capsite/webapp: postForm, a multipart POST that can echo a cookie into a field

Some sites check a double-submit token: the session value sent as a
cookie and again in the form body. postForm(fields, echoCookies) builds
a multipart body and copies the named cookies (from the header store,
at send time) into fields, so the caller never sees the value.

It returns a Reply instead of throwing on non-OK: status, content type,
content-disposition, the redirect location with its query stripped, and
the body as bytes (the caller decodes, e.g. per a charset the body
declares). Redirects are not followed, so an expired session shows up
as a 3xx. Set-Cookie is not passed back. Errors name keys, never values.

Generated-by: Claude Opus 5.5

capsite-checklist.md

@@ -109,10 +109,11 @@ narrative.
               weekly page renders against prod.
   - [ ] **6. Cookie expiry**: when diigo's session ends, head refreshes
         fail; the public page keeps serving what's stored (say so on the
-        page, don't fail silently). Rotation is manual: re-mint via
+        page, don't fail silently). Rotation is in place, keeping the
-        `/_connect`. Open question: can an existing cache be re-wired to
+        webapp id (so the cache's wiring and ids hold), by the store id
-        a new webapp id (keeping its cache id and public username), or
+        minted alongside it and kept by the account owner: `PUT
-        does re-mint mean a new cache? Prefer re-wire — durable ids.
+        /store/<storeId>/cookie` (webapp README, "The header store").
+        Still open: a rotate form in diigo-cache's UI.
   - [ ] **7. bib sync #195**: repeat the pattern for the next
         read-access need (webapp mints for any origin; the cache's
         item shape is diigo-specific): [the zotero goal tree](zotero-checklist.md).

diigo-cache/src/index.ts

@@ -174,11 +174,13 @@ async function proxyMint(request: Request, env: Env): Promise<Response> {
 			const detail = (await res.text()).slice(0, 200);
 			return home(env, { error: `mint said ${res.status}: ${detail}` }, null);
 		}
-		// webapp answers {id} (+ x-webapp-id); the id rides the header, the
+		// webapp answers {id, storeId} (+ x-webapp-id, x-webapp-store-id);
-		// wire page is ours
+		// the ids ride the headers, the wire page is ours
 		const id = res.headers.get("x-webapp-id");
 		if (!id) return home(env, { error: "mint produced no id" }, null);
-		return await wirePage(id);
+		const storeId = res.headers.get("x-webapp-store-id");
+		if (!storeId) console.warn({ event: "mint", outcome: "no store id: this session cannot be rotated" });
+		return await wirePage(id, storeId);
 	} catch (err) {
 		console.error({ event: "mint", error: String(err) });
 		return home(env, { error: `mint failed: ${String(err)}` }, null);
@@ -188,22 +190,37 @@ async function proxyMint(request: Request, env: Env): Promise<Response> {
 /** the credential-save helper, once per page (see ./pm-save.ts) */
 const PM_SAVE_JS = pmSave.toString();
 
-/** the suggested petname gets the holder's local hh:mm (the worker only
+/** the suggested petname (in the input with id `petnameId`) gets the
- * knows UTC), so two saves the same day are told apart at a glance */
+ * holder's local hh:mm (the worker only knows UTC), so two saves the same
-const PETNAME_TIME_JS = `{
+ * day are told apart at a glance */
-	const p = document.getElementById("petname");
+function petnameTimeJs(petnameId: string): string {
+	return `{
+	const p = document.getElementById(${JSON.stringify(petnameId)});
 	const d = new Date();
 	p.value += " " + String(d.getHours()).padStart(2, "0") + ":" + String(d.getMinutes()).padStart(2, "0");
 }`;
-
-/** the onclick that hands pmSave its browser powers */
-function pmSaveClick(value: string): string {
-	return `pmSave(this, ${JSON.stringify(value)}, { petname: document.getElementById("petname"), credentials: navigator.credentials, PasswordCredential: window.PasswordCredential, log: console })`;
 }
 
-/** the wire step, with the freshly-minted webapp id pre-filled */
+/** the onclick that hands pmSave its browser powers, saving under the
-async function wirePage(webappId: string): Promise<Response> {
+ * petname in the input with id `petnameId` */
+function pmSaveClick(value: string, petnameId: string): string {
+	return `pmSave(this, ${JSON.stringify(value)}, { petname: document.getElementById(${JSON.stringify(petnameId)}), credentials: navigator.credentials, PasswordCredential: window.PasswordCredential, log: console })`;
+}
+
+/** the wire step, with the freshly-minted webapp id pre-filled, and the
+ * store id (rotating the cookie) for the account owner to keep */
+async function wirePage(webappId: string, storeId: string | null): Promise<Response> {
 	const fingerprint = await nick(webappId);
+	const storeSection = storeId
+		? `<h2>keep: the cookie's store id</h2>
+<p>This one is yours alone, not the cache's: with it you can rotate the
+diigo session (log in again, paste the new cookie) or revoke it. Fingerprint
+<code>${esc(await nick(storeId))}</code>
+<button type="button" onclick='navigator.clipboard.writeText(${JSON.stringify(storeId)}).then(() => this.textContent = "copied ✓")'>copy</button></p>
+<p><label>your petname for it <input id="store-petname" autocomplete="off" size="30" value="${esc(`diigo cookie store ${await nick(storeId)}`)}"></label></p>
+<script>${petnameTimeJs("store-petname")}</script>
+<p><button type="button" onclick='${pmSaveClick(storeId, "store-petname")}'>save to password manager</button></p>`
+		: `<p><b>note:</b> webapp sent no store id, so this session's cookie cannot be rotated; when it expires, mint again.</p>`;
 	const body = `<!doctype html>
 <html><head><meta charset="utf-8"><title>diigo cache: step 2 — wire the cache</title></head>
 <body>
@@ -212,8 +229,10 @@ async function wirePage(webappId: string): Promise<Response> {
 <button type="button" onclick='navigator.clipboard.writeText(${JSON.stringify(webappId)}).then(() => this.textContent = "copied ✓")'>copy</button></p>
 <p><label>your petname for it <input id="petname" autocomplete="off" size="30" value="${esc(`diigo webapp ${fingerprint}`)}"></label>
 <small>(private to you: the password-manager username; never sent to the server)</small></p>
-<script>${PETNAME_TIME_JS}</script>
+<script>${petnameTimeJs("petname")}</script>
-<p><button type="button" onclick='${pmSaveClick(webappId)}'>save to password manager</button></p>
+<p><button type="button" onclick='${pmSaveClick(webappId, "petname")}'>save to password manager</button></p>
+${storeSection}
+<h2>wire</h2>
 <p>choose the cache mode, then <b>wire</b> — the next page shows the
 <b>cache id</b> (copy that too), after which you land back on home:</p>
 <form method="post" action="/_wire">
@@ -320,8 +339,8 @@ async function wiredPage(cacheId: string, note: string, hasPublic: boolean): Pro
 <button type="button" onclick='navigator.clipboard.writeText(${JSON.stringify(cacheId)}).then(() => this.textContent = "copied ✓")'>copy</button></p>
 <p><label>your petname for it <input id="petname" autocomplete="off" size="30" value="${esc(`diigo cache ${fingerprint}`)}"></label>
 <small>(private to you: the password-manager username; never sent to the server)</small></p>
-<script>${PETNAME_TIME_JS}</script>
+<script>${petnameTimeJs("petname")}</script>
-<p><button type="button" onclick='${pmSaveClick(cacheId)}'>save to password manager</button></p>
+<p><button type="button" onclick='${pmSaveClick(cacheId, "petname")}'>save to password manager</button></p>
 <p>${note}</p>
 <p><a href="/cache/#${esc(cacheId)}">open this cache</a> — its <b>webkey</b>
 (bookmark it, or save the id above): fill it, watch progress${hasPublic ? ", fill its public companion" : ""}.</p>

