From d5ea8c71767ef90f4db9ffa3085b9c56afa9e3aa Mon Sep 17 00:00:00 2001
From: Simo Lin <linsimo.mark@gmail.com>
Date: Tue, 2 Dec 2025 19:41:40 -0800
Subject: [PATCH] [model-gateway] multimodality initialization (#13350)

---
 sgl-router/Cargo.toml                       |   9 +-
 sgl-router/src/lib.rs                       |   1 +
 sgl-router/src/multimodal/error.rs          |  47 ++
 sgl-router/src/multimodal/media.rs          | 206 +++++++++
 sgl-router/src/multimodal/mod.rs            |  11 +
 sgl-router/src/multimodal/registry.rs       | 461 ++++++++++++++++++++
 sgl-router/src/multimodal/tracker.rs        | 176 ++++++++
 sgl-router/src/multimodal/types.rs          | 290 ++++++++++++
 sgl-router/tests/multimodal_tracker_test.rs | 151 +++++++
 9 files changed, 1351 insertions(+), 1 deletion(-)
 create mode 100644 sgl-router/src/multimodal/error.rs
 create mode 100644 sgl-router/src/multimodal/media.rs
 create mode 100644 sgl-router/src/multimodal/mod.rs
 create mode 100644 sgl-router/src/multimodal/registry.rs
 create mode 100644 sgl-router/src/multimodal/tracker.rs
 create mode 100644 sgl-router/src/multimodal/types.rs
 create mode 100644 sgl-router/tests/multimodal_tracker_test.rs

diff --git a/sgl-router/Cargo.toml b/sgl-router/Cargo.toml
index 45db679e2..4c786c21a 100644
--- a/sgl-router/Cargo.toml
+++ b/sgl-router/Cargo.toml
@@ -4,7 +4,10 @@ version = "0.2.3"
 edition = "2021"
 
 [features]
-default = []
+default = ["grpc-client"]
+grpc-client = []
+grpc-server = []
+
 vendored-openssl = ["openssl/vendored"]
 
 [lints.rust]
@@ -36,6 +39,7 @@ serde_json = { version = "1.0", default-features = false, features = [
     "std",
     "preserve_order",
 ] }
+serde_bytes = "0.11"
 bytes = "1.8.0"
 rand = "0.9.2"
 reqwest = { version = "0.12.8", features = ["stream", "blocking", "json", "rustls-tls"], default-features = false }
@@ -86,6 +90,9 @@ oracle = { version = "0.6.3", features = ["chrono"] }
 subtle = "2.6"
 rustpython-parser = "0.4.0"
 num-traits = "0.2"
+image = { version = "0.25.4", default-features = false, features = ["png", "jpeg", "gif", "bmp", "ico", "tiff", "webp"] }
+ndarray = "0.16"
+base64 = "0.22"
 openai-harmony = { git = "https://github.com/openai/harmony", tag = "v0.0.4" }
 openmetrics-parser = "0.4.4"
 
diff --git a/sgl-router/src/lib.rs b/sgl-router/src/lib.rs
index c22064586..1b0fe03b9 100644
--- a/sgl-router/src/lib.rs
+++ b/sgl-router/src/lib.rs
@@ -8,6 +8,7 @@ pub mod grpc_client;
 pub mod mcp;
 pub mod metrics;
 pub mod middleware;
+pub mod multimodal;
 pub mod policies;
 pub mod protocols;
 pub mod reasoning_parser;
diff --git a/sgl-router/src/multimodal/error.rs b/sgl-router/src/multimodal/error.rs
new file mode 100644
index 000000000..0d73d3c3d
--- /dev/null
+++ b/sgl-router/src/multimodal/error.rs
@@ -0,0 +1,47 @@
+use std::time::Duration;
+
+use thiserror::Error;
+
+use super::types::Modality;
+
+pub type MultiModalResult<T> = Result<T, MultiModalError>;
+
+#[derive(Debug, Error)]
+pub enum MediaConnectorError {
+    #[error("unsupported media scheme: {0}")]
+    UnsupportedScheme(String),
+    #[error("invalid media URL: {0}")]
+    InvalidUrl(String),
+    #[error("media domain '{0}' is not in the allow list")]
+    DisallowedDomain(String),
