Cap original-detail image token estimates (#19865)

Clamp original-detail image patch estimates to the current 10k patch
budget so large images cannot inflate local context accounting without
bound. Add regression coverage for an over-budget image.

Fixes openai/codex#19806.

codex-rs/core/src/context_manager/history.rs

@@ -519,6 +519,10 @@ const RESIZED_IMAGE_BYTES_ESTIMATE: i64 = 7373;
 // Use a direct 32px patch count only for `detail: "original"`;
 // all other image inputs continue to use `RESIZED_IMAGE_BYTES_ESTIMATE`.
 const ORIGINAL_IMAGE_PATCH_SIZE: u32 = 32;
+// See https://platform.openai.com/docs/guides/images-vision#model-sizing-behavior.
+// Keep this hard-coded for now; move it into model capabilities if the patch
+// budget starts changing often across model releases.
+const ORIGINAL_IMAGE_MAX_PATCHES: usize = 10_000;
 const ORIGINAL_IMAGE_ESTIMATE_CACHE_SIZE: usize = 32;
 
 static ORIGINAL_IMAGE_ESTIMATE_CACHE: LazyLock<BlockingLruCache<[u8; 20], Option<i64>>> =
@@ -621,6 +625,7 @@ fn estimate_original_image_bytes(image_url: &str) -> Option<i64> {
         let patches_high = height.saturating_add(patch_size.saturating_sub(1)) / patch_size;
         let patch_count = patches_wide.saturating_mul(patches_high);
         let patch_count = usize::try_from(patch_count).unwrap_or(usize::MAX);
+        let patch_count = patch_count.min(ORIGINAL_IMAGE_MAX_PATCHES);
         Some(i64::try_from(approx_bytes_for_tokens(patch_count)).unwrap_or(i64::MAX))
     })
 }

codex-rs/core/src/context_manager/history_tests.rs

@@ -26,6 +26,7 @@ use codex_utils_output_truncation::TruncationPolicy;
 use codex_utils_output_truncation::truncate_text;
 use image::ImageBuffer;
 use image::ImageFormat;
+use image::Luma;
 use image::Rgba;
 use pretty_assertions::assert_eq;
 use regex_lite::Regex;
@@ -1900,6 +1901,38 @@ fn original_detail_images_scale_with_dimensions() {
     assert_eq!(estimated, expected);
 }
 
+#[test]
+fn original_detail_images_are_capped_at_max_patch_count() {
+    // 3201x3201 at 32px patches yields 101 * 101 = 10,201 patches,
+    // which exceeds the original-detail patch budget.
+    let width = 3201;
+    let height = 3201;
+    let image = ImageBuffer::from_pixel(width, height, Luma([12u8]));
+    let mut bytes = std::io::Cursor::new(Vec::new());
+    image
+        .write_to(&mut bytes, ImageFormat::Png)
+        .expect("encode png");
+    let payload = BASE64_STANDARD.encode(bytes.get_ref());
+    let image_url = format!("data:image/png;base64,{payload}");
+    let item = ResponseItem::FunctionCallOutput {
+        call_id: "call-original-capped".to_string(),
+        output: FunctionCallOutputPayload::from_content_items(vec![
+            FunctionCallOutputContentItem::InputImage {
+                image_url,
+                detail: Some(ImageDetail::Original),
+            },
+        ]),
+    };
+
+    let raw_len = serde_json::to_string(&item).unwrap().len() as i64;
+    let estimated = estimate_response_item_model_visible_bytes(&item);
+    let capped_original_detail_image_bytes =
+        i64::try_from(approx_bytes_for_tokens(ORIGINAL_IMAGE_MAX_PATCHES)).unwrap();
+    let expected = raw_len - payload.len() as i64 + capped_original_detail_image_bytes;
+
+    assert_eq!(estimated, expected);
+}
+
 #[test]
 fn original_detail_webp_images_scale_with_dimensions() {
     // Same dimensions as the PNG case above, so the patch-based replacement cost is the same.