diff --git a/AGENTS.md b/AGENTS.md
index d1e1ae70..d2b590e2 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -22,7 +22,11 @@ deviating from agreed scope or product behavior.
 Target **9/10+ for minimalness, elegance, and correctness**: the smallest complete
 solution, clear ownership, and no known material defects. Prefer existing patterns
 and subtraction. No opportunistic refactors, speculative abstractions, or new
-features disguised as fixes. If the fix keeps growing, revisit the cause and scope.
+features disguised as fixes. Before expanding into another shared subsystem or
+adding alternate-adapter support, show the human the scope change and smallest
+complete alternative. Require a current caller or explicit approval for adapter
+parity. Review necessity separately from correctness; passing tests do not justify
+scope growth. Split at real ownership boundaries, not by deleting safety coverage.
 
 Keep files cohesive and group modules and tests by owner. Treat size as a review
 signal, not a quota. Extract stable boundaries only when they simplify the
diff --git a/dev/agent-observer.test.mjs b/dev/agent-observer.test.mjs
index b113e130..46aef126 100644
--- a/dev/agent-observer.test.mjs
+++ b/dev/agent-observer.test.mjs
@@ -1,4 +1,4 @@
-import { test, expect } from "vitest";
+import { test, expect, vi, beforeEach, afterEach } from "vitest";
 import {
   finalizeEvent,
   generateSecretKey,
@@ -7,6 +7,12 @@ import {
 } from "nostr-tools";
 import { decodeAgentObserver } from "./agent-observer.mjs";
 
+// Keep frame construction and validation in the same second at the ±300s boundary.
+beforeEach(() => {
+  vi.spyOn(Date, "now").mockReturnValue(1700000000999);
+});
+afterEach(() => vi.restoreAllMocks());
+
 const owner = generateSecretKey(),
   agent = generateSecretKey(),
   stranger = generateSecretKey();
diff --git a/docs/browser-testing.md b/docs/browser-testing.md
index ef93fb08..6b6975a2 100644
--- a/docs/browser-testing.md
+++ b/docs/browser-testing.md
@@ -344,3 +344,13 @@ focused visible dwell, non-reading opening/composer focus, individual markers,
 encrypted publication/readback, reload, cancellation and local manual-unread.
 The reload control holds network content so verified disk-restore wiring is required.
 This is not a deployed-relay, native signer or cross-device integration test.
+
+## Fixture server isolation
+
+Concurrent Vite fixture servers must own separate optimizer caches. Use
+`tests/browser/vite-server.mjs` for new fixtures; its `close()` releases the owned
+cache. The existing emoji and conversation fixtures retain their explicitly owned
+temporary caches. Do not share Vite's default `node_modules/.vite`: another server
+can invalidate dependency imports and leave a blank fixture with a 504
+`Outdated Optimize Dep`. Keep import failures visible; retries or longer UI waits
+do not repair module loading.
diff --git a/tests/browser/agents.spec.mjs b/tests/browser/agents.spec.mjs
index f802408a..7c69a256 100644
--- a/tests/browser/agents.spec.mjs
+++ b/tests/browser/agents.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
@@ -16,8 +16,8 @@ test("My agents reads the existing library with exact linked keys and session-sa
   });
   const errors = [];
   page.on("pageerror", (error) => errors.push(String(error)));
-  await server.listen();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/agents.html`,
     );
diff --git a/tests/browser/avatar-loading.spec.mjs b/tests/browser/avatar-loading.spec.mjs
index f016a10a..b9aac32b 100644
--- a/tests/browser/avatar-loading.spec.mjs
+++ b/tests/browser/avatar-loading.spec.mjs
@@ -1,5 +1,5 @@
 import { expect, test } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
@@ -14,8 +14,8 @@ test("shared avatars defer offscreen artwork, omit the referrer and recover from
     logLevel: "error",
     server: { host: "127.0.0.1", port: 0, strictPort: false },
   });
-  await server.listen();
   try {
+    await server.listen();
     const requests = [];
     await page.route("https://images.example/avatar.png", async (route) => {
       requests.push(route.request().headers());
diff --git a/tests/browser/image-scroll.spec.mjs b/tests/browser/image-scroll.spec.mjs
index a0b56491..cdf724df 100644
--- a/tests/browser/image-scroll.spec.mjs
+++ b/tests/browser/image-scroll.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 import { settle, anchor, expectAnchor } from "./timeline.mjs";
@@ -54,7 +54,6 @@ async function fixtureServer() {
 test("delayed and failed images preserve bottom and reading anchors across remounts", async ({
   page,
 }, testInfo) => {
-  const server = await fixtureServer();
   const pending = new Set();
   const requests = new Map();
   let held = true;
@@ -102,8 +101,9 @@ test("delayed and failed images preserve bottom and reading anchors across remou
         ),
       )
       .toBe(true);
-  await server.listen();
+  const server = await fixtureServer();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/image-scroll.html`,
     );
@@ -180,9 +180,12 @@ test("delayed and failed images preserve bottom and reading anchors across remou
       expect(box.height).toBeGreaterThan(0);
     }
   } finally {
-    await release();
-    await page.unrouteAll({ behavior: "wait" });
-    await server.close();
+    try {
+      await release();
+      await page.unrouteAll({ behavior: "wait" });
+    } finally {
+      await server.close();
+    }
   }
 });
 