docs/cookie-rotation-wiring.html

@@ -0,0 +1,146 @@
+<!doctype html>
+<html><head><meta charset="utf-8">
+<title>webapp cookie rotation: who holds what</title>
+<!-- drawn after the style of MarkM's ERTP slides; cookie-rotation-wiring.png is a headless-Chromium screenshot of this page -->
+<style>
+  html, body { margin: 0; background: #fff; }
+  .sans { font-family: "Helvetica Neue", "DejaVu Sans", sans-serif; }
+  .obj { font-family: "DejaVu Serif", serif; font-style: italic; }
+  .mono { font-family: "DejaVu Sans Mono", monospace; }
+</style></head>
+<body>
+<svg id="c" xmlns="http://www.w3.org/2000/svg" width="1120" height="820" viewBox="0 0 1120 820"
+  role="img" aria-labelledby="title desc">
+  <title id="title">webapp cookie rotation: who holds what</title>
+  <desc id="desc">Three actors and two makers. Alice holds a reference to a store made by
+makeMapStore, and to diigo-cache, which she wired up. She rotates the cookie
+by saying: await E(store).set("cookie", freshCookie). The store, and its
+read-only facets, both refer to the store's kv table, whose one row maps
+"cookie" to the session; its shapes are keyShape "cookie" and valueShape
+M.string(). makeWebApp makes access objects; each refers to its init
+table: url, headers, and headerStore. headerStore refers to the store's
+read-only facet, which access reads at every send. diigo-cache holds a
+reference to access. Mallory, who learned the instance id, also holds a
+reference to access, so she can use the cookie, but she has no reference
+to the store, so she cannot rotate it or swap in her own session.</desc>
+  <defs>
+    <radialGradient id="ball" cx="40%" cy="35%" r="70%">
+      <stop offset="0%" stop-color="#7cc8f8"/>
+      <stop offset="100%" stop-color="#3aa6ee"/>
+    </radialGradient>
+    <linearGradient id="objfill" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0%" stop-color="#6cbcf4"/>
+      <stop offset="100%" stop-color="#4aa8ec"/>
+    </linearGradient>
+    <marker id="head" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="9" markerHeight="9" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#1d4f7a"/>
+    </marker>
+  </defs>
+</svg>
+<script>
+const svg = document.getElementById("c");
+const NS = "http://www.w3.org/2000/svg";
+const el = (name, attrs, parent = svg) => {
+  const e = document.createElementNS(NS, name);
+  for (const [k, v] of Object.entries(attrs)) e.setAttribute(k, v);
+  parent.appendChild(e);
+  return e;
+};
+const text = (x, y, s, cls, attrs = {}) => {
+  const t = el("text", { x, y, class: cls, "text-anchor": "middle", fill: "#1d3550", ...attrs });
+  t.textContent = s;
+  return t;
+};
+
+const INK = "#1d4f7a";
+const dot = (x, y) => el("circle", { cx: x, cy: y, r: 4.5, fill: INK });
+/** a reference: dot at the holder, arrowhead at the target */
+const ref = (x1, y1, x2, y2, bend = 0, extra = {}) => {
+  dot(x1, y1);
+  const mx = (x1 + x2) / 2 - (y2 - y1) * bend, my = (y1 + y2) / 2 + (x2 - x1) * bend;
+  el("path", { d: `M${x1},${y1} Q${mx},${my} ${x2},${y2}`, fill: "none", stroke: INK, "stroke-width": 2, "marker-end": "url(#head)", ...extra });
+};
+
+// maker box: a pale rounded region, with stacked instances inside
+function maker(x, y, w, h, label) {
+  el("rect", { x, y, width: w, height: h, rx: 26, fill: "#d6ecfb", stroke: "#b5dbf5", "stroke-width": 1.5 });
+  text(x + 18, y + 30, label, "obj", { "text-anchor": "start", "font-size": 20 });
+  for (let i = 2; i >= 0; i -= 1) {
+    el("rect", {
+      x: x + 18 + i * 9, y: y + 48 + i * 9, width: w - 52, height: h - 82, rx: 22,
+      fill: "#c8e5fa", stroke: "#8ec9f2", "stroke-width": 1.5, "fill-opacity": 0.9,
+    });
+  }
+}
+// an object: rounded square, optionally stacked (several made)
+function obj(x, y, w, h, label, stacked = false) {
+  const n = stacked ? 3 : 1;
+  for (let i = n - 1; i >= 0; i -= 1) {
+    el("rect", { x: x + i * 7, y: y - i * 7, width: w, height: h, rx: 12, fill: "url(#objfill)", stroke: "#2f8fd6", "stroke-width": 1.5 });
+  }
+  text(x + w / 2, y + h / 2 + 7, label, "obj", { "font-size": 19 });
+}
+function actor(cx, cy, label) {
+  el("circle", { cx, cy, r: 52, fill: "url(#ball)", stroke: "#2f8fd6", "stroke-width": 1.5 });
+  text(cx, cy + 6, label, "sans", { "font-size": label.length > 8 ? 15 : 17 });
+}
+// a table like the ERTP ledger
+function table(x, y, title, rows, colW) {
+  const rowH = 28, w = colW[0] + colW[1];
+  el("rect", { x, y, width: w, height: 36 + rowH * rows.length, fill: "#5fb5f2", stroke: "#2f8fd6", "stroke-width": 1.5 });
+  text(x + w / 2, y + 25, title, "obj", { "font-size": 18 });
+  rows.forEach(([k, v], i) => {
+    const ry = y + 36 + i * rowH;
+    el("line", { x1: x, y1: ry, x2: x + w, y2: ry, stroke: "#2f8fd6", "stroke-width": 1.2 });
+    text(x + 10, ry + 19, k, "mono", { "text-anchor": "start", "font-size": 14 });
+    if (v) text(x + colW[0] + 10, ry + 19, v, "mono", { "text-anchor": "start", "font-size": 14 });
+  });
+  el("line", { x1: x + colW[0], y1: y + 36, x2: x + colW[0], y2: y + 36 + rowH * rows.length, stroke: "#1d4f7a", "stroke-width": 1.5 });
+  return { rowY: (i) => y + 36 + i * rowH + rowH / 2, x, w, colX: x + colW[0] };
+}
+
+// speech bubble (Alice rotates after logging in again)
+el("path", {
+  d: "M30,22 h470 a16,16 0 0 1 16,16 v34 a16,16 0 0 1 -16,16 h-330 l-38,48 l6,-48 h-102 a16,16 0 0 1 -16,-16 v-34 a16,16 0 0 1 16,-16 z",
+  fill: "#d9d9d9", stroke: "#555", "stroke-width": 2,
+});
+const code = el("text", { x: 46, y: 62, class: "mono", "font-size": 17, fill: "#222" });
+code.innerHTML = '<tspan fill="#b0177b">await</tspan> E(store).set(<tspan fill="#1a7f37">"cookie"</tspan>, freshCookie);';
+
+// actors
+actor(150, 200, "Alice");
+actor(560, 200, "diigo-cache");
+actor(930, 200, "Mallory");
+
+// makers
+maker(30, 320, 470, 470, "makeMapStore");
+maker(560, 320, 530, 470, "makeWebApp");
+
+// MapStoreDo insides
+obj(80, 420, 120, 80, "store");
+obj(80, 600, 120, 80, "readOnly", true);
+const kv = table(260, 430, "kv", [["cookie", "session=…"], ["", ""], ["", ""], ["", ""], ["", ""]], [90, 110]);
+
+// WebAppDo insides
+obj(620, 560, 140, 90, "access", true);
+const init = table(830, 420, "init", [["url", "diigo…"], ["headers", "{…}"], ["headerStore", ""], ["", ""]], [130, 85]);
+
+// references
+ref(140, 228, 125, 418, 0.05); // Alice → store
+ref(172, 224, 508, 210, 0.04); // Alice → diigo-cache (she wired it)
+ref(560 - 6, 200 + 18, 660, 553, 0.12); // cache → access
+ref(930 - 14, 200 + 20, 720, 553, -0.08); // Mallory → access
+ref(160, 470, kv.x - 2, kv.rowY(0), 0.05); // store → kv
+ref(150, 666, kv.x - 2, kv.rowY(0) + 6, -0.25); // readOnly → kv (read)
+ref(760, 600, init.x - 2, init.rowY(2), -0.1); // access → init
+ref(init.colX + 40, init.rowY(2), 208, 640, -0.28); // headerStore → readOnly
+
+// captions
+const cap = (x, y, s, attrs = {}) => text(x, y, s, "sans", { "font-size": 14, fill: "#33536f", ...attrs });
+cap(930, 118, "holds the instance id:", {});
+cap(930, 136, "uses the cookie, can't reach store", {});
+cap(330, 300, "storeId: rotate · revoke", {});
+cap(760, 806, "init.headerStore → the store's read-only facet, read at every send", {});
+cap(265, 806, "shapes: keyShape \"cookie\", valueShape M.string()", {});
+</script>
+</body></html>

lib/package.json

@@ -0,0 +1,16 @@
+{
+	"name": "capsite-lib",
+	"private": true,
+	"type": "module",
+	"scripts": {
+		"types": "wrangler types -c wrangler.tests.jsonc",
+		"lint": "wrangler types -c wrangler.tests.jsonc --check && tsc -p tsconfig.json && tsc -p tests/tsconfig.json",
+		"test": "vitest run"
+	},
+	"devDependencies": {
+		"@cloudflare/vitest-plugin": "1.3.6",
+		"typescript": "^5.9.0",
+		"vitest": "4.1.11",
+		"wrangler": "^4.148.0"
+	}
+}