+    #[error("local media path is not allowed: {0}")]
+    DisallowedLocalPath(String),
+    #[error("HTTP error while fetching media: {0}")]
+    Http(#[from] reqwest::Error),
+    #[error("I/O error while reading media: {0}")]
+    Io(#[from] std::io::Error),
+    #[error("base64 decode error: {0}")]
+    Base64Decode(#[from] base64::DecodeError),
+    #[error("data URL parse error: {0}")]
+    DataUrl(String),
+    #[error("media decode task failed: {0}")]
+    Blocking(#[from] tokio::task::JoinError),
+    #[error("image decode error: {0}")]
+    Image(#[from] image::ImageError),
+    #[error("media fetch timed out after {0:?}")]
+    Timeout(Duration),
+}
+
+#[derive(Debug, Error)]
+pub enum MultiModalError {
+    #[error(transparent)]
+    Media(#[from] MediaConnectorError),
+    #[error("unsupported content part: {0}")]
+    UnsupportedContent(&'static str),
+    #[error("too many {modality:?} items provided. limit={limit}")]
+    ModalityLimit { modality: Modality, limit: usize },
+    #[error("tracker task join error: {0}")]
+    Join(#[from] tokio::task::JoinError),
+    #[error("tracker validation error: {0}")]
+    Validation(String),
+}
diff --git a/sgl-router/src/multimodal/media.rs b/sgl-router/src/multimodal/media.rs
new file mode 100644
index 000000000..d44633128
--- /dev/null
+++ b/sgl-router/src/multimodal/media.rs
@@ -0,0 +1,206 @@
+use std::{collections::HashSet, path::PathBuf, sync::Arc, time::Duration};
+
+use base64::{engine::general_purpose::STANDARD as BASE64_STANDARD, Engine};
+use bytes::Bytes;
+use image::DynamicImage;
+use reqwest::Client;
+use tokio::{fs, task};
+use url::Url;
+
+use super::{
+    error::MediaConnectorError,
+    types::{ImageDetail, ImageFrame, ImageSource},
+};
+
+#[derive(Clone)]
+pub struct MediaConnectorConfig {
+    pub allowed_domains: Option<Vec<String>>,
+    pub allowed_local_media_path: Option<PathBuf>,
+    pub fetch_timeout: Duration,
+}
+
+impl Default for MediaConnectorConfig {
+    fn default() -> Self {
+        Self {
+            allowed_domains: None,
+            allowed_local_media_path: None,
+            fetch_timeout: Duration::from_secs(10),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct ImageFetchConfig {
+    pub detail: ImageDetail,
+}
+
+impl Default for ImageFetchConfig {
+    fn default() -> Self {
+        Self {
+            detail: ImageDetail::Auto,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub enum MediaSource {
+    Url(String),
+    DataUrl(String),
+    InlineBytes(Vec<u8>),
+    File(PathBuf),
+}
+
+#[derive(Clone)]
+pub struct MediaConnector {
+    client: Client,
+    allowed_domains: Option<HashSet<String>>,
+    allowed_local_media_path: Option<PathBuf>,
+    fetch_timeout: Duration,
+}
+
+impl MediaConnector {
+    pub fn new(client: Client, config: MediaConnectorConfig) -> Result<Self, MediaConnectorError> {
+        let allowed_domains = config.allowed_domains.map(|domains| {
+            domains
+                .into_iter()
+                .map(|d| d.to_ascii_lowercase())
+                .collect::<HashSet<_>>()
+        });
+
+        let allowed_local_media_path = if let Some(path) = config.allowed_local_media_path {
+            Some(std::fs::canonicalize(path)?)