@@ -314,12 +317,12 @@ async function routeOriginals(page, requests) {
 test("blurhash visibility, decode swap, failure and retired source lifetimes", async ({
   page,
 }, testInfo) => {
-  const server = await fixtureServer();
   const requests = [];
   await holdDecodes(page);
   await routeOriginals(page, requests);
-  await server.listen();
+  const server = await fixtureServer();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/attachment-image.html`,
     );
@@ -402,19 +405,22 @@ test("blurhash visibility, decode swap, failure and retired source lifetimes", a
       contentType: "application/json",
     });
   } finally {
-    await page.unrouteAll({ behavior: "wait" });
-    await server.close();
+    try {
+      await page.unrouteAll({ behavior: "wait" });
+    } finally {
+      await server.close();
+    }
   }
 });
 
 test("original ready first cannot regress on late visibility; missing and invalid hashes still load", async ({
   page,
 }) => {
-  const server = await fixtureServer();
   await holdDecodes(page, true);
   await routeOriginals(page, []);
-  await server.listen();
+  const server = await fixtureServer();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/attachment-image.html`,
     );
@@ -433,19 +439,22 @@ test("original ready first cannot regress on late visibility; missing and invali
       await shown(page);
     }
   } finally {
-    await page.unrouteAll({ behavior: "wait" });
-    await server.close();
+    try {
+      await page.unrouteAll({ behavior: "wait" });
+    } finally {
+      await server.close();
+    }
   }
 });
 
 test("original decode rejection retains blur and the next source still recovers", async ({
   page,
 }) => {
-  const server = await fixtureServer();
   await holdDecodes(page);
   await routeOriginals(page, []);
-  await server.listen();
+  const server = await fixtureServer();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/attachment-image.html`,
     );
@@ -463,8 +472,11 @@ test("original decode rejection retains blur and the next source still recovers"
     await shown(page);
     await expect(frame(page).locator("canvas")).toHaveCount(0);
   } finally {
-    await page.unrouteAll({ behavior: "wait" });
-    await server.close();
+    try {
+      await page.unrouteAll({ behavior: "wait" });
+    } finally {
+      await server.close();
+    }
   }
 });
 
