":"text/csv","path":"./_file/subsection/file-sub.72c2c61c.csv","lastModified":/* ts */1706742000000});
+registerFile("./unknown-mime-extension.really", {"name":"./unknown-mime-extension.really","path":"./unknown-mime-extension.really"});
 
 define({id: "10037545", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
@@ -37,6 +38,12 @@
 ))
 }});
 
+define({id: "cee3ab67", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
+display(await(
+FileAttachment("unknown-mime-extension.really")
+))
+}});
+
 </script>
 <input id="observablehq-sidebar-toggle" type="checkbox" title="Toggle sidebar">
 <label id="observablehq-sidebar-backdrop" for="observablehq-sidebar-toggle"></label>
@@ -63,6 +70,7 @@
 <div id="cell-10037545" class="observablehq observablehq--block observablehq--loading"></div>
 <div id="cell-453a8147" class="observablehq observablehq--block observablehq--loading"></div>
 <div id="cell-444c421e" class="observablehq observablehq--block observablehq--loading"></div>
+<div id="cell-cee3ab67" class="observablehq observablehq--block observablehq--loading"></div>
 <p><img src="./_file/observable logo small.8a915536.png" alt=""></p>
 </main>
 <footer id="observablehq-footer">
diff --git a/test/output/build/files/subsection/subfiles.html b/test/output/build/files/subsection/subfiles.html
index 7b53e9062..8170662ae 100644
--- a/test/output/build/files/subsection/subfiles.html
+++ b/test/output/build/files/subsection/subfiles.html
@@ -15,8 +15,8 @@
 import {define} from "../_observablehq/client.js";
 import {registerFile} from "../_observablehq/stdlib.js";
 
-registerFile("../file-top.csv", {"name":"../file-top.csv","mimeType":"text/csv","path":"../_file/file-top.01a7ce0a.csv"});
-registerFile("./file-sub.csv", {"name":"./file-sub.csv","mimeType":"text/csv","path":"../_file/subsection/file-sub.72c2c61c.csv"});
+registerFile("../file-top.csv", {"name":"../file-top.csv","mimeType":"text/csv","path":"../_file/file-top.01a7ce0a.csv","lastModified":/* ts */1706742000000});
+registerFile("./file-sub.csv", {"name":"./file-sub.csv","mimeType":"text/csv","path":"../_file/subsection/file-sub.72c2c61c.csv","lastModified":/* ts */1706742000000});
 
 define({id: "ef9a31ef", inputs: ["FileAttachment","display"], body: async (FileAttachment,display) => {
 display(await(
diff --git a/test/output/build/imports/foo/foo.html b/test/output/build/imports/foo/foo.html
index 8c3935a1c..a6ff8013d 100644
--- a/test/output/build/imports/foo/foo.html
+++ b/test/output/build/imports/foo/foo.html
@@ -21,7 +21,7 @@
 import {define} from "../_observablehq/client.js";
 import {registerFile} from "../_observablehq/stdlib.js";
 
-registerFile("../top.js", {"name":"../top.js","mimeType":"text/javascript","path":"../_file/top.a53c5d5b.js"});
+registerFile("../top.js", {"name":"../top.js","mimeType":"text/javascript","path":"../_file/top.a53c5d5b.js","lastModified":/* ts */1706742000000});
 
 define({id: "261e010e", inputs: ["display","FileAttachment"], outputs: ["d3","bar","top"], body: async (display,FileAttachment) => {
 const [d3, {bar}, {top}] = await Promise.all([import("../_npm/d3@7.8.5/_esm.js"), import("../_import/bar/bar.13bb8056.js"), import("../_import/top.160847a6.js")]);
diff --git a/test/output/build/multi/index.html b/test/output/build/multi/index.html
index 608445594..64b13c4e1 100644
--- a/test/output/build/multi/index.html
+++ b/test/output/build/multi/index.html
@@ -16,8 +16,8 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./file1.csv", {"name":"./file1.csv","mimeType":"text/csv","path":"./_file/file1.259f3fd9.csv"});
-registerFile("./file2.csv", {"name":"./file2.csv","mimeType":"text/csv","path":"./_file/file2.c70f7d51.csv"});
+registerFile("./file1.csv", {"name":"./file1.csv","mimeType":"text/csv","path":"./_file/file1.259f3fd9.csv","lastModified":/* ts */1706742000000});
+registerFile("./file2.csv", {"name":"./file2.csv","mimeType":"text/csv","path":"./_file/file2.c70f7d51.csv","lastModified":/* ts */1706742000000});
 
 define({id: "1bcb5df5", inputs: ["FileAttachment"], outputs: ["f1"], body: (FileAttachment) => {
 const f1 = FileAttachment("file1.csv").csv();
diff --git a/test/output/build/simple/simple.html b/test/output/build/simple/simple.html
index da71f68fe..520cc47e3 100644
--- a/test/output/build/simple/simple.html
+++ b/test/output/build/simple/simple.html
@@ -15,7 +15,7 @@
 import {define} from "./_observablehq/client.js";
 import {registerFile} from "./_observablehq/stdlib.js";
 
-registerFile("./data.txt", {"name":"./data.txt","mimeType":"text/plain","path":"./_file/data.9d63c3b5.txt"});
+registerFile("./data.txt", {"name":"./data.txt","mimeType":"text/plain","path":"./_file/data.9d63c3b5.txt","lastModified":/* ts */1706742000000});
 
 define({id: "115586ff", inputs: ["FileAttachment"], outputs: ["result"], body: (FileAttachment) => {
 let result = FileAttachment("data.txt").text();