+        } else {
+            None
+        };
+
+        Ok(Self {
+            client,
+            allowed_domains,
+            allowed_local_media_path,
+            fetch_timeout: config.fetch_timeout,
+        })
+    }
+
+    pub async fn fetch_image(
+        &self,
+        source: MediaSource,
+        cfg: ImageFetchConfig,
+    ) -> Result<Arc<ImageFrame>, MediaConnectorError> {
+        match source {
+            MediaSource::Url(url) => self.fetch_http_image(url, cfg).await,
+            MediaSource::DataUrl(data_url) => self.fetch_data_url(data_url, cfg).await,
+            MediaSource::InlineBytes(bytes) => {
+                self.decode_image(bytes.into(), cfg.detail, ImageSource::InlineBytes)
+                    .await
+            }
+            MediaSource::File(path) => self.fetch_file(path, cfg).await,
+        }
+    }
+
+    async fn fetch_http_image(
+        &self,
+        url: String,
+        cfg: ImageFetchConfig,
+    ) -> Result<Arc<ImageFrame>, MediaConnectorError> {
+        let parsed = Url::parse(&url).map_err(|_| MediaConnectorError::InvalidUrl(url.clone()))?;
+        self.ensure_domain_allowed(&parsed)?;
+
+        let mut req = self.client.get(parsed.as_str());
+        if self.fetch_timeout > Duration::ZERO {
+            req = req.timeout(self.fetch_timeout);
+        }
+
+        let resp = req.send().await.map_err(|err| {
+            if err.is_timeout() {
+                MediaConnectorError::Timeout(self.fetch_timeout)
+            } else {
+                MediaConnectorError::Http(err)
+            }
+        })?;
+
+        let resp = resp.error_for_status()?;
+        let bytes = resp.bytes().await?;
+        self.decode_image(
+            bytes,
+            cfg.detail,
+            ImageSource::Url {
+                url: parsed.to_string(),
+            },
+        )
+        .await
+    }
+
+    async fn fetch_data_url(
+        &self,
+        data_url: String,
+        cfg: ImageFetchConfig,
+    ) -> Result<Arc<ImageFrame>, MediaConnectorError> {
+        let (metadata, data) = data_url
+            .split_once(',')
+            .ok_or_else(|| MediaConnectorError::DataUrl("missing comma in data url".into()))?;
+
+        if !metadata.ends_with(";base64") {
+            return Err(MediaConnectorError::DataUrl(
+                "only base64 encoded data URLs are supported".into(),
+            ));
+        }
+
+        let data = data.trim();
+        let decoded = BASE64_STANDARD.decode(data)?;
+        self.decode_image(decoded.into(), cfg.detail, ImageSource::DataUrl)
+            .await
+    }
+
+    async fn fetch_file(
+        &self,
+        path: PathBuf,
+        cfg: ImageFetchConfig,
+    ) -> Result<Arc<ImageFrame>, MediaConnectorError> {
+        let allowed_root = self
+            .allowed_local_media_path
+            .as_ref()
+            .ok_or_else(|| MediaConnectorError::DisallowedLocalPath(path.display().to_string()))?;
+
+        let canonical = fs::canonicalize(&path).await?;
+        if !canonical.starts_with(allowed_root) {
+            return Err(MediaConnectorError::DisallowedLocalPath(
+                path.display().to_string(),
+            ));
+        }
+
+        let bytes = fs::read(&canonical).await?;
+        self.decode_image(
+            bytes.into(),
+            cfg.detail,
+            ImageSource::File { path: canonical },
+        )
+        .await
+    }
+
+    fn ensure_domain_allowed(&self, url: &Url) -> Result<(), MediaConnectorError> {
+        if let Some(allowed) = &self.allowed_domains {
+            let host = url
+                .host_str()
+                .map(|h| h.to_ascii_lowercase())
+                .ok_or_else(|| MediaConnectorError::InvalidUrl(url.to_string()))?;
+            if !allowed.contains(&host) {
