fix(files): keep text opens working after content-cache dispose

React Strict Mode disposed the memoized content-cache owner while the
provider kept reusing it, so validateContextFileOpen threw before any
/api/fs/read and toasted "Failed to open file" for notes.txt. Binaries
still opened because they skip the pre-read. Serve uncached reads from
disposed owners, clear cache on runtime switch without deactivating, and
own the cache lifecycle in an effect.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/contexts/RuntimeAPIProvider.tsx

@@ -1,17 +1,32 @@
 import React, { type JSX, type ReactNode } from 'react';
 import { RuntimeAPIContext } from '@/contexts/runtimeAPIContext';
-import type { RuntimeAPIs } from '@/lib/api/types';
+import type { FilesAPI, RuntimeAPIs } from '@/lib/api/types';
 import { createContentCachedFiles } from '@/contexts/content-cache-owner';
 
+type ContentCachedFiles = ReturnType<typeof createContentCachedFiles>;
+
 export function RuntimeAPIProvider({ apis, children }: { apis: RuntimeAPIs; children: ReactNode }): JSX.Element {
-  const cachedFiles = React.useMemo(() => createContentCachedFiles(apis.files), [apis.files]);
-  React.useEffect(() => () => cachedFiles.dispose(), [cachedFiles]);
+  // Effect-owned lifecycle: React Strict Mode dispose+remount must create a fresh
+  // owner. useMemo + dispose reused a dead owner and broke text-file opens
+  // (binaries skipped the pre-read, so they still appeared to work).
+  const [cachedOwner, setCachedOwner] = React.useState<ContentCachedFiles | null>(null);
+
+  React.useEffect(() => {
+    const owner = createContentCachedFiles(apis.files);
+    setCachedOwner(owner);
+    return () => {
+      owner.dispose();
+      setCachedOwner((current) => (current === owner ? null : current));
+    };
+  }, [apis.files]);
+
+  const files: FilesAPI = cachedOwner?.files ?? apis.files;
   const cachedApis = React.useMemo<RuntimeAPIs>(
     () => ({
       ...apis,
-      files: cachedFiles.files,
+      files,
     }),
-    [apis, cachedFiles],
+    [apis, files],
   );
   return <RuntimeAPIContext.Provider value={cachedApis}>{children}</RuntimeAPIContext.Provider>;
 }

packages/ui/src/contexts/content-cache-owner.test.ts

@@ -71,4 +71,68 @@ describe("content cache owner", () => {
     expect(second.content).toBe("/b-2")
     owner.dispose()
   })
+
+  test("disposed owners still read through without throwing", async () => {
+    let reads = 0
+    const owner = createContentCachedFiles({
+      readFile: async (path: string) => ({ path, content: `value-${++reads}` }),
+      statFile: async () => ({ isFile: true, isDirectory: false, size: 7, mtimeMs: 1 }),
+    } as unknown as FilesAPI)
+
+    owner.dispose()
+    expect((await owner.files.readFile!("notes.txt", { optional: true, directory: "/tmp/project" })).content).toBe("value-1")
+    expect(reads).toBe(1)
+  })
+
+  test("validateContextFileOpen succeeds against a disposed cached files API", async () => {
+    const { validateContextFileOpen } = await import("@/lib/contextFileOpenGuard")
+    const owner = createContentCachedFiles({
+      listDirectory: async () => ({ directory: "/", entries: [] }),
+      readFile: async (path: string) => ({ path, content: "hello from notes\n" }),
+    } as unknown as FilesAPI)
+
+    owner.dispose()
+    expect(await validateContextFileOpen(owner.files, "/tmp/project/notes.txt", { directory: "/tmp/project" })).toEqual({
+      ok: true,
+    })
+  })
+
+  test("runtime endpoint changes clear cache but keep serving reads", async () => {
+    const originalWindow = globalThis.window
+    const events = new EventTarget()
+    Object.defineProperty(globalThis, "window", {
+      configurable: true,
+      value: {
+        addEventListener: events.addEventListener.bind(events),
+        removeEventListener: events.removeEventListener.bind(events),
+        dispatchEvent: events.dispatchEvent.bind(events),
+      },
+    })
+
+    try {
+      let reads = 0
+      const owner = createContentCachedFiles({
+        readFile: async (path: string) => ({ path, content: `value-${++reads}` }),
+        statFile: async () => ({ isFile: true, isDirectory: false, size: 7, mtimeMs: 1 }),
+      } as unknown as FilesAPI)
+
+      expect((await owner.files.readFile!("notes.txt")).content).toBe("value-1")
+      window.dispatchEvent(new CustomEvent("openchamber:runtime-endpoint-will-change", {
+        detail: {
+          apiBaseUrl: "http://127.0.0.1:3902",
+          previousApiBaseUrl: "http://127.0.0.1:3901",
+          runtimeKey: "url:http://127.0.0.1:3902",
+          previousRuntimeKey: "url:http://127.0.0.1:3901",
+        },
+      }))
+      expect((await owner.files.readFile!("notes.txt")).content).toBe("value-2")
+      expect(reads).toBe(2)
+      owner.dispose()
+    } finally {
+      Object.defineProperty(globalThis, "window", {
+        configurable: true,
+        value: originalWindow,
+      })
+    }
+  })
 })