@@ -472,7 +484,6 @@ for (const unavailable of ["canvas", "visibility"]) {
   test(`unavailable ${unavailable} keeps the placeholder and original loading`, async ({
     page,
   }) => {
-    const server = await fixtureServer();
     await holdDecodes(page);
     await page.addInitScript((unavailable) => {
       if (unavailable === "canvas")
@@ -480,8 +491,9 @@ for (const unavailable of ["canvas", "visibility"]) {
       else window.IntersectionObserver = undefined;
     }, unavailable);
     await routeOriginals(page, []);
-    await server.listen();
+    const server = await fixtureServer();
     try {
+      await server.listen();
       await page.goto(
         `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/attachment-image.html`,
       );
@@ -496,8 +508,11 @@ for (const unavailable of ["canvas", "visibility"]) {
       await shown(page);
       await expect(frame(page).locator("canvas")).toHaveCount(0);
     } finally {
-      await page.unrouteAll({ behavior: "wait" });
-      await server.close();
+      try {
+        await page.unrouteAll({ behavior: "wait" });
+      } finally {
+        await server.close();
+      }
     }
   });
 }
diff --git a/tests/browser/mention-edit.spec.mjs b/tests/browser/mention-edit.spec.mjs
index 315205ce..c42fee27 100644
--- a/tests/browser/mention-edit.spec.mjs
+++ b/tests/browser/mention-edit.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 test("editing selected name plus pasting same name cannot transfer notification to pasted prose", async ({
@@ -13,8 +13,8 @@ test("editing selected name plus pasting same name cannot transfer notification
     logLevel: "error",
     server: { host: "127.0.0.1", port: 0 },
   });
-  await server.listen();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/mentions.html`,
     );
diff --git a/tests/browser/mentions.spec.mjs b/tests/browser/mentions.spec.mjs
index 5115d136..fe7cbe1f 100644
--- a/tests/browser/mentions.spec.mjs
+++ b/tests/browser/mentions.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
@@ -16,8 +16,8 @@ test("actual composer selects namesakes by exact key, publishes channel/reply ta
   });
   const errors = [];
   page.on("pageerror", (error) => errors.push(String(error)));
-  await server.listen();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/mentions.html`,
     );
diff --git a/tests/browser/messages.spec.mjs b/tests/browser/messages.spec.mjs
index 99b1c3d1..f95a7aec 100644
--- a/tests/browser/messages.spec.mjs
+++ b/tests/browser/messages.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
@@ -18,8 +18,8 @@ test("shared thread UI auto-loads, follows live replies, retries and isolates re
   });
   const errors = [];
   page.on("pageerror", (error) => errors.push(String(error)));
-  await server.listen();
   try {
+    await server.listen();
     const address = server.httpServer.address();
     await page.goto(
       `http://127.0.0.1:${address.port}/tests/fixtures/messages.html`,
diff --git a/tests/browser/profiles.spec.mjs b/tests/browser/profiles.spec.mjs
index 8a9ea388..e300d21e 100644
--- a/tests/browser/profiles.spec.mjs
+++ b/tests/browser/profiles.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
@@ -16,8 +16,8 @@ test("profile plumbing: exact avatar/mention targets, thread enrichment, lifecyc
   });
   const errors = [];
   page.on("pageerror", (error) => errors.push(String(error)));
-  await server.listen();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/profiles.html`,
     );
@@ -170,8 +170,8 @@ test("contextual panel callbacks retire with opening, channel, contribution and
     logLevel: "error",
     server: { host: "127.0.0.1", port: 0, strictPort: false },
   });
-  await server.listen();
   try {
+    await server.listen();
     await page.goto(
       `http://127.0.0.1:${server.httpServer.address().port}/tests/fixtures/profiles.html?context-probe`,
     );
diff --git a/tests/browser/terminal-renderer.spec.mjs b/tests/browser/terminal-renderer.spec.mjs
index f78d8b9f..db59007a 100644
--- a/tests/browser/terminal-renderer.spec.mjs
+++ b/tests/browser/terminal-renderer.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
diff --git a/tests/browser/typeahead.spec.mjs b/tests/browser/typeahead.spec.mjs
index d0107a59..2bb5651a 100644
--- a/tests/browser/typeahead.spec.mjs
+++ b/tests/browser/typeahead.spec.mjs
@@ -1,5 +1,5 @@
 import { test, expect } from "@playwright/test";
-import { createServer } from "vite";
+import { createServer } from "./vite-server.mjs";
 import react from "@vitejs/plugin-react";
 import { fileURLToPath } from "node:url";
 