+                return Err(MediaConnectorError::DisallowedDomain(host));
+            }
+        }
+        Ok(())
+    }
+
+    async fn decode_image(
+        &self,
+        bytes: Bytes,
+        detail: ImageDetail,
+        source: ImageSource,
+    ) -> Result<Arc<ImageFrame>, MediaConnectorError> {
+        let raw: Arc<Vec<u8>> = Arc::new(bytes.to_vec());
+        let raw_clone = raw.clone();
+        let image: DynamicImage =
+            task::spawn_blocking(move || image::load_from_memory(&raw_clone)).await??;
+
+        Ok(Arc::new(ImageFrame::new(image, raw, detail, source)))
+    }
+}
diff --git a/sgl-router/src/multimodal/mod.rs b/sgl-router/src/multimodal/mod.rs
new file mode 100644
index 000000000..76ee5d1c6
--- /dev/null
+++ b/sgl-router/src/multimodal/mod.rs
@@ -0,0 +1,11 @@
+pub mod error;
+pub mod media;
+pub mod registry;
+pub mod tracker;
+pub mod types;
+
+pub use error::{MediaConnectorError, MultiModalError, MultiModalResult};
+pub use media::{ImageFetchConfig, MediaConnector, MediaConnectorConfig, MediaSource};
+pub use registry::{ModelProcessorSpec, ModelRegistry};
+pub use tracker::{AsyncMultiModalTracker, TrackerConfig, TrackerOutput};
+pub use types::*;
diff --git a/sgl-router/src/multimodal/registry.rs b/sgl-router/src/multimodal/registry.rs
new file mode 100644
index 000000000..eb5c30d33
--- /dev/null
+++ b/sgl-router/src/multimodal/registry.rs
@@ -0,0 +1,461 @@
+use std::collections::HashMap;
+
+use once_cell::sync::Lazy;
+use serde_json::{json, Value};
+use thiserror::Error;
+
+use super::types::{ImageSize, Modality, PromptReplacement, TokenId};
+use crate::tokenizer::traits::Tokenizer as TokenizerTrait;
+
+#[derive(Debug, Error)]
+pub enum ModelRegistryError {
+    #[error("unsupported model: {0}")]
+    UnsupportedModel(String),
+    #[error("token '{token}' not found in tokenizer vocabulary")]
+    TokenNotFound { token: String },
+    #[error("missing config field '{field}'")]
+    MissingConfigField { field: String },
+}
+
+pub type RegistryResult<T> = Result<T, ModelRegistryError>;
+
+/// Metadata about the current model used to derive tokenizer/config dependent fields.
+pub struct ModelMetadata<'a> {
+    pub model_id: &'a str,
+    pub tokenizer: &'a dyn TokenizerTrait,
+    pub config: &'a Value,
+}
+
+impl<'a> ModelMetadata<'a> {
+    pub fn token_id(&self, token: &str) -> RegistryResult<TokenId> {
+        self.tokenizer
+            .token_to_id(token)
+            .map(|id| id as TokenId)
+            .ok_or_else(|| ModelRegistryError::TokenNotFound {
+                token: token.to_string(),
+            })
+    }
+
+    pub fn config_u32(&self, path: &[&str]) -> Option<u32> {
+        Self::find_value(self.config, path).and_then(|value| value.as_u64().map(|v| v as u32))
+    }
+
+    fn find_value<'v>(value: &'v Value, path: &[&str]) -> Option<&'v Value> {
+        let mut current = value;
+        for key in path {
+            current = current.get(*key)?;
+        }
+        Some(current)
+    }
+}
+
+pub trait ModelProcessorSpec: Send + Sync {
+    fn name(&self) -> &'static str;
+    fn matches(&self, metadata: &ModelMetadata) -> bool;
+    fn placeholder_token(&self, metadata: &ModelMetadata) -> RegistryResult<String>;
+    fn placeholder_token_id(&self, metadata: &ModelMetadata) -> RegistryResult<TokenId>;
+    fn modality_limits(&self, metadata: &ModelMetadata)
+        -> RegistryResult<HashMap<Modality, usize>>;
+    fn processor_kwargs(&self, metadata: &ModelMetadata) -> RegistryResult<Value>;
+    fn prompt_replacements(
+        &self,
+        metadata: &ModelMetadata,
+        image_sizes: &[ImageSize],
+    ) -> RegistryResult<Vec<PromptReplacement>>;
+}
+
+pub struct ModelRegistry {
+    specs: Vec<LazySpec>,
+}
+
+impl ModelRegistry {
+    pub fn new() -> Self {
+        Self {
+            specs: vec![