lib/src/patterns.ts

@@ -0,0 +1,129 @@
+/**
+ * @file a work-alike for enough of @endo/patterns: `M.string()`, `M.any()`,
+ * and literal patterns (a string, number, boolean, or null matches only
+ * itself, so `"cookie"` as a key shape admits exactly one key). Matchers
+ * are the same data endo makes: tagged records, as from @endo/pass-style's
+ * `makeTagged` (frozen here, where endo would harden).
+ *
+ * Structured clone (DO storage, Workers RPC) drops a tagged record's
+ * symbol-keyed and non-enumerable properties, so patterns cross those
+ * boundaries in endo's smallcaps encoding: see {@link toSmallcaps}.
+ * @see https://github.com/endojs/endo/tree/master/packages/patterns
+ * @see https://github.com/endojs/endo/blob/master/packages/marshal/src/encodeToSmallcaps.js
+ */
+
+const PASS_STYLE = Symbol.for("passStyle");
+
+export type Tagged = Readonly<{ [Symbol.toStringTag]: string; payload: unknown }>;
+export type Pattern = Tagged | string | number | boolean | null;
+
+/** @endo/pass-style's `makeTagged` */
+export function makeTagged(tag: string, payload: unknown): Tagged {
+	return Object.freeze(
+		Object.create(Object.prototype, {
+			[PASS_STYLE]: { value: "tagged" },
+			[Symbol.toStringTag]: { value: tag },
+			payload: { value: payload, enumerable: true },
+		}),
+	) as Tagged;
+}
+
+const isTagged = (x: unknown): x is Tagged =>
+	typeof x === "object" && x !== null && (x as Record<symbol, unknown>)[PASS_STYLE] === "tagged";
+
+const StringShape = makeTagged("match:string", Object.freeze([]));
+const AnyShape = makeTagged("match:any", undefined);
+
+export const M = Object.freeze({
+	string: (): Tagged => StringShape,
+	any: (): Tagged => AnyShape,
+});
+
+export function matches(specimen: unknown, pattern: Pattern): boolean {
+	if (typeof pattern === "object" && pattern !== null) {
+		const tag = isTagged(pattern) ? pattern[Symbol.toStringTag] : undefined;
+		switch (tag) {
+			case "match:string":
+				return typeof specimen === "string";
+			case "match:any":
+				return true;
+			default:
+				throw new TypeError("not a pattern");
+		}
+	}
+	return Object.is(specimen, pattern);
+}
+
+/** the pattern as written in code, e.g. `M.string()` or `"cookie"` */
+export function describe(pattern: Pattern): string {
+	if (typeof pattern === "object" && pattern !== null) {
+		return `M.${pattern[Symbol.toStringTag].replace(/^match:/, "")}()`;
+	}
+	return JSON.stringify(pattern);
+}
+
+/**
+ * throw unless `specimen` matches `pattern`. Unlike endo's, the message
+ * names the pattern and `label` but never the specimen: specimens here
+ * can be credentials, and messages cross RPC and land in logs.
+ */
+export function mustMatch(specimen: unknown, pattern: Pattern, label: string): void {
+	if (!matches(specimen, pattern)) {
+		throw new TypeError(`${label}: must match ${describe(pattern)}`);
+	}
+}
+
+/** a smallcaps-encoded passable, as JSON-able data */
+export type Smallcaps = null | boolean | number | string | Smallcaps[] | { "#tag": string; payload: Smallcaps };
+
+/** smallcaps quotes strings that start with one of these with `!` */
+const startsSpecial = (s: string) => /^[!-\-]/.test(s);
+
+/**
+ * the subset of @endo/marshal's smallcaps encoding that patterns here use:
+ * primitives, arrays, and tagged records (not a whole CapData: no `#`
+ * body prefix, no slots)
+ */
+export function toSmallcaps(passable: unknown): Smallcaps {
+	if (passable === undefined) return "#undefined";
+	if (passable === null || typeof passable === "boolean") return passable;
+	if (typeof passable === "number") {
+		if (Number.isNaN(passable)) return "#NaN";
+		if (passable === Infinity) return "#Infinity";
+		if (passable === -Infinity) return "#-Infinity";
+		return Object.is(passable, -0) ? 0 : passable;
+	}
+	if (typeof passable === "string") return startsSpecial(passable) ? `!${passable}` : passable;
+	if (Array.isArray(passable)) return passable.map(toSmallcaps);
+	if (isTagged(passable)) {
+		return { "#tag": toSmallcaps(passable[Symbol.toStringTag]) as string, payload: toSmallcaps(passable.payload) };
+	}
+	throw new TypeError("toSmallcaps: unsupported passable");
+}
+
+/** the inverse of {@link toSmallcaps} */
+export function fromSmallcaps(encoding: Smallcaps): unknown {
+	if (encoding === null || typeof encoding === "boolean" || typeof encoding === "number") return encoding;
+	if (typeof encoding === "string") {
+		if (encoding.startsWith("!")) return encoding.slice(1);
+		switch (encoding) {
+			case "#undefined":
+				return undefined;
+			case "#NaN":
+				return NaN;
+			case "#Infinity":
+				return Infinity;
+			case "#-Infinity":
+				return -Infinity;
+		}
+		if (startsSpecial(encoding)) throw new TypeError("fromSmallcaps: unsupported special string");
+		return encoding;
+	}
+	if (Array.isArray(encoding)) return Object.freeze(encoding.map(fromSmallcaps));
+	if (typeof encoding === "object" && "#tag" in encoding) {
+		const { "#tag": tag, payload, ...rest } = encoding;
+		if (Object.keys(rest).length > 0) throw new TypeError("fromSmallcaps: extra properties on a tagged record");
+		return makeTagged(fromSmallcaps(tag) as string, fromSmallcaps(payload));
+	}
+	throw new TypeError("fromSmallcaps: unsupported encoding");
+}

lib/src/store-do.ts

@@ -0,0 +1,60 @@
+/**
+ * @file a MapStore as a Durable Object of its own, so a store can be held
+ * apart from whoever reads it: the DO id is the store's full authority
+ * (e.g. the account owner's, to rotate a credential), while a reader is
+ * handed only {@link MapStoreDo.readOnly}.
+ */
+
+import { DurableObject } from "cloudflare:workers";
+import { fromSmallcaps, matches, toSmallcaps, type Pattern, type Smallcaps } from "./patterns.js";
+import { makeMapStore, type MapStore, type ReadonlyMapStore, type StoreShapes } from "./store.js";
+
+/** store shapes as they cross RPC and sit in storage: smallcaps-encoded
+ * (structured clone would strip a matcher down to its payload) */
+export type EncodedShapes = { keyShape?: Smallcaps; valueShape?: Smallcaps };
+
+export const encodeShapes = ({ keyShape, valueShape }: StoreShapes): EncodedShapes => ({
+	...(keyShape === undefined ? {} : { keyShape: toSmallcaps(keyShape) }),
+	...(valueShape === undefined ? {} : { valueShape: toSmallcaps(valueShape) }),
+});
+
+const decodeShapes = ({ keyShape, valueShape }: EncodedShapes): StoreShapes => ({
+	...(keyShape === undefined ? {} : { keyShape: fromSmallcaps(keyShape) as Pattern }),
+	...(valueShape === undefined ? {} : { valueShape: fromSmallcaps(valueShape) as Pattern }),
+});
+
+type Config = { label: string; shapes: EncodedShapes };
+
+/** a store whose label and shapes its creator fixes, once */
+export class MapStoreDo extends DurableObject {
+	/** one-shot: fix the label and shapes (see {@link encodeShapes}); an
+	 * identical re-configure is a no-op */
+	configure(label: string, shapes: EncodedShapes): void {
+		const decoded = decodeShapes(shapes);
+		for (const shape of [decoded.keyShape, decoded.valueShape]) {
+			if (shape !== undefined) matches(undefined, shape); // throws on a non-pattern
+		}
+		makeMapStore(label, decoded, this.ctx.storage.kv); // throws on a bad label
+		const config: Config = { label, shapes: encodeShapes(decoded) };
+		const existing = this.ctx.storage.kv.get<Config>("config");
+		if (existing) {
+			if (JSON.stringify(existing) !== JSON.stringify(config)) {
+				throw new Error("already configured with a different label or shapes");
+			}
+			return;
+		}
+		this.ctx.storage.kv.put("config", config);
+	}
+
+	/** the store, with full authority */
+	store(): MapStore<unknown> {
+		const config = this.ctx.storage.kv.get<Config>("config");
+		if (!config) throw new Error("not configured: this store was never set up");
+		return makeMapStore(config.label, decodeShapes(config.shapes), this.ctx.storage.kv);
+	}
+
+	/** the store's queries alone */
+	readOnly(): ReadonlyMapStore<unknown> {
+		return this.store().readOnly();
+	}
+}

lib/src/store.ts

@@ -0,0 +1,133 @@
+/**
+ * @file a work-alike for enough of @agoric/store's MapStore: string keys,
+ * shapes checked with ./patterns.js, entries kept in a Durable Object's
+ * synchronous KV storage. The facets are RpcTargets (workerd's / capnweb's,
+ * in place of endo's `Far`), so a store or its read-only view can be
+ * handed out by reference.
+ * @see https://github.com/Agoric/agoric-sdk/tree/master/packages/store
+ */
+
+import { RpcTarget } from "cloudflare:workers";
+import { M, mustMatch, type Pattern } from "./patterns.js";
+
+/** the storage a store needs: a DO's `ctx.storage.kv`, or a stand-in */
+export type Kv = Pick<SyncKvStorage, "get" | "put" | "delete" | "list">;
+
+export type StoreShapes = { keyShape?: Pattern; valueShape?: Pattern };
+
+/**
+ * Entries live under `store:<label>:<key>`, so the label also names the
+ * storage area (as a baggage key does for endo's durable stores): two
+ * stores with one label on one Kv are the same store.
+ *
+ * Error messages name the label and shapes, never keys or values.
+ */
+export function makeMapStore<V>(label: string, { keyShape = M.string(), valueShape = M.any() }: StoreShapes, kv: Kv) {
+	if (label.includes(":")) throw new TypeError("store label must not contain ':'");
+	const prefix = `store:${label}:`;
+	const core: Core<V> = {
+		label,
+		has: (key) => kv.get(prefix + key) !== undefined,
+		get: (key) => kv.get<V>(prefix + key),
+		put: (key, value) => kv.put(prefix + key, value),
+		delete: (key) => {
+			kv.delete(prefix + key);
+		},
+		entries: () => [...kv.list<V>({ prefix })].map(([k, v]): [string, V] => [k.slice(prefix.length), v]),
+		checkKey: (key) => mustMatch(key, keyShape, `${label}: key`),
+		checkValue: (value) => mustMatch(value, valueShape, `${label}: value`),
+	};
+	return new MapStore<V>(core);
+}
+
+type Core<V> = {
+	label: string;
+	has(key: string): boolean;
+	get(key: string): V | undefined;
+	put(key: string, value: V): void;
+	delete(key: string): void;
+	entries(): [string, V][];
+	checkKey(key: unknown): void;
+	checkValue(value: unknown): void;
+};
+
+/** the queries */
+function reads<V>(core: Core<V>) {
+	return {
+		has: (key: string): boolean => core.has(key),
+		get: (key: string): V => {
+			const value = core.get(key);
+			if (value === undefined) throw new RangeError(`${core.label}: key not found`);
+			return value;
+		},
+		keys: (): string[] => core.entries().map(([k]) => k),
+		values: (): V[] => core.entries().map(([, v]) => v),
+		entries: (): [string, V][] => core.entries(),
+		getSize: (): number => core.entries().length,
+	};
+}
+
+/** a store's queries only: what a reader of a rotating credential holds */
+export class ReadonlyMapStore<V> extends RpcTarget {
+	#reads: ReturnType<typeof reads<V>>;
+
+	constructor(core: Core<V>) {
+		super();
+		this.#reads = reads(core);
+	}
+
+	has(key: string): boolean {
+		return this.#reads.has(key);
+	}
+	get(key: string): V {
+		return this.#reads.get(key);
+	}
+	keys(): string[] {
+		return this.#reads.keys();
+	}
+	values(): V[] {
+		return this.#reads.values();
+	}
+	entries(): [string, V][] {
+		return this.#reads.entries();
+	}
+	getSize(): number {
+		return this.#reads.getSize();
+	}
+}
+
+/** a store's full authority: the queries plus `init`/`set`/`delete`, and
+ * {@link MapStore.readOnly} to hand out the queries alone */
+export class MapStore<V> extends ReadonlyMapStore<V> {
+	#core: Core<V>;
+
+	constructor(core: Core<V>) {
+		super(core);
+		this.#core = core;
+	}
+
+	/** add a key that is not yet present */
+	init(key: string, value: V): void {
+		this.#core.checkKey(key);
+		this.#core.checkValue(value);
+		if (this.#core.has(key)) throw new RangeError(`${this.#core.label}: key already registered`);
+		this.#core.put(key, value);
+	}
+
+	/** replace the value of a key that is present */
+	set(key: string, value: V): void {
+		this.#core.checkKey(key);
+		this.#core.checkValue(value);
+		if (!this.#core.has(key)) throw new RangeError(`${this.#core.label}: key not found`);
+		this.#core.put(key, value);
+	}
+
+	delete(key: string): void {
+		if (!this.#core.has(key)) throw new RangeError(`${this.#core.label}: key not found`);
+		this.#core.delete(key);
+	}
+
+	readOnly(): ReadonlyMapStore<V> {
+		return new ReadonlyMapStore(this.#core);
+	}
+}

