fix(read): prevent unsupported image formats from being sending to provider (#21114)

Co-authored-by: Aiden Cline <aidenpcline@gmail.com>

packages/opencode/test/tool/read.test.ts

@@ -440,6 +440,24 @@ root_type Monster;`
       expect(result.output).toContain("table Monster")
     }),
   )
+
+  it.live("falls through unsupported image mime types to text", () =>
+    Effect.gen(function* () {
+      const dir = yield* tmpdirScoped()
+      const cases = [
+        ["image.bmp", "BM text content"],
+        ["photo.tiff", "II text content"],
+        ["photo.avif", "avif text content"],
+      ] as const
+
+      for (const item of cases) {
+        yield* put(path.join(dir, item[0]), item[1])
+        const result = yield* exec(dir, { filePath: path.join(dir, item[0]) })
+        expect(result.attachments).toBeUndefined()
+        expect(result.output).toContain(item[1])
+      }
+    }),
+  )
 })
 
 describe("tool.read loaded instructions", () => {