+                LazySpec::new("llava", || Box::new(LlavaSpec)),
+                LazySpec::new("qwen_vl", || Box::new(QwenVLVisionSpec)),
+                LazySpec::new("phi3_v", || Box::new(Phi3VisionSpec)),
+            ],
+        }
+    }
+
+    pub fn lookup<'a>(&'a self, metadata: &ModelMetadata) -> Option<&'a dyn ModelProcessorSpec> {
+        for spec in &self.specs {
+            let spec_ref = spec.get();
+            if spec_ref.matches(metadata) {
+                return Some(spec_ref);
+            }
+        }
+        None
+    }
+}
+
+impl Default for ModelRegistry {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+struct LazySpec {
+    inner: Lazy<Box<dyn ModelProcessorSpec>>,
+}
+
+impl LazySpec {
+    fn new(_id: &'static str, factory: fn() -> Box<dyn ModelProcessorSpec>) -> Self {
+        Self {
+            inner: Lazy::new(factory),
+        }
+    }
+
+    fn get(&self) -> &dyn ModelProcessorSpec {
+        self.inner.as_ref()
+    }
+}
+
+struct LlavaSpec;
+
+impl LlavaSpec {
+    fn patch_size(metadata: &ModelMetadata) -> u32 {
+        metadata
+            .config_u32(&["vision_config", "patch_size"])
+            .unwrap_or(14)
+    }
+
+    fn tokens_per_image(metadata: &ModelMetadata, size: &ImageSize) -> usize {
+        let patch = Self::patch_size(metadata);
+        let cols = size.width.div_ceil(patch) as usize;
+        let rows = size.height.div_ceil(patch) as usize;
+        cols * rows
+    }
+}
+
+impl ModelProcessorSpec for LlavaSpec {
+    fn name(&self) -> &'static str {
+        "llava"
+    }
+
+    fn matches(&self, metadata: &ModelMetadata) -> bool {
+        metadata.model_id.to_ascii_lowercase().contains("llava")
+    }
+
+    fn placeholder_token(&self, _metadata: &ModelMetadata) -> RegistryResult<String> {
+        Ok("<image>".to_string())
+    }
+
+    fn placeholder_token_id(&self, metadata: &ModelMetadata) -> RegistryResult<TokenId> {
+        if let Some(value) = metadata.config_u32(&["image_token_index"]) {
+            return Ok(value as TokenId);
+        }
+        metadata.token_id("<image>")
+    }
+
+    fn modality_limits(
+        &self,
+        _metadata: &ModelMetadata,
+    ) -> RegistryResult<HashMap<Modality, usize>> {
+        Ok(HashMap::from([(Modality::Image, 4)]))
+    }
+
+    fn processor_kwargs(&self, _metadata: &ModelMetadata) -> RegistryResult<Value> {
+        Ok(json!({}))
+    }
+
+    fn prompt_replacements(
+        &self,
+        metadata: &ModelMetadata,
+        image_sizes: &[ImageSize],
+    ) -> RegistryResult<Vec<PromptReplacement>> {
+        let token_id = self.placeholder_token_id(metadata)?;
+        let token = self.placeholder_token(metadata)?;
+        Ok(image_sizes
+            .iter()
+            .map(|size| {
+                let count = Self::tokens_per_image(metadata, size);
+                PromptReplacement::repeated(Modality::Image, &token, token_id, count)
+            })
+            .collect())
+    }
+}
+
+struct QwenVLVisionSpec;
+
+impl QwenVLVisionSpec {
+    fn pad_token_id(metadata: &ModelMetadata) -> RegistryResult<TokenId> {
+        metadata
+            .config_u32(&["vision_token_id"])
+            .map(|v| v as TokenId)
+            .ok_or_else(|| ModelRegistryError::MissingConfigField {
+                field: "vision_token_id".to_string(),
+            })
+    }
+
+    fn start_token_id(metadata: &ModelMetadata) -> RegistryResult<TokenId> {
+        metadata
+            .config_u32(&["vision_start_token_id"])
+            .map(|v| v as TokenId)
+            .ok_or_else(|| ModelRegistryError::MissingConfigField {
+                field: "vision_start_token_id".to_string(),
+            })
+    }
+
+    fn patch_grid(metadata: &ModelMetadata, size: &ImageSize) -> (usize, usize) {
+        let patch = metadata