lib/tests/store.test.ts

@@ -0,0 +1,142 @@
+import { env } from "cloudflare:workers";
+import { evictDurableObject } from "cloudflare:test";
+import { describe, expect, it } from "vitest";
+import { M, fromSmallcaps, makeTagged, matches, mustMatch, toSmallcaps } from "../src/patterns.js";
+import { encodeShapes } from "../src/store-do.js";
+
+type TestEnv = {
+	STORE_DO: DurableObjectNamespace<import("./test-worker.js").StoreHost>;
+	MAP_STORE_DO: DurableObjectNamespace<import("../src/store-do.js").MapStoreDo>;
+};
+const testEnv = env as unknown as TestEnv;
+
+const SECRET = "session=s3kr1t";
+
+/** the message an RPC call fails with, or "" if it succeeds */
+async function errorOf(call: Promise<unknown>): Promise<string> {
+	try {
+		await call;
+		return "";
+	} catch (err) {
+		return String(err);
+	}
+}
+
+describe("patterns", () => {
+	it("M.string() matches strings only; a literal matches only itself", () => {
+		expect(matches("x", M.string())).toBe(true);
+		expect(matches(1, M.string())).toBe(false);
+		expect(matches(undefined, M.any())).toBe(true);
+		expect(matches("cookie", "cookie")).toBe(true);
+		expect(matches("authorization", "cookie")).toBe(false);
+	});
+
+	it("matchers are endo's tagged records", () => {
+		const s = M.string() as unknown as Record<string | symbol, unknown>;
+		expect(s[Symbol.for("passStyle")]).toBe("tagged");
+		expect(s[Symbol.toStringTag]).toBe("match:string");
+		expect(Object.keys(s)).toEqual(["payload"]);
+		expect(s.payload).toEqual([]);
+		expect((M.any() as unknown as Record<string, unknown>).payload).toBeUndefined();
+		expect(Object.isFrozen(s)).toBe(true);
+	});
+
+	it("smallcaps: endo's encoding, round-tripped", () => {
+		expect(toSmallcaps(M.string())).toEqual({ "#tag": "match:string", payload: [] });
+		expect(toSmallcaps(M.any())).toEqual({ "#tag": "match:any", payload: "#undefined" });
+		expect(toSmallcaps("#cookie")).toBe("!#cookie");
+		expect(toSmallcaps([NaN, -0, Infinity])).toEqual(["#NaN", 0, "#Infinity"]);
+		const back = fromSmallcaps(toSmallcaps(M.string())) as Parameters<typeof matches>[1];
+		expect(matches("x", back)).toBe(true);
+		expect(matches(1, back)).toBe(false);
+		expect(fromSmallcaps("!#cookie")).toBe("#cookie");
+		expect(() => matches("x", makeTagged("match:nope", []))).toThrow("not a pattern");
+	});
+
+	it("mustMatch names the shape but not the specimen", () => {
+		expect(() => mustMatch(SECRET, "cookie", "jar: key")).toThrow('jar: key: must match "cookie"');
+		expect(() => mustMatch(SECRET, "cookie", "jar: key")).not.toThrow(SECRET);
+	});
+});
+
+describe("MapStore over RPC", () => {
+	const fresh = () => testEnv.STORE_DO.get(testEnv.STORE_DO.newUniqueId());
+
+	it("rotates: the admin's set is what the read-only view sees next", async () => {
+		const store = await fresh().cookies();
+		const rd = await store.readOnly();
+		await store.init("cookie", "session=old");
+		expect(await rd.get("cookie")).toBe("session=old");
+		await store.set("cookie", "session=new");
+		expect(await rd.entries()).toEqual([["cookie", "session=new"]]);
+	});
+
+	it("the read-only view has no write methods", async () => {
+		const store = await fresh().cookies();
+		const rd = (await store.readOnly()) as unknown as { set(k: string, v: string): Promise<void> };
+		expect(await errorOf(rd.set("cookie", SECRET))).not.toBe("");
+		expect(await store.has("cookie")).toBe(false);
+	});
+
+	it("the key shape admits only `cookie`; errors carry no values", async () => {
+		const store = await fresh().cookies();
+		const err = await errorOf(store.init("authorization", SECRET));
+		expect(err).toContain('cookie: key: must match "cookie"');
+		expect(err).not.toContain(SECRET);
+		expect(await errorOf(store.init("cookie", 42 as unknown as string))).toContain("cookie: value: must match M.string()");
+	});
+
+	it("init refuses a present key; set and get refuse a missing one", async () => {
+		const store = await fresh().cookies();
+		expect(await errorOf(store.set("cookie", SECRET))).toContain("cookie: key not found");
+		expect(await errorOf(store.get("cookie"))).toContain("cookie: key not found");
+		await store.init("cookie", SECRET);
+		const err = await errorOf(store.init("cookie", SECRET));
+		expect(err).toContain("cookie: key already registered");
+		expect(err).not.toContain(SECRET);
+	});
+
+	it("survives eviction: entries live in DO storage", async () => {
+		const stub = fresh();
+		{
+			// disposed before eviction: a live store stub holds the DO open
+			using store = await stub.cookies();
+			await store.init("cookie", "session=durable");
+		}
+		await evictDurableObject(stub);
+		using again = await stub.cookies();
+		expect(await again.get("cookie")).toBe("session=durable");
+		expect(await again.getSize()).toBe(1);
+		await again.delete("cookie");
+		expect(await again.keys()).toEqual([]);
+	});
+});
+
+describe("MapStoreDo", () => {
+	const COOKIE_SHAPES = encodeShapes({ keyShape: "cookie", valueShape: M.string() });
+	const fresh = () => testEnv.MAP_STORE_DO.get(testEnv.MAP_STORE_DO.newUniqueId());
+
+	it("keeps the shapes its creator chose, across eviction", async () => {
+		const stub = fresh();
+		await stub.configure("cookie", COOKIE_SHAPES);
+		await evictDurableObject(stub);
+		{
+			using store = await stub.store();
+			expect(await errorOf(store.init("authorization", SECRET))).toContain('cookie: key: must match "cookie"');
+			expect(await errorOf(store.init("cookie", 42))).toContain("cookie: value: must match M.string()");
+			await store.init("cookie", "session=a");
+		}
+		using rd = await stub.readOnly();
+		expect(await rd.entries()).toEqual([["cookie", "session=a"]]);
+	});
+
+	it("configures once: the same shapes again is a no-op, others are refused", async () => {
+		const stub = fresh();
+		await stub.configure("cookie", COOKIE_SHAPES);
+		await stub.configure("cookie", encodeShapes({ keyShape: "cookie", valueShape: M.string() }));
+		expect(await errorOf(stub.configure("cookie", encodeShapes({ keyShape: M.string() })))).toContain(
+			"already configured",
+		);
+		expect(await errorOf(fresh().store())).toContain("not configured");
+	});
+});

lib/tests/test-worker.ts

@@ -0,0 +1,17 @@
+/** @file the tests' main module: a DO that hosts stores on its own storage. */
+import { DurableObject } from "cloudflare:workers";
+import { M } from "../src/patterns.js";
+import { makeMapStore, type MapStore } from "../src/store.js";
+
+export { MapStoreDo } from "../src/store-do.js";
+
+/** hosts the store from the credential-rotation sketch: one key, `cookie` */
+export class StoreHost extends DurableObject {
+	cookies(): MapStore<string> {
+		return makeMapStore<string>("cookie", { keyShape: "cookie", valueShape: M.string() }, this.ctx.storage.kv);
+	}
+}
+
+export default {
+	fetch: () => new Response("store tests", { status: 404 }),
+};

