diff --git a/packages/studio-server/src/routes/preview.test.ts b/packages/studio-server/src/routes/preview.test.ts
index 753cb0b8d6..8b5f779dd9 100644
--- a/packages/studio-server/src/routes/preview.test.ts
+++ b/packages/studio-server/src/routes/preview.test.ts
@@ -116,6 +116,34 @@ describe("registerPreviewRoutes", () => {
     expect(authored).not.toContain('<base href="/api/projects/demo/preview/">');
   });
 
+  it("encodes the project name in <base>, so a '#' or '\"' in it keeps assets in its own folder", async () => {
+    const projectDir = createProjectDir();
+    writeFileSync(join(projectDir, "scene.html"), "<template><section></section></template>");
+    const app = new Hono();
+    registerPreviewRoutes(app, createAdapter(projectDir));
+    const baseOf = async (path: string) =>
+      /<base href="([^"]*)">/.exec(
+        await (await app.request(`http://localhost${path}`)).text(),
+      )?.[1];
+    const take = "/api/projects/Take%20%232/preview/";
+    expect(await baseOf("/projects/Take%20%232/preview")).toBe(take);
+    expect(await baseOf("/projects/Take%20%232/preview/comp/scene.html")).toBe(take);
+    expect(new URL("logo.png", `http://localhost${take}`).pathname).toBe(`${take}logo.png`);
+    expect(await baseOf("/projects/a%22b/preview")).toBe("/api/projects/a%22b/preview/");
+  });
+
+  it("keeps the encoded <base> when the bundler fails and the page is read from disk", async () => {
+    const projectDir = createProjectDir();
+    const app = new Hono();
+    const bundle = async () => {
+      throw new Error("bundler unavailable");
+    };
+    registerPreviewRoutes(app, createAdapter(projectDir, { bundle }));
+    writeFileSync(join(projectDir, "index.html"), '<html><head data-theme="dark"></head></html>');
+    const html = await (await app.request("http://localhost/projects/Take%20%232/preview")).text();
+    expect(html).toContain('<base href="/api/projects/Take%20%232/preview/">');
+  });
+
   it("serves the mark the runtime keys preview-only work on, ahead of the runtime script", async () => {
     const projectDir = createProjectDir();
     const app = new Hono();
diff --git a/packages/studio-server/src/routes/preview.ts b/packages/studio-server/src/routes/preview.ts
index 7fd3d460cd..1d20ced7fb 100644
--- a/packages/studio-server/src/routes/preview.ts
+++ b/packages/studio-server/src/routes/preview.ts
@@ -344,6 +344,14 @@ export const PREVIEW_BUNDLE_OPTIONS = {
   sceneParts: true,
 } as const satisfies BundleOptions;
 
+const previewBaseHref = (projectId: string) =>
+  `/api/projects/${encodeURIComponent(projectId)}/preview/`;
+
+const withPreviewBase = (html: string, projectId: string) =>
+  hasBaseElement(html)
+    ? html
+    : injectTagsAtHeadStart(html, `<base href="${previewBaseHref(projectId)}">`);
+
 export function registerPreviewRoutes(api: Hono, adapter: PreviewApiAdapter): void {
   const previewCacheHeaders = (etag: string) => ({
     "Cache-Control": "private, no-cache",
@@ -406,10 +414,7 @@ export function registerPreviewRoutes(api: Hono, adapter: PreviewApiAdapter): vo
       }
 
       // Inject <base> for relative asset resolution
-      const baseHref = `/api/projects/${project.id}/preview/`;
-      if (!hasBaseElement(bundled)) {
-        bundled = bundled.replace(/<head>/i, `<head><base href="${baseHref}">`);
-      }
+      bundled = withPreviewBase(bundled, project.id);
 
       // Also covers elements the adapter injected; ids already present are kept.
       bundled = injectStudioPreviewAugmentations(
@@ -438,7 +443,7 @@ export function registerPreviewRoutes(api: Hono, adapter: PreviewApiAdapter): vo
       // not the pre-request snapshot that may have been saved over.
       const fallback = resolveProjectMainHtml(project.dir, project.id);
       if (fallback) {
-        const fallbackHtml = ensureHfIds(fallback.html);
+        const fallbackHtml = withPreviewBase(ensureHfIds(fallback.html), project.id);
         let fallbackAugmented = injectStudioPreviewAugmentations(
           await transformPreviewHtml(fallbackHtml, adapter, project, fallback.compositionPath),
           adapter,
@@ -549,7 +554,7 @@ export function registerPreviewRoutes(api: Hono, adapter: PreviewApiAdapter): vo
     const stamped = pinSubCompHfIds(compFile, compPath);
     if (stamped === null) return c.text("not found", 404); // file removed between stat and read
 