+            .config_u32(&["vision_config", "patch_size"])
+            .unwrap_or(14);
+        let cols = size.width.div_ceil(patch) as usize;
+        let rows = size.height.div_ceil(patch) as usize;
+        (rows, cols)
+    }
+}
+
+impl ModelProcessorSpec for QwenVLVisionSpec {
+    fn name(&self) -> &'static str {
+        "qwen_vl"
+    }
+
+    fn matches(&self, metadata: &ModelMetadata) -> bool {
+        metadata.model_id.to_ascii_lowercase().contains("qwen")
+            && metadata.model_id.to_ascii_lowercase().contains("vl")
+    }
+
+    fn placeholder_token(&self, _metadata: &ModelMetadata) -> RegistryResult<String> {
+        Ok("<image>".to_string())
+    }
+
+    fn placeholder_token_id(&self, metadata: &ModelMetadata) -> RegistryResult<TokenId> {
+        metadata
+            .config_u32(&["image_token_id"])
+            .map(|v| v as TokenId)
+            .ok_or_else(|| ModelRegistryError::MissingConfigField {
+                field: "image_token_id".to_string(),
+            })
+    }
+
+    fn modality_limits(
+        &self,
+        _metadata: &ModelMetadata,
+    ) -> RegistryResult<HashMap<Modality, usize>> {
+        Ok(HashMap::from([(Modality::Image, 10)]))
+    }
+
+    fn processor_kwargs(&self, _metadata: &ModelMetadata) -> RegistryResult<Value> {
+        Ok(json!({}))
+    }
+
+    fn prompt_replacements(
+        &self,
+        metadata: &ModelMetadata,
+        image_sizes: &[ImageSize],
+    ) -> RegistryResult<Vec<PromptReplacement>> {
+        let start_token_id = Self::start_token_id(metadata)?;
+        let pad_token_id = Self::pad_token_id(metadata)?;
+        let placeholder_token = self.placeholder_token(metadata)?;
+        Ok(image_sizes
+            .iter()
+            .map(|size| {
+                let (rows, cols) = Self::patch_grid(metadata, size);
+                let pad_len = rows * cols;
+                let mut tokens = Vec::with_capacity(pad_len + 1);
+                tokens.push(start_token_id);
+                tokens.extend(std::iter::repeat_n(pad_token_id, pad_len));
+                PromptReplacement::sequence(Modality::Image, &placeholder_token, tokens)
+            })
+            .collect())
+    }
+}
+
+struct Phi3VisionSpec;
+
+impl Phi3VisionSpec {
+    fn tokens_per_image(metadata: &ModelMetadata) -> usize {
+        metadata
+            .config_u32(&["img_processor", "num_img_tokens"])
+            .unwrap_or(256) as usize
+    }
+}
+
+impl ModelProcessorSpec for Phi3VisionSpec {
+    fn name(&self) -> &'static str {
+        "phi3_v"
+    }
+
+    fn matches(&self, metadata: &ModelMetadata) -> bool {
+        let id = metadata.model_id.to_ascii_lowercase();
+        id.contains("phi") && id.contains("vision")
+    }
+
+    fn placeholder_token(&self, _metadata: &ModelMetadata) -> RegistryResult<String> {
+        Ok("<image>".to_owned())
+    }
+
+    fn placeholder_token_id(&self, metadata: &ModelMetadata) -> RegistryResult<TokenId> {
+        metadata.token_id("<image>")
+    }
+
+    fn modality_limits(
+        &self,
+        _metadata: &ModelMetadata,
+    ) -> RegistryResult<HashMap<Modality, usize>> {
+        Ok(HashMap::from([(Modality::Image, 4)]))
+    }
+
+    fn processor_kwargs(&self, _metadata: &ModelMetadata) -> RegistryResult<Value> {
+        Ok(json!({}))
+    }
+
+    fn prompt_replacements(
+        &self,
+        metadata: &ModelMetadata,
+        image_sizes: &[ImageSize],
+    ) -> RegistryResult<Vec<PromptReplacement>> {
+        let token_id = self.placeholder_token_id(metadata)?;
+        let token = self.placeholder_token(metadata)?;
+        let count = Self::tokens_per_image(metadata);
+        Ok(image_sizes
+            .iter()
+            .map(|_| PromptReplacement::repeated(Modality::Image, &token, token_id, count))
+            .collect())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+