packages/ui/src/contexts/content-cache-owner.ts

@@ -32,6 +32,10 @@ export function createContentCachedFiles(files: FilesAPI): { files: FilesAPI; di
     && cached.mtimeMs === latest.mtimeMs
     && cached.size === latest.size
   );
+  const clearCache = () => {
+    cache.clear();
+    totalBytes = 0;
+  };
   const cacheResult = (
     key: string,
     sourcePath: string,
@@ -61,7 +65,8 @@ export function createContentCachedFiles(files: FilesAPI): { files: FilesAPI; di
     const before = await files.statFile?.(path, options).catch(() => null);
     const result = await files.readFile!(path, options);
     const after = await files.statFile?.(path, options).catch(() => null);
-    if (!active) throw new Error('File read invalidated by runtime change');
+    // Disposed mid-read: still return the bytes we fetched; do not cache.
+    if (!active) return result;
     if (capturedGeneration !== generation) return cachedReadFile!(path, options);
     const stable = before && after && before.isFile && after.isFile
       && before.mtimeMs !== undefined && after.mtimeMs !== undefined
@@ -72,14 +77,17 @@ export function createContentCachedFiles(files: FilesAPI): { files: FilesAPI; di
   const cachedReadFile: FilesAPI['readFile'] = files.readFile
     ? async (path, options) => {
         await mutationBarrier;
-        if (!active) throw new Error('File cache owner disposed');
+        // Disposed owners must keep serving reads. React Strict Mode can dispose a
+        // memoized owner that the provider still holds; throwing here surfaces as
+        // "Failed to open file" with no /api/fs/read request for text opens.
+        if (!active) return files.readFile!(path, options);
         const capturedGeneration = generation;
         if (options?.allowOutsideWorkspace) return files.readFile!(path, options);
         const key = cacheKey(path, options);
         const hit = cache.get(key);
         if (!hit) return readFresh(key, path, options, capturedGeneration);
         const latest = await files.statFile?.(path, options).catch(() => null);
-        if (!active) throw new Error('File read invalidated by runtime change');
+        if (!active) return files.readFile!(path, options);
         if (capturedGeneration !== generation) return cachedReadFile!(path, options);
         if (!latest || !metadataMatches(hit, latest)) {
           removeEntry(key);
@@ -116,18 +124,18 @@ export function createContentCachedFiles(files: FilesAPI): { files: FilesAPI; di
   };
   const unsubscribeRuntime = subscribeRuntimeEndpointWillChange((detail) => {
     if (detail.runtimeKey === detail.previousRuntimeKey) return;
-    active = false;
+    // Invalidate cached content for the previous runtime, but keep serving reads.
+    // `apis.files` is typically stable across endpoint switches, so permanently
+    // deactivating this owner would break every subsequent text-file open.
     generation += 1;
-    cache.clear();
-    totalBytes = 0;
+    clearCache();
   });
   return {
     files: cachedFiles,
     dispose: () => {
       active = false;
       generation += 1;
-      cache.clear();
-      totalBytes = 0;
+      clearCache();
       unsubscribeRuntime();
     },
   };