-    const baseHref = `/api/projects/${project.id}/preview/`;
+    const baseHref = previewBaseHref(project.id);
     let html = buildSubCompositionHtml(
       project.dir,
       compPath,
diff --git a/packages/studio/src/components/editor/useColorGradingController.test.ts b/packages/studio/src/components/editor/useColorGradingController.test.ts
index d86796dbde..61baabe6fd 100644
--- a/packages/studio/src/components/editor/useColorGradingController.test.ts
+++ b/packages/studio/src/components/editor/useColorGradingController.test.ts
@@ -71,7 +71,9 @@ function HookHost({
   element,
   previewIframeRef,
   onApplyScope,
+  projectId = "proj",
 }: {
+  projectId?: string;
   onState: (state: ReturnType<typeof useColorGradingController>) => void;
   onSetAttributeLive: (attr: string, value: string | null) => void;
   element: DomEditSelection;
@@ -79,7 +81,7 @@ function HookHost({
   onApplyScope?: ApplyScope;
 }) {
   const state = useColorGradingController({
-    projectId: "proj",
+    projectId,
     element,
     previewIframeRef,
     onSetAttributeLive,
@@ -94,6 +96,7 @@ function renderHook(
   initialElement: DomEditSelection = makeElement(),
   previewIframeRef?: React.RefObject<HTMLIFrameElement | null>,
   onApplyScope?: ApplyScope,
+  projectId?: string,
 ) {
   const host = document.createElement("div");
   document.body.append(host);
@@ -108,6 +111,7 @@ function renderHook(
           element,
           previewIframeRef,
           onApplyScope,
+          projectId,
         }),
       );
     });
@@ -763,6 +767,37 @@ describe("useColorGradingController", () => {
     act(() => second.root.unmount());
     vi.unstubAllGlobals();
   });
+
+  it("keeps media metadata apart for 'p:a' + 'b.mp4' and 'p' + 'a:b.mp4'", async () => {
+    const video = (src: string) => {
+      const el = document.createElement("video");
+      el.setAttribute("src", src);
+      return el;
+    };
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ metadata: { kind: "video", color: { dynamicRange: "hdr" } } }),
+    } as unknown as Response);
+    vi.stubGlobal("fetch", fetchMock);
+    for (const [projectId, src] of [
+      ["p:a", "b.mp4"],
+      ["p", "a:b.mp4"],
+    ]) {
+      const { root } = renderHook(
+        vi.fn(),
+        makeElement({ element: video(src) }),
+        undefined,
+        undefined,
+        projectId,
+      );
+      await act(async () => {
+        await Promise.resolve();
+      });
+      act(() => root.unmount());
+    }
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    vi.unstubAllGlobals();
+  });
 });
 
 describe("useColorGradingController after the preview iframe is replaced", () => {
diff --git a/packages/studio/src/components/editor/useColorGradingController.ts b/packages/studio/src/components/editor/useColorGradingController.ts
index 3d69c99250..b1a30f2975 100644
--- a/packages/studio/src/components/editor/useColorGradingController.ts
+++ b/packages/studio/src/components/editor/useColorGradingController.ts
@@ -284,13 +284,13 @@ export function useColorGradingController({
   useEffect(() => {
     setMediaMetadata(null);
     if (!selectedAssetPath) return;
-    const cacheKey = `${projectId}:${selectedAssetPath}`;
+    const cacheKey = mediaMetadataUrl(projectId, selectedAssetPath);
     if (MEDIA_METADATA_CACHE.has(cacheKey)) {
       setMediaMetadata(MEDIA_METADATA_CACHE.get(cacheKey) ?? null);
       return;
     }
     const controller = new AbortController();
-    fetch(mediaMetadataUrl(projectId, selectedAssetPath), { signal: controller.signal })
+    fetch(cacheKey, { signal: controller.signal })
       .then(async (response) => {
         if (!response.ok) return { ok: false as const };
         const data: MediaMetadataResponse | null = await response.json();
diff --git a/packages/studio/src/utils/projectRouting.test.ts b/packages/studio/src/utils/projectRouting.test.ts
index 9f022719e3..4f62929c90 100644
--- a/packages/studio/src/utils/projectRouting.test.ts
+++ b/packages/studio/src/utils/projectRouting.test.ts
@@ -18,6 +18,15 @@ describe("project routing utilities", () => {
     },
   );
 