diff --git a/tests/browser/vite-server.mjs b/tests/browser/vite-server.mjs
new file mode 100644
index 00000000..48a44872
--- /dev/null
+++ b/tests/browser/vite-server.mjs
@@ -0,0 +1,24 @@
+import { createServer as createViteServer } from "vite";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+// Parallel fixture servers must not invalidate each other's optimized imports.
+export async function createServer(config) {
+  const cacheDir = await mkdtemp(join(tmpdir(), "buzz-fixture-vite-"));
+  try {
+    const server = await createViteServer({ ...config, cacheDir });
+    const close = server.close.bind(server);
+    server.close = async () => {
+      try {
+        await close();
+      } finally {
+        await rm(cacheDir, { recursive: true, force: true });
+      }
+    };
+    return server;
+  } catch (error) {
+    await rm(cacheDir, { recursive: true, force: true });
+    throw error;
+  }
+}
diff --git a/tests/integration/vite-fixture.test.mjs b/tests/integration/vite-fixture.test.mjs
new file mode 100644
index 00000000..0dac1ce0
--- /dev/null
+++ b/tests/integration/vite-fixture.test.mjs
@@ -0,0 +1,74 @@
+import assert from "node:assert/strict";
+import { readFile, readdir, stat, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+import test from "node:test";
+import { createServer } from "../browser/vite-server.mjs";
+
+const root = fileURLToPath(new URL("../../", import.meta.url));
+const config = {
+  root,
+  configFile: false,
+  envDir: false,
+  logLevel: "silent",
+  server: { middlewareMode: true, watch: null },
+  optimizeDeps: { noDiscovery: true, include: [] },
+};
+
+test("concurrent fixture servers own distinct optimizer caches and retire only their own files", async () => {
+  const servers = [];
+  try {
+    servers.push(await createServer(config));
+    servers.push(await createServer(config));
+    const [first, second] = servers;
+    assert.notEqual(first.config.cacheDir, second.config.cacheDir);
+    assert.notEqual(first.config.cacheDir, join(root, "node_modules/.vite"));
+    const retained = join(second.config.cacheDir, "retained-dependency.js");
+    await writeFile(retained, "export default 1;");
+    await first.close();
+    await assert.rejects(stat(first.config.cacheDir), { code: "ENOENT" });
+    assert.equal(await readFile(retained, "utf8"), "export default 1;");
+    await second.close();
+    await assert.rejects(stat(second.config.cacheDir), { code: "ENOENT" });
+  } finally {
+    await Promise.all(servers.map((server) => server.close()));
+  }
+});
+
+test("failed fixture creation cleans its owned cache and preserves the error", async () => {
+  let cacheDir;
+  const failure = new Error("fixture configuration failed");
+  await assert.rejects(
+    createServer({
+      ...config,
+      plugins: [
+        {
+          name: "fail-fixture-configuration",
+          configResolved(resolved) {
+            cacheDir = resolved.cacheDir;
+            throw failure;
+          },
+        },
+      ],
+    }),
+    (error) => error === failure,
+  );
+  assert.ok(cacheDir);
+  await assert.rejects(stat(cacheDir), { code: "ENOENT" });
+});
+
+test("browser fixture call sites cannot fall back to Vite's shared default cache", async () => {
+  const browser = join(root, "tests/browser");
+  for (const name of await readdir(browser)) {
+    if (!name.endsWith(".spec.mjs")) continue;
+    const source = await readFile(join(browser, name), "utf8");
+    if (!source.includes('import { createServer } from "vite"')) continue;
+    // These existing tests own a temporary directory through their full lifecycle.
+    assert.ok(["emoji.spec.mjs", "conversation.spec.mjs"].includes(name), name);
+    assert.match(
+      source,
+      /cacheDir[,:]/,
+      `${name} must keep its explicit cache`,
+    );
+  }
+});