feat: normalize and filter chat attachments

Attachment pickers now share an allowlist for supported file types
Local attachments are normalized to consistent MIME types before upload
VS Code file picker now respects extension filters and larger files are allowed

packages/ui/src/sync/input-store.test.ts

@@ -135,4 +135,81 @@ describe("input-store attachments", () => {
 
     expect(useInputStore.getState().attachedFiles.map((attached) => attached.filename)).toEqual(["hello.txt"])
   })
+
+  testWithMockFileReader("normalizes code files to text/plain", async () => {
+    const addPromise = useInputStore.getState().addAttachedFile(
+      new File(["const value = 1"], "example.ts", { type: "text/typescript" })
+    )
+    expect(pendingReaders).toHaveLength(1)
+
+    resolveReader(pendingReaders[0], "data:text/typescript;base64,Y29uc3QgdmFsdWUgPSAx")
+
+    expect(await addPromise).toBe(true)
+    expect(useInputStore.getState().attachedFiles[0]?.filename).toBe("example.ts")
+    expect(useInputStore.getState().attachedFiles[0]?.mimeType).toBe("text/plain")
+    expect(useInputStore.getState().attachedFiles[0]?.dataUrl).toBe(
+      "data:text/plain;base64,Y29uc3QgdmFsdWUgPSAx"
+    )
+  })
+
+  testWithMockFileReader("normalizes structured text MIME types to text/plain", async () => {
+    const addPromise = useInputStore.getState().addAttachedFile(
+      new File(["{}"], "example.json", { type: "application/json" })
+    )
+    expect(pendingReaders).toHaveLength(1)
+
+    resolveReader(pendingReaders[0], "data:application/json;base64,e30=")
+
+    expect(await addPromise).toBe(true)
+    expect(useInputStore.getState().attachedFiles[0]?.mimeType).toBe("text/plain")
+    expect(useInputStore.getState().attachedFiles[0]?.dataUrl).toBe("data:text/plain;base64,e30=")
+  })
+
+  test("rejects an unknown binary file after inspecting its contents", async () => {
+    const attached = await useInputStore.getState().addAttachedFile(
+      new File([new Uint8Array([0, 1, 2, 3])], "archive.bin", { type: "application/octet-stream" })
+    )
+
+    expect(attached).toBe(false)
+    expect(pendingReaders).toHaveLength(0)
+    expect(useInputStore.getState().attachedFiles).toEqual([])
+  })
+
+  test("rejects unknown content with too many control bytes", async () => {
+    const attached = await useInputStore.getState().addAttachedFile(
+      new File([new Uint8Array([1, 2, 3, 65])], "encoded.custom", { type: "application/octet-stream" })
+    )
+
+    expect(attached).toBe(false)
+    expect(pendingReaders).toHaveLength(0)
+  })
+
+  testWithMockFileReader("accepts an unknown MIME type when its contents are text", async () => {
+    const addPromise = useInputStore.getState().addAttachedFile(
+      new File(["custom text"], "example.custom", { type: "application/octet-stream" })
+    )
+    await new Promise((resolve) => setTimeout(resolve, 0))
+    expect(pendingReaders).toHaveLength(1)
+
+    resolveReader(pendingReaders[0], "data:application/octet-stream;base64,Y3VzdG9tIHRleHQ=")
+
+    expect(await addPromise).toBe(true)
+    expect(useInputStore.getState().attachedFiles[0]?.mimeType).toBe("text/plain")
+    expect(useInputStore.getState().attachedFiles[0]?.dataUrl).toBe(
+      "data:text/plain;base64,Y3VzdG9tIHRleHQ="
+    )
+  })
+
+  testWithMockFileReader("preserves supported image MIME types", async () => {
+    const addPromise = useInputStore.getState().addAttachedFile(
+      new File([new Uint8Array([1, 2, 3])], "image.webp", { type: "image/webp" })
+    )
+    expect(pendingReaders).toHaveLength(1)
+
+    resolveReader(pendingReaders[0], "data:image/webp;base64,AQID")
+
+    expect(await addPromise).toBe(true)
+    expect(useInputStore.getState().attachedFiles[0]?.mimeType).toBe("image/webp")
+    expect(useInputStore.getState().attachedFiles[0]?.dataUrl).toBe("data:image/webp;base64,AQID")
+  })
 })