lib/tests/tsconfig.json

@@ -0,0 +1,7 @@
+{
+	"extends": "../tsconfig.json",
+	"compilerOptions": {
+		"types": ["@cloudflare/vitest-plugin/types"]
+	},
+	"include": ["./**/*", "../src/**/*", "../worker-configuration.d.ts"]
+}

lib/tsconfig.json

@@ -0,0 +1,15 @@
+{
+	"compilerOptions": {
+		"target": "ES2022",
+		"module": "preserve",
+		"moduleResolution": "bundler",
+		"strict": true,
+		"esModuleInterop": true,
+		"verbatimModuleSyntax": true,
+		"skipLibCheck": true,
+		"lib": ["ES2022", "ESNext.Disposable"],
+		"noEmit": true,
+		"types": []
+	},
+	"include": ["src/**/*", "worker-configuration.d.ts"]
+}

lib/vitest.config.ts

@@ -0,0 +1,9 @@
+import { defineProject } from "vitest/config";
+import { cloudflareTest } from "@cloudflare/vitest-plugin";
+
+export default defineProject({
+	plugins: [cloudflareTest({ wrangler: { configPath: "./wrangler.tests.jsonc" } })],
+	test: {
+		include: ["tests/**/*.test.ts"],
+	},
+});

lib/wrangler.tests.jsonc

@@ -0,0 +1,17 @@
+{
+	"$schema": "node_modules/wrangler/config-schema.json",
+	// a host DO for the stores under test (lib ships no worker of its own)
+	"name": "capsite-lib-tests",
+	"main": "./tests/test-worker.ts",
+	"compatibility_date": "2026-09-29",
+	"durable_objects": {
+		"bindings": [
+			{ "name": "STORE_DO", "class_name": "StoreHost" },
+			{ "name": "MAP_STORE_DO", "class_name": "MapStoreDo" }
+		]
+	},
+	"exports": {
+		"StoreHost": { "type": "durable-object", "storage": "sqlite" },
+		"MapStoreDo": { "type": "durable-object", "storage": "sqlite" }
+	}
+}

webapp/README.md

@@ -12,19 +12,54 @@ grows past a form or two.
 
 - `GET /` — the mint form. Prefill via query string: `?url=…&headers=<urlencoded JSON>&msPerCall=…&title=…`; secret header keys (cookie, authorization, proxy-authorization) render **blank** — paste them at mint time; never echoed back. A dedicated `cookie` field is sugar for the `cookie` header (if the JSON also has one, they must agree).
 - `GET /form?render=1&…` — the same form for a proxying worker (diigo-cache's `/_connect`): the action is left as an `ACTION` placeholder for the proxy to point at its own relay.
-- `POST /` — mint. Form-encoded (that page) or JSON `{url, headers, msPerCall}` (service-style). Responds `{id}` (and `x-webapp-id`). The id is *not* logged: possession is authority.
+- `POST /` — mint. Form-encoded (that page) or JSON `{url, headers, msPerCall}` (service-style). Responds `{id, storeId}` (and `x-webapp-id`, `x-webapp-store-id`). Neither id is logged: possession is authority.
 - `POST /at/<id>` — drive an instance by capability: JSON `{path?, query?, method?, body?}` → the fluent chain → `{status, text}` (or `{error}`; messages carry no header/param values).
+- `PUT /store/<storeId>/<key>` — set a header-store entry (JSON value body), e.g. `PUT /store/<storeId>/cookie` with `"session=…"` rotates the cookie; `DELETE` removes it. → `{ok: true}` (or `{error}`; messages carry no keys or values).
 
 ## RPC surface (same-account workers; binding `entrypoint: "WebAppFactory"`)
 
 - `fetch(request)` — the HTTP surface above, over the binding
-- `newWebApp({url, headers?, msPerCall?})` → `{id, app}` — the fluent stub;
+- `newWebApp({url, headers?, msPerCall?})` → `{id, storeId, app}` — the fluent stub;
   promise pipelining makes a whole `pathjoin().query().get()` chain a
   single round trip
 - `at(id)` — the fluent stub for a previously-minted instance
+- on a stub, `postForm(fields?, echoCookies?)` → `{status, contentType,
+  contentDisposition?, location?, body}`: a multipart/form-data POST.
+  `echoCookies` maps a form field to a cookie name; the cookie's value
+  (header store included) fills the field at send, so a double-submit
+  CSRF token goes out without the holder seeing it. Redirects are not
+  followed and a non-OK status is a reply, not an Error (a 3xx to a login
+  page is how many sites say "session expired"). `location` comes back
+  query-stripped; `set-cookie` never comes back. `body` is bytes: the
+  caller knows its charset.
+- `store(storeId)` — a header store, with full authority:
+  `set("cookie", …)` rotates the cookie under every handle already out
+
+## The header store: two ids, two authorities
+
+Mint makes two things: the instance, and a header store (a `MapStoreDo`
+from [the capsite lib](../lib/src/store-do.ts), shaped
+`("cookie", { keyShape: "cookie", valueShape: M.string() })`). A `cookie`
+header goes into the store, not the instance's `init`; the instance reads
+the store's read-only view at every send.
+
+- the **instance id** is authority to *use* the cookie: it goes to the
+  cache's wiring.
+- the **store id** is authority to *choose* it: it stays with the account
+  owner, who can rotate it (log in again, `PUT`) or revoke it (`DELETE`,
+  or log out).
+
+Kept apart because whoever can choose the cookie can swap in another
+account's session: if the cache's id could rotate, a leaked instance id
+would let Mallory fill the cache (and its public page) with her own
+bookmarks, and the owner's logout would not stop it.
+
+Instances minted before header stores keep their cookie in
+`init.headers`, unchanged; they work as before and cannot rotate.
 
 ## Run
 
+    pnpm test          # header store + rotation (vitest, workerd pool)
     npx wrangler dev   # → its own ready line (usually :8787 with the
                        # two-config diigo-cache run; standalone, :8788)
 

webapp/package.json

@@ -0,0 +1,16 @@
+{
+	"name": "webapp",
+	"private": true,
+	"type": "module",
+	"scripts": {
+		"types": "wrangler types",
+		"lint": "wrangler types --check && tsc -p tsconfig.json && tsc -p tests/tsconfig.json",
+		"test": "vitest run"
+	},
+	"devDependencies": {
+		"@cloudflare/vitest-plugin": "1.3.6",
+		"typescript": "^5.9.0",
+		"vitest": "4.1.11",
+		"wrangler": "^4.148.0"
+	}
+}

webapp/src/index.ts

@@ -7,21 +7,52 @@
 // DurableObjectNamespace/DurableObjectId/DurableObjectStub are ambient types
 // in worker-configuration.d.ts (not exports of "cloudflare:workers")
 import { RpcTarget, DurableObject, WorkerEntrypoint } from "cloudflare:workers";
+import { M } from "../../lib/src/patterns.js";
+import { encodeShapes, MapStoreDo } from "../../lib/src/store-do.js";
+
+export { MapStoreDo };
 
 export type Query = Record<string, string | number>;
 type Headers = Record<string, string>;
 
+/** headers looked up at each send, e.g. a store's read-only view: whoever
+ * holds the store can rotate a credential under handles already out */
+export type HeaderMap = { entries(): [string, unknown][] | Promise<[string, unknown][]> };
+
 /**
  * init for a new instance — fixed at creation. An instance is immutable
  * authority: no re-config methods, only attenuation via the fluent chain.
+ * The one thing that changes under it is its header store's contents.
  */
 export interface WebAppInit {
 	url: string;
 	headers?: Headers;
 	/** min spacing between outbound calls, ms (0 = unthrottled) */
 	msPerCall?: number;
+	/** id of a {@link MapStoreDo} whose entries are added as headers at
+	 * each send (see {@link mintInstance}); the instance only reads it */
+	headerStore?: string;
 }
 
+/**
+ * what {@link WebApp.postForm} hands back: the status and the response
+ * headers a caller needs to tell a result from a refusal, never
+ * `set-cookie` (a credential stays where it is) and with any query
+ * stripped from `location`
+ */
+export type Reply = {
+	status: number;
+	contentType: string;
+	contentDisposition?: string;
+	location?: string;
+	/** the body as sent: the caller knows its charset (some formats name
+	 * it in their own header, not in content-type) */
+	body: Uint8Array;
+};
+
+/** one outbound request, redirects not followed; the DO's gate and fetch */
+export type Exchange = (url: string, headers: Headers, method: "POST", body: FormData) => Promise<Response>;
+
 /** structural type of a stub handle: chain to narrow, then fire */
 export interface FluentGet {
 	pathjoin(ref: string): FluentGet;
@@ -29,8 +60,10 @@ export interface FluentGet {
 	withHeaders(h: Headers): FluentGet;
 	withHeader(key: string, value: string): FluentGet;
 	cookies(cookie: string): FluentGet;
+	withHeaderMap(map: HeaderMap): FluentGet;
 	get(): Promise<string>;
 	post(body: string): Promise<string>;
+	postForm(fields?: Record<string, string>, echoCookies?: Record<string, string>): Promise<Reply>;
 }
 
 /**
@@ -57,17 +90,23 @@ export interface FluentGet {
 export class WebApp extends RpcTarget implements FluentGet {
 	#url: string;
 	#headers: Headers;
+	#maps: readonly HeaderMap[];
 	#send: (url: string, headers: Headers, method: "GET" | "POST", body?: string) => Promise<string>;
+	#exchange: Exchange;
 
 	constructor(
 		url: string,
 		headers: Headers,
+		maps: readonly HeaderMap[],
 		send: (url: string, headers: Headers, method: "GET" | "POST", body?: string) => Promise<string>,
+		exchange: Exchange,
 	) {
 		super();
 		this.#url = url;
 		this.#headers = headers;
+		this.#maps = maps;
 		this.#send = send;
+		this.#exchange = exchange;
 	}
 
