fix(astro): persist session delete without prior get/set

.changeset/persist-session-delete-without-prior-mutation.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes session persistence when `session.delete()` is the first mutation in a request (no prior `get`, `set`, `has`, or `keys`). The session was marked dirty in memory, but persistence skipped the save because `#data` stayed `undefined`, so the backing store could still return the deleted key on the next request.

packages/astro/e2e/view-transitions.test.ts

@@ -25,9 +25,10 @@ test.afterAll(async () => {
 
 function collectLoads(page: Page) {
 	const loads: string[] = [];
-	page.on('load', async () => {
+	// Push synchronously; an async handler awaiting `page.title()` races with assertions (often on Firefox).
+	page.on('load', () => {
 		const url = page.url();
-		if (url !== 'about:blank') loads.push(await page.title());
+		if (url !== 'about:blank') loads.push(url);
 	});
 	return loads;
 }
@@ -147,7 +148,7 @@ test.describe('View Transitions', () => {
 
 		expect(
 			loads.length,
-			'There should be 2 page loads. The original, then going from 3 to 2',
+			'There should be 2 page loads. The initial navigation, then the full navigation from page 1 to page 3',
 		).toEqual(2);
 	});
 

packages/astro/src/core/session/runtime.ts

@@ -154,7 +154,8 @@ export class AstroSession {
 	 * Deletes a session value.
 	 */
 	delete(key: string) {
-		this.#data?.delete(key);
+		this.#data ??= new Map();
+		this.#data.delete(key);
 		if (this.#partial) {
 			this.#toDelete.add(key);
 		}

packages/astro/test/units/sessions/astro-session.test.ts

@@ -385,15 +385,41 @@ describe('AstroSession - Sparse Data Operations', () => {
 		session.delete('key');
 		await session[PERSIST_SYMBOL]();
 
-		// Create a new session using the stored data
+		// Create a new session using the stored data (get must return parsed JSON like unstorage)
 		const newSession = createSession(defaultConfig, defaultMockCookies, {
-			get: async () => storedData,
+			get: async () => (storedData != null ? JSON.parse(storedData) : null),
 			setItem: async () => {},
 		} as unknown as Storage);
 
 		assert.equal(await newSession.get('key'), undefined);
 	});
 
+	it('should persist delete as the first mutation (no prior get/set)', async () => {
+		const store = new Map<string, string>();
+		const sessionId = 'sessionid';
+		store.set(sessionId, devalueStringify(new Map([['token', { data: 'secret' }]])));
+
+		const mockStorage = {
+			get: async (key: string) => {
+				const raw = store.get(key);
+				return raw ? JSON.parse(raw) : null;
+			},
+			setItem: async (key: string, value: string) => {
+				store.set(key, value);
+			},
+			removeItem: async (key: string) => {
+				store.delete(key);
+			},
+		} as unknown as Storage;
+
+		const session = createSession(defaultConfig, defaultMockCookies, mockStorage);
+		session.delete('token');
+		await session[PERSIST_SYMBOL]();
+
+		const newSession = createSession(defaultConfig, defaultMockCookies, mockStorage);
+		assert.equal(await newSession.get('token'), undefined);
+	});
+
 	it('should update existing values in sparse mode', async () => {
 		const existingData = stringify(new Map([['key', 'old']]));
 		const mockStorage = {