+  it("opens a folder whose name has a colon, encoded once both ways", () => {
+    const id = "Customer story: Northwind";
+    expect(encodeProjectId(id)).toBe("Customer%20story%3A%20Northwind");
+    expect(buildProjectApiPath(id, "/preview")).toBe(
+      "/api/projects/Customer%20story%3A%20Northwind/preview",
+    );
+    expect(parseProjectIdFromHash(buildProjectHash(id))).toBe(id);
+  });
+
   it("decodes project ids from hash routes before building capture URLs", () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-05-01T12:00:00Z"));
diff --git a/packages/studio/src/utils/projectRouting.ts b/packages/studio/src/utils/projectRouting.ts
index 6291d665c8..1b991beecc 100644
--- a/packages/studio/src/utils/projectRouting.ts
+++ b/packages/studio/src/utils/projectRouting.ts
@@ -5,13 +5,15 @@ export interface ProjectHashRoute {
   params: URLSearchParams;
 }
 
+const WINDOWS_DRIVE_PREFIX = /^[a-z]:/i;
+
 /** Project names are single path segments, including when received from a hash or server. */
 export function isValidProjectId(value: string): boolean {
   return (
     value.length > 0 &&
     value !== "." &&
     value !== ".." &&
-    !value.includes(":") &&
+    !WINDOWS_DRIVE_PREFIX.test(value) &&
     !value.includes("/") &&
     !value.includes("\\") &&
     !Array.from(value).some((char) => char.charCodeAt(0) < 32)
diff --git a/packages/studio/vite.adapter.projects.test.ts b/packages/studio/vite.adapter.projects.test.ts
index 2f844da539..ecf3574344 100644
--- a/packages/studio/vite.adapter.projects.test.ts
+++ b/packages/studio/vite.adapter.projects.test.ts
@@ -171,6 +171,31 @@ describe("Vite project resolution boundary", () => {
     },
   );
 
+  it("opens a folder named with a colon, which Windows would read as a file stream and refuses", () => {
+    const { data, sessions, adapter } = fixture();
+    const id = "Customer story: Northwind";
+    mkdirSync(join(data, "demo"));
+    if (process.platform !== "win32") {
+      mkdirSync(join(data, id));
+      expect(adapter.resolveProject(id)?.id).toBe(id);
+    }
+    writeFileSync(join(sessions, "alias.json"), JSON.stringify({ projectId: id }));
+    writeFileSync(
+      join(sessions, "stream.json"),
+      JSON.stringify({ projectId: "demo::$INDEX_ALLOCATION" }),
+    );
+    const platform = Object.getOwnPropertyDescriptor(process, "platform")!;
+    Object.defineProperty(process, "platform", { value: "win32" });
+    try {
+      expect(adapter.resolveProject(id)).toBeNull();
+      expect(adapter.resolveProject("demo::$INDEX_ALLOCATION")).toBeNull();
+      expect(adapter.resolveProject("alias")).toBeNull();
+      expect(adapter.resolveProject("stream")).toBeNull();
+    } finally {
+      Object.defineProperty(process, "platform", platform);
+    }
+  });
+
   it("rejects traversal in a session's project mapping", () => {
     const { sessions, adapter } = fixture();
     writeFileSync(join(sessions, "alias.json"), JSON.stringify({ projectId: "../sessions" }));
diff --git a/packages/studio/vite.adapter.ts b/packages/studio/vite.adapter.ts
index b99a69970e..939f33aec7 100644
--- a/packages/studio/vite.adapter.ts
+++ b/packages/studio/vite.adapter.ts
@@ -102,6 +102,9 @@ export function createProjectSignatureCache({
   };
 }
 
+const isServableProjectId = (id: string) =>
+  isValidProjectId(id) && !(process.platform === "win32" && id.includes(":"));
+
 export function createViteAdapter(
   dataDir: string,
   server: ViteDevServer,
@@ -208,7 +211,7 @@ export function createViteAdapter(
       return readdirSync(dataDir, { withFileTypes: true })
         .filter(
           (d) =>
-            isValidProjectId(d.name) &&
+            isServableProjectId(d.name) &&
             (d.isDirectory() || d.isSymbolicLink()) &&
             (existsSync(join(dataDir, d.name, "index.html")) ||
               existsSync(join(dataDir, d.name, `${d.name}.html`))),
@@ -233,7 +236,7 @@ export function createViteAdapter(
 
     // fallow-ignore-next-line complexity
     resolveProject(id: string) {
-      if (!isValidProjectId(id)) return null;
+      if (!isServableProjectId(id)) return null;
       let projectDir = resolve(dataDir, id);
       if (!isPathWithin(dataDir, projectDir)) return null;
       if (!existsSync(projectDir)) {
@@ -243,7 +246,7 @@ export function createViteAdapter(
         if (existsSync(sessionFile)) {
           try {
             const session = JSON.parse(readFileSync(sessionFile, "utf-8"));
-            if (typeof session.projectId === "string" && isValidProjectId(session.projectId)) {
+            if (typeof session.projectId === "string" && isServableProjectId(session.projectId)) {
               projectDir = resolve(dataDir, session.projectId);
               if (!isPathWithin(dataDir, projectDir)) return null;
               if (existsSync(projectDir)) {