 	/** Join a relative path, merging the base's query.
@@ -85,13 +124,13 @@ export class WebApp extends RpcTarget implements FluentGet {
 			throw new Error(`pathjoin: ${ref} not within ${hereNoQuery.href}`);
 		}
 		const baseParams: Query = Object.fromEntries(here.searchParams);
-		return new WebApp(unionQuery(there.href, baseParams), this.#headers, this.#send);
+		return new WebApp(unionQuery(there.href, baseParams), this.#headers, this.#maps, this.#send, this.#exchange);
 	}
 
 	/** Union headers, flower-style (see {@link WebApp}): a shared key with a
 	 * different value throws; the same value is fine. */
 	withHeaders(h: Headers): WebApp {
-		return new WebApp(this.#url, unionHeaders(this.#headers, h), this.#send);
+		return new WebApp(this.#url, unionHeaders(this.#headers, h), this.#maps, this.#send, this.#exchange);
 	}
 
 	/** one key, flower-style (see {@link WebApp}) */
@@ -105,15 +144,72 @@ export class WebApp extends RpcTarget implements FluentGet {
 
 	/** Union params into the existing query, flower-style (see {@link WebApp}). */
 	query(params: Query): WebApp {
-		return new WebApp(unionQuery(this.#url, params), this.#headers, this.#send);
+		return new WebApp(unionQuery(this.#url, params), this.#headers, this.#maps, this.#send, this.#exchange);
+	}
+
+	/** Add headers read from `map` at each send, unioned flower-style (see
+	 * {@link WebApp}) with the rest — so a contradiction surfaces at send. */
+	withHeaderMap(map: HeaderMap): WebApp {
+		return new WebApp(this.#url, this.#headers, [...this.#maps, map], this.#send, this.#exchange);
 	}
 
 	async get(): Promise<string> {
-		return this.#send(this.#url, this.#headers, "GET");
+		return this.#send(this.#url, await this.#headersNow(), "GET");
 	}
 
 	async post(body: string): Promise<string> {
-		return this.#send(this.#url, this.#headers, "POST", body);
+		return this.#send(this.#url, await this.#headersNow(), "POST", body);
+	}
+
+	/**
+	 * POST `fields` as multipart/form-data. `echoCookies` maps a form field
+	 * to a cookie name: at send, that cookie's value (from the headers,
+	 * header store included) goes in the field, so a double-submit CSRF
+	 * token can be sent by a holder who never sees it.
+	 *
+	 * Unlike `get`/`post`, a non-OK status is a {@link Reply}, not an
+	 * Error, and redirects are not followed: a 3xx to a login page is how
+	 * many sites say "session expired".
+	 */
+	async postForm(fields: Record<string, string> = {}, echoCookies: Record<string, string> = {}): Promise<Reply> {
+		const headers = await this.#headersNow();
+		if (Object.keys(headers).some((k) => k.toLowerCase() === "content-type")) {
+			throw new Error("postForm: content-type is set by the form, not the headers");
+		}
+		const jar = parseCookies(
+			Object.entries(headers).find(([k]) => k.toLowerCase() === "cookie")?.[1] ?? "",
+		);
+		const form = new FormData();
+		for (const [name, value] of Object.entries(fields)) form.append(name, value);
+		for (const [field, cookie] of Object.entries(echoCookies)) {
+			// names only: values must not appear in Error messages
+			if (field in fields) throw new Error(`postForm: contradicts on ${field}`);
+			const value = jar.get(cookie);
+			if (value === undefined) throw new Error(`postForm: no ${cookie} cookie to echo`);
+			form.append(field, value);
+		}
+		const res = await this.#exchange(this.#url, headers, "POST", form);
+		const location = res.headers.get("location");
+		return {
+			status: res.status,
+			contentType: res.headers.get("content-type") ?? "",
+			...withDefined("contentDisposition", res.headers.get("content-disposition")),
+			...withDefined("location", location === null ? null : stripQuery(location, this.#url)),
+			body: new Uint8Array(await res.arrayBuffer()),
+		};
+	}
+
+	async #headersNow(): Promise<Headers> {
+		let headers = this.#headers;
+		for (const map of this.#maps) {
+			const entries = await map.entries();
+			for (const [key, value] of entries) {
+				// key name only: header values must not appear in Error messages
+				if (typeof value !== "string") throw new Error(`headers: ${key} is not a string`);
+			}
+			headers = unionHeaders(headers, Object.fromEntries(entries) as Headers);
+		}
+		return headers;
 	}
 }
 
@@ -149,11 +245,16 @@ class Gate {
  * storage, surviving eviction (instance memory evaporates when the DO naps;
  * storage is where "this instance means this URL" durably lives).
  *
+ * Its cookie, when minted by {@link mintInstance}, is not in `init` but in
+ * the header store, whose id goes to the account owner and not to whoever
+ * holds the instance id: the owner can rotate it, and the holder cannot
+ * swap in another account's session.
+ *
  * @see https://developers.cloudflare.com/durable-objects/ — newUniqueId is
  * unforgeable (128-bit, inderivable); idFromName by contrast is ambient:
  * any worker with the namespace binding can recompute it
  */
-export class WebAppDo extends DurableObject<{ WEBAPP?: never }> {
+export class WebAppDo extends DurableObject<WebAppEnv> {
 	#ready?: Promise<void>;
 
 	/** one-shot configuration; a different-url re-configure is refused */
@@ -207,16 +308,46 @@ export class WebAppDo extends DurableObject<{ WEBAPP?: never }> {
 			}
 			return res.text();
 		};
-		return new WebApp(init.url, init.headers ?? {}, send);
+		const exchange: Exchange = async (url, headers, method, body) => {
+			await gate.waitMyTurn();
+			return fetch(url, { method, headers, body, redirect: "manual" });
+		};
+		const maps = init.headerStore === undefined ? [] : [this.#readHeaderStore(init.headerStore)];
+		return new WebApp(init.url, init.headers ?? {}, maps, send, exchange);
+	}
+
+	/** a header map reading the store's read-only view, afresh at each send */
+	#readHeaderStore(storeId: string): HeaderMap {
+		const ns = this.env.MAP_STORE_DO;
+		const store = ns.get(ns.idFromString(storeId));
+		return {
+			async entries() {
+				using rd = await store.readOnly();
+				return await rd.entries();
+			},
+		};
 	}
 }
 
+/** split the cookie (any case of the header name) from the other headers */
+function splitCookie(headers: Headers): { cookie?: string; rest: Headers } {
+	const rest: Headers = {};
+	let cookie: string | undefined;
+	for (const [key, value] of Object.entries(headers)) {
+		if (key.toLowerCase() === "cookie") cookie = value;
+		else rest[key] = value;
+	}
+	return { cookie, rest };
+}
+
+type WebAppEnv = {
+	WEBAPP_DO: DurableObjectNamespace<WebAppDo>;
+	MAP_STORE_DO: DurableObjectNamespace<MapStoreDo>;
+};
+
 /** the worker's whole HTTP surface (the default export and the
  * WebAppFactory entrypoint share it) */
-const defaultFetch = async (
+const defaultFetch = async (request: Request, env: WebAppEnv): Promise<Response> => {
-	request: Request,
-	env: { WEBAPP_DO: DurableObjectNamespace<WebAppDo> },
-): Promise<Response> => {
 	const url = new URL(request.url);
 
 	// mint form: site-agnostic; secret headers (cookie, authorization) are
@@ -227,7 +358,7 @@ const defaultFetch = async (
 
 	// mint: browser form POST (form-encoded) or JSON (service-style)
 	if (url.pathname === "/" && request.method === "POST") {
-		return mint(request, env.WEBAPP_DO);
+		return mint(request, env);
 	}
 
 	// the mint form, renderable for a proxying worker: ?render=1 keeps the
@@ -246,6 +377,14 @@ const defaultFetch = async (
 		return drive(await app, request);
 	}
 
+	// a header store, by its id (the owner's, not the instance's): PUT
+	// JSON value sets a key (e.g. rotates the cookie), DELETE removes it
+	const entry = url.pathname.match(/^\/store\/([A-Za-z0-9-]+)\/([^/]+)$/);
+	if (entry && (request.method === "PUT" || request.method === "DELETE")) {
+		const store = env.MAP_STORE_DO.get(env.MAP_STORE_DO.idFromString(entry[1]));
+		return storeEntry(store, decodeURIComponent(entry[2]), request);
+	}
+
 	return new Response("not found", { status: 404 });
 };
 
@@ -305,10 +444,7 @@ function withCookie(init: WebAppInit, cookie: string): WebAppInit {
 }
 
 /** mint a fresh instance from form-encoded or JSON input */
-async function mint(
+async function mint(request: Request, env: WebAppEnv): Promise<Response> {
-	request: Request,
-	ns: DurableObjectNamespace<WebAppDo>,
-): Promise<Response> {
 	const ct = request.headers.get("content-type") ?? "";
 	let init: WebAppInit;
 	try {
@@ -335,13 +471,35 @@ async function mint(
 		return Response.json({ error: "bad url" }, { status: 400 });
 	}
 