+    use serde_json::json;
+
+    use super::*;
+    use crate::tokenizer::traits::{
+        Decoder, Encoder, Encoding, SpecialTokens, Tokenizer as TokenizerTrait,
+    };
+
+    struct TestTokenizer {
+        vocab: HashMap<String, u32>,
+    }
+
+    impl TestTokenizer {
+        fn new(pairs: &[(&str, u32)]) -> Self {
+            let vocab = pairs
+                .iter()
+                .map(|(token, id)| ((*token).to_string(), *id))
+                .collect();
+            Self { vocab }
+        }
+    }
+
+    impl Encoder for TestTokenizer {
+        fn encode(&self, _input: &str) -> anyhow::Result<Encoding> {
+            Ok(Encoding::Sp(Vec::new()))
+        }
+
+        fn encode_batch(&self, inputs: &[&str]) -> anyhow::Result<Vec<Encoding>> {
+            inputs.iter().map(|_| self.encode("")).collect()
+        }
+    }
+
+    impl Decoder for TestTokenizer {
+        fn decode(&self, _token_ids: &[u32], _skip_special_tokens: bool) -> anyhow::Result<String> {
+            Ok(String::new())
+        }
+    }
+
+    impl TokenizerTrait for TestTokenizer {
+        fn vocab_size(&self) -> usize {
+            self.vocab.len()
+        }
+
+        fn get_special_tokens(&self) -> &SpecialTokens {
+            static TOKENS: Lazy<SpecialTokens> = Lazy::new(|| SpecialTokens {
+                bos_token: None,
+                eos_token: None,
+                unk_token: None,
+                sep_token: None,
+                pad_token: None,
+                cls_token: None,
+                mask_token: None,
+                additional_special_tokens: vec![],
+            });
+            &TOKENS
+        }
+
+        fn token_to_id(&self, token: &str) -> Option<u32> {
+            self.vocab.get(token).copied()
+        }
+
+        fn id_to_token(&self, _id: u32) -> Option<String> {
+            None
+        }
+
+        fn as_any(&self) -> &dyn std::any::Any {
+            self
+        }
+    }
+
+    #[test]
+    fn llava_prompt_replacement_uses_config_ids() {
+        let tokenizer = TestTokenizer::new(&[("<image>", 32000)]);
+        let config = json!({
+            "model_type": "llava",
+            "image_token_index": 32000,
+            "vision_config": {"patch_size": 14}
+        });
+        let metadata = ModelMetadata {
+            model_id: "llava-v1.5",
+            tokenizer: &tokenizer,
+            config: &config,
+        };
+        let registry = ModelRegistry::new();
+        let spec = registry.lookup(&metadata).expect("llava spec");
+        let replacements = spec
+            .prompt_replacements(&metadata, &[ImageSize::new(336, 336)])
+            .unwrap();
+        assert_eq!(replacements[0].tokens.len(), 576);
+    }
+
+    #[test]
+    fn qwen_vision_uses_config_token_ids() {
+        let tokenizer = TestTokenizer::new(&[("<image>", 999)]);
+        let config = json!({
+            "model_type": "qwen2_vl",
+            "vision_start_token_id": 151652,
+            "vision_token_id": 151654,
+            "image_token_id": 151655,
+            "vision_config": {"patch_size": 14}
+        });
+        let metadata = ModelMetadata {
+            model_id: "Qwen2-VL-7B",
+            tokenizer: &tokenizer,
+            config: &config,
+        };
+        let registry = ModelRegistry::new();
+        let spec = registry.lookup(&metadata).expect("qwen spec");
+        let replacements = spec
+            .prompt_replacements(&metadata, &[ImageSize::new(448, 448)])
+            .unwrap();
+        // 448/14 = 32 patches => 1024 pad tokens + 1 start token
+        assert_eq!(replacements[0].tokens.len(), 1025);
+        assert_eq!(replacements[0].tokens[0], 151652);
+        assert_eq!(replacements[0].tokens[1], 151654);
+    }
+
+    #[test]
+    fn phi3_uses_num_img_tokens() {
+        