-	const id = ns.newUniqueId();
+	const { id, storeId } = await mintInstance(env, init);
-	const instance = ns.get(id);
+	// note: ids intentionally NOT logged — they are bearer capabilities
-	await instance.configure(init);
-	const app = await instance.handle();
-	// note: id intentionally NOT logged — it is a bearer capability
 	console.log({ event: "mint", msPerCall: init.msPerCall });
-	return Response.json({ id: id.toString() }, { headers: { "x-webapp-id": id.toString() } });
+	return Response.json({ id, storeId }, { headers: { "x-webapp-id": id, "x-webapp-store-id": storeId } });
+}
+
+/**
+ * a configured instance plus its header store, shaped to hold just the
+ * cookie: the instance id is authority to use the cookie; the store id
+ * (for the account owner) is authority to rotate or remove it. Any
+ * `cookie` header in `init` goes to the store, not to the instance.
+ */
+async function mintInstance(env: WebAppEnv, init: WebAppInit): Promise<{ id: string; storeId: string }> {
+	const { cookie, rest } = splitCookie(init.headers ?? {});
+	const storeId = env.MAP_STORE_DO.newUniqueId();
+	const store = env.MAP_STORE_DO.get(storeId);
+	await store.configure("cookie", encodeShapes({ keyShape: "cookie", valueShape: M.string() }));
+	if (cookie !== undefined) {
+		using full = await store.store();
+		await full.init("cookie", cookie);
+	}
+	const id = env.WEBAPP_DO.newUniqueId();
+	await env.WEBAPP_DO.get(id).configure({
+		url: init.url,
+		headers: rest,
+		...(init.msPerCall === undefined ? {} : { msPerCall: init.msPerCall }),
+		headerStore: storeId.toString(),
+	});
+	return { id: id.toString(), storeId: storeId.toString() };
 }
 
 /** drive a handle from the /at/<id> JSON protocol (also used by the
@@ -368,6 +526,60 @@ async function drive(app: FluentGet, request: Request): Promise<Response> {
 	}
 }
 
+/** the /store/<id>/<key> protocol: PUT a JSON value (set, or init if
+ * absent), or DELETE → {ok} (or {error}; messages carry no values) */
+async function storeEntry(store: DurableObjectStub<MapStoreDo>, key: string, request: Request): Promise<Response> {
+	let value: unknown;
+	if (request.method === "PUT") {
+		try {
+			value = await request.json();
+		} catch (err) {
+			return Response.json({ error: `bad input: ${String(err)}` }, { status: 400 });
+		}
+	}
+	try {
+		using full = await store.store();
+		if (request.method === "DELETE") {
+			if (await full.has(key)) await full.delete(key);
+		} else if (await full.has(key)) {
+			await full.set(key, value);
+		} else {
+			await full.init(key, value);
+		}
+	} catch (err) {
+		// store errors name shapes, never keys or values (see lib/src/store.ts)
+		return Response.json({ error: String(err) }, { status: 400 });
+	}
+	// note: neither id nor value logged
+	console.log({ event: "store", method: request.method });
+	return Response.json({ ok: true });
+}
+
+/** a cookie header's name → value (the first of a repeated name wins) */
+function parseCookies(header: string): Map<string, string> {
+	const jar = new Map<string, string>();
+	for (const pair of header.split(";")) {
+		const eq = pair.indexOf("=");
+		if (eq < 0) continue;
+		const name = pair.slice(0, eq).trim();
+		if (name && !jar.has(name)) jar.set(name, pair.slice(eq + 1).trim());
+	}
+	return jar;
+}
+
+/** `ref` resolved against `base`, query and fragment dropped: they can carry credentials */
+function stripQuery(ref: string, base: string): string {
+	const url = new URL(ref, base);
+	url.search = "";
+	url.hash = "";
+	return url.href;
+}
+
+/** `{[key]: value}`, or `{}` when value is null: optional fields stay absent */
+function withDefined<K extends string>(key: K, value: string | null): { [P in K]?: string } {
+	return (value === null ? {} : { [key]: value }) as { [P in K]?: string };
+}
+
 function unionHeaders(base: Headers, more: Headers): Headers {
 	const merged = { ...base };
 	for (const [key, value] of Object.entries(more)) {
@@ -396,37 +608,37 @@ function unionQuery(base: string, params: Query): string {
 /**
  * the RPC service of the webapp worker. Flow:
  *
- *   const { id, app } = await env.WEBAPP.newWebApp({
+ *   const { id, storeId, app } = await env.WEBAPP.newWebApp({
- *     url: "https://api.github.com", headers: { authorization: `Bearer ${t}` },
+ *     url: "https://diigo.example/", headers: { cookie: c },
  *     msPerCall: 250,
  *   });
  *   // hold id (persist it, hand it to workers you trust), then e.g.:
  *   const text = await app.query({ per_page: 5 }).get();
  *   // later, from another worker (same account) holding the id:
  *   const app2 = env.WEBAPP.at(id);
+ *   // the account owner, holding storeId, after logging in again:
+ *   await (await env.WEBAPP.store(storeId)).set("cookie", c2);
  */
 export class WebAppFactory extends WorkerEntrypoint {
 	/** the same HTTP surface as the default export, over the entrypoint
 	 * (for service-binding callers that proxy pages, e.g. diigo-cache's
 	 * /_connect → this form) */
 	async fetch(request: Request): Promise<Response> {
-		const env = this.env as { WEBAPP_DO: DurableObjectNamespace<WebAppDo> };
+		return defaultFetch(request, this.env);
-		return defaultFetch(request, env);
 	}
 
-	/** mint a fresh instance: unforgeable uniqueId + configured fluent stub.
+	/** mint a fresh instance: unforgeable uniqueId + configured fluent stub,
-	 * The caller decides who else ever learns the id. (If the caller only
+	 * plus the id of its header store (see {@link mintInstance}). The
+	 * caller decides who else ever learns either id. (If the caller only
 	 * wanted the id, it must dispose() the app stub — workerd warns about
 	 * undisposed stubs; see the `at()` alternative + `/at/<id>` route for
 	 * id-only flows.) */
-	async newWebApp(init: WebAppInit): Promise<{ id: string; app: FluentGet }> {
+	async newWebApp(init: WebAppInit): Promise<{ id: string; storeId: string; app: FluentGet }> {
 		new URL(init.url); // fail before minting on garbage
+		const { id, storeId } = await mintInstance(this.env, init);
 		const ns = this.env.WEBAPP_DO;
-		const id = ns.newUniqueId();
+		const app = await ns.get(ns.idFromString(id)).handle();
-		const instance = ns.get(id);
+		return { id, storeId, app };
-		await instance.configure(init);
-		const app = await instance.handle();
-		return { id: id.toString(), app };
 	}
 
 	/** reconnect by a previously-obtained id */
@@ -434,6 +646,13 @@ export class WebAppFactory extends WorkerEntrypoint {
 		const ns = this.env.WEBAPP_DO;
 		return ns.get(ns.idFromString(id)).handle();
 	}
+
+	/** a header store by its id, with full authority (the instance id
+	 * reaches none: see {@link mintInstance}) */
+	async store(storeId: string) {
+		const ns = this.env.MAP_STORE_DO;
+		return ns.get(ns.idFromString(storeId)).store();
+	}
 }
 function sleep(ms: number): Promise<void> {
 	return new Promise((r) => setTimeout(r, ms));

webapp/tests/cookie.test.ts

@@ -0,0 +1,131 @@
+import { env } from "cloudflare:workers";
+import { runInDurableObject } from "cloudflare:test";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import worker, { type WebAppInit } from "../src/index.js";
+
+type TestEnv = {
+	WEBAPP_DO: DurableObjectNamespace<import("../src/index.js").WebAppDo>;
+	MAP_STORE_DO: DurableObjectNamespace<import("../src/index.js").MapStoreDo>;
+};
+const testEnv = env as unknown as TestEnv;
+
+const URL_ = "https://diigo.example/api/";
+
+/** the cookie header of each outbound fetch */
+function spyCookies(): (string | null)[] {
+	const seen: (string | null)[] = [];
+	vi.spyOn(globalThis, "fetch").mockImplementation(async (_input, init) => {
+		seen.push(new Headers(init?.headers).get("cookie"));
+		return new Response("ok");
+	});
+	return seen;
+}
+
+afterEach(() => {
+	vi.restoreAllMocks();
+});
+
+/** the worker's HTTP surface, as a JSON client */
+const call = (path: string, method: string, body?: unknown) =>
+	worker.fetch(
+		new Request(`https://webapp.example${path}`, {
+			method,
+			body: body === undefined ? undefined : JSON.stringify(body),
+			headers: { "content-type": "application/json" },
+		}),
+		testEnv,
+	);
+
+const mint = async (init: WebAppInit) => {
+	const { id, storeId } = (await (await call("/", "POST", init)).json()) as { id: string; storeId: string };
+	const instance = testEnv.WEBAPP_DO.get(testEnv.WEBAPP_DO.idFromString(id));
+	return { id, storeId, instance };
+};
+
+/** the failure of a call: its error status, or what it threw; "" if it succeeds */
+async function errorOf(response: Promise<Response>): Promise<string> {
+	try {
+		const res = await response;
+		return res.ok ? "" : `${res.status} ${await res.text()}`;
+	} catch (err) {
+		return String(err);
+	}
+}
+
+/** `init` as stored */
+const storedInit = (stub: DurableObjectStub) =>
+	runInDurableObject(stub, (_obj, state) => state.storage.kv.get<WebAppInit>("init"));
+
+describe("cookie rotation", () => {
+	it("mint puts the cookie in the header store, not init; sends carry it", async () => {
+		const seen = spyCookies();
+		const { storeId, instance } = await mint({
+			url: URL_,
+			headers: { Cookie: "session=a", accept: "application/json" },
+		});
+		expect(await storedInit(instance)).toEqual({
+			url: URL_,
+			headers: { accept: "application/json" },
+			headerStore: storeId,
+		});
+		using app = await instance.handle();
+		await app.get();
+		expect(seen).toEqual(["session=a"]);
+	});
+
+	it("the store id rotates under handles already out, and revokes", async () => {
+		const seen = spyCookies();
+		const { storeId, instance } = await mint({ url: URL_, headers: { cookie: "session=a" } });
+		using app = await instance.handle();
+		await app.pathjoin("x").get();
+		expect(await (await call(`/store/${storeId}/cookie`, "PUT", "session=b")).json()).toEqual({ ok: true });
+		await app.pathjoin("x").get();
+		expect(await (await call(`/store/${storeId}/cookie`, "DELETE")).json()).toEqual({ ok: true });
+		await app.get();
+		expect(seen).toEqual(["session=a", "session=b", null]);
+	});
+
+	it("the instance id reaches no store: its holder cannot swap in another session", async () => {
+		const seen = spyCookies();
+		const { id, instance } = await mint({ url: URL_, headers: { cookie: "session=alice" } });
+		expect(await errorOf(call(`/store/${id}/cookie`, "PUT", "session=mallory"))).not.toBe("");
+		expect((await call(`/at/${id}/cookie`, "POST", { cookie: "session=mallory" })).status).toBe(404);
+		using app = await instance.handle();
+		await app.get();
+		expect(seen).toEqual(["session=alice"]);
+	});
+
+	it("the store's shapes admit only the cookie; errors carry no values", async () => {
+		const { storeId } = await mint({ url: URL_ });
+		const err = await errorOf(call(`/store/${storeId}/authorization`, "PUT", "Bearer s3kr1t"));
+		expect(err).toContain('cookie: key: must match \\"cookie\\"');
+		expect(err).not.toContain("s3kr1t");
+		expect(await errorOf(call(`/store/${storeId}/cookie`, "PUT", 42))).toContain("must match M.string()");
+	});
+
+	it("an instance minted before header stores keeps its cookie in init, untouched", async () => {
+		const seen = spyCookies();
+		const instance = testEnv.WEBAPP_DO.get(testEnv.WEBAPP_DO.newUniqueId());
+		const old = { url: URL_, headers: { cookie: "session=old" }, msPerCall: 0 };
+		await runInDurableObject(instance, (_obj, state) => state.storage.put("init", old));
+		using app = await instance.handle();
+		await app.get();
+		expect(seen).toEqual(["session=old"]);
+		expect(await storedInit(instance)).toEqual(old);
+	});
+
+	it("a fixed header contradicting the stored cookie fails at send, naming no values", async () => {
+		spyCookies();
+		const { instance } = await mint({ url: URL_, headers: { cookie: "session=a" } });
+		using app = await instance.handle();
+		const err = await app
+			.withHeader("cookie", "session=mine")
+			.get()
+			.then(
+				() => "",
+				(e: unknown) => String(e),
+			);
+		expect(err).toContain("headers: contradicts on cookie");
+		expect(err).not.toContain("session=");
+	});
+});

webapp/tests/post-form.test.ts

@@ -0,0 +1,117 @@
+import { env } from "cloudflare:workers";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import worker, { type WebAppInit } from "../src/index.js";
+
+type TestEnv = {
+	WEBAPP_DO: DurableObjectNamespace<import("../src/index.js").WebAppDo>;
+	MAP_STORE_DO: DurableObjectNamespace<import("../src/index.js").MapStoreDo>;
+};
+const testEnv = env as unknown as TestEnv;
+
+const URL_ = "https://site.example/app/export/7/data";
+
+type Seen = { url: string; redirect?: string; contentType: string | null; form: Record<string, string> };
+
+/** each outbound fetch, its form fields read back; answers with `res()` */
+function spyForms(res: () => Response): Seen[] {
+	const seen: Seen[] = [];
+	vi.spyOn(globalThis, "fetch").mockImplementation(async (input, init) => {
+		const req = new Request(input as string, init as RequestInit);
+		const form = Object.fromEntries([...(await req.formData()).entries()].map(([k, v]) => [k, String(v)]));
+		seen.push({ url: req.url, redirect: init?.redirect, contentType: req.headers.get("content-type"), form });
+		return res();
+	});
+	return seen;
+}
+
+afterEach(() => {
+	vi.restoreAllMocks();
+});
+
+const mint = async (init: WebAppInit) => {
+	const res = await worker.fetch(
+		new Request("https://webapp.example/", {
+			method: "POST",
+			body: JSON.stringify(init),
+			headers: { "content-type": "application/json" },
+		}),
+		testEnv,
+	);
+	const { id, storeId } = (await res.json()) as { id: string; storeId: string };
+	return { id, storeId, instance: testEnv.WEBAPP_DO.get(testEnv.WEBAPP_DO.idFromString(id)) };
+};
+
+/** the failure of a call: what it threw; "" if it succeeds */
+async function errorOf(p: Promise<unknown>): Promise<string> {
+	try {
+		await p;
+		return "";
+	} catch (err) {
+		return String(err);
+	}
+}
+
+describe("postForm", () => {
+	it("echoes a cookie from the header store into a form field; the holder never sees it", async () => {
+		const seen = spyForms(
+			() =>
+				new Response("col1,col2", {
+					headers: {
+						"content-type": "text/csv",
+						"content-disposition": 'attachment;filename="x.csv"',
+						"set-cookie": "sess=next; HttpOnly",
+					},
+				}),
+		);
+		const { instance } = await mint({ url: URL_, headers: { cookie: "a=1; tok=s3cret; b=2" } });
+		using app = await instance.handle();
+		const reply = await app.query({ since: "2026-07-13\x1f" }).postForm({ kind: "all" }, { csrf: "tok" });
+		expect(seen).toEqual([
+			{
+				url: `${URL_}?since=2026-07-13%1F`,
+				redirect: "manual",
+				contentType: expect.stringMatching(/^multipart\/form-data; boundary=/),
+				form: { kind: "all", csrf: "s3cret" },
+			},
+		]);
+		expect(reply).toEqual({
+			status: 200,
+			contentType: "text/csv",
+			contentDisposition: 'attachment;filename="x.csv"',
+			body: new TextEncoder().encode("col1,col2"),
+		});
+	});
+
+	it("does not follow a redirect: the 3xx comes back, location query-stripped", async () => {
+		spyForms(() => new Response(null, { status: 302, headers: { location: "/login?next=s3cret#x" } }));
+		const { instance } = await mint({ url: URL_, headers: { cookie: "tok=t" } });
+		using app = await instance.handle();
+		const reply = await app.postForm({}, { csrf: "tok" });
+		expect(reply).toEqual({ status: 302, contentType: "", location: "https://site.example/login", body: new Uint8Array() });
+	});
+
+	it("refuses, naming no values: a missing cookie, a field set twice, a content-type header", async () => {
+		spyForms(() => new Response("ok"));
+		const { instance } = await mint({ url: URL_, headers: { cookie: "tok=s3cret" } });
+		using app = await instance.handle();
+		expect(await errorOf(app.postForm({}, { csrf: "nope" }))).toMatch(/no nope cookie to echo/);
+		const twice = await errorOf(app.postForm({ csrf: "mine" }, { csrf: "tok" }));
+		expect(twice).toMatch(/contradicts on csrf/);
+		expect(twice).not.toMatch(/s3cret|mine/);
+		const typed = app.withHeader("content-type", "text/plain");
+		expect(await errorOf(typed.postForm())).toMatch(/content-type is set by the form/);
+	});
+
+	it("rotating the store's cookie changes what is echoed", async () => {
+		const seen = spyForms(() => new Response("ok"));
+		const { storeId, instance } = await mint({ url: URL_, headers: { cookie: "tok=one" } });
+		using app = await instance.handle();
+		await app.postForm({}, { csrf: "tok" });
+		await worker.fetch(
+			new Request(`https://webapp.example/store/${storeId}/cookie`, { method: "PUT", body: JSON.stringify("tok=two") }),
+			testEnv,
+		);
+		await app.postForm({}, { csrf: "tok" });
+		expect(seen.map((s) => s.form.csrf)).toEqual(["one", "two"]);
+	});
+});

webapp/tests/tsconfig.json

@@ -0,0 +1,7 @@
+{
+	"extends": "../tsconfig.json",
+	"compilerOptions": {
+		"types": ["@cloudflare/vitest-plugin/types"]
+	},
+	"include": ["./**/*", "../worker-configuration.d.ts"]
+}

webapp/tsconfig.json

@@ -7,6 +7,7 @@
 		"esModuleInterop": true,
 		"verbatimModuleSyntax": true,
 		"skipLibCheck": true,
+		"lib": ["ES2022", "ESNext.Disposable"],
 		"noEmit": true,
 		"types": []
 	},

webapp/vitest.config.ts

@@ -0,0 +1,9 @@
+import { defineProject } from "vitest/config";
+import { cloudflareTest } from "@cloudflare/vitest-plugin";
+
+export default defineProject({
+	plugins: [cloudflareTest({ wrangler: { configPath: "./wrangler.jsonc" } })],
+	test: {
+		include: ["tests/**/*.test.ts"],
+	},
+});

webapp/wrangler.jsonc

@@ -5,7 +5,13 @@
 	"compatibility_date": "2026-09-29",
 	"observability": { "enabled": true },
 	"durable_objects": {
-		"bindings": [{ "name": "WEBAPP_DO", "class_name": "WebAppDo" }]
+		"bindings": [
+			{ "name": "WEBAPP_DO", "class_name": "WebAppDo" },
+			{ "name": "MAP_STORE_DO", "class_name": "MapStoreDo" }
+		]
 	},
-	"migrations": [{ "tag": "v1", "new_sqlite_classes": ["WebAppDo"] }]
+	"migrations": [
+		{ "tag": "v1", "new_sqlite_classes": ["WebAppDo"] },
+		{ "tag": "v2", "new_sqlite_classes": ["MapStoreDo"] }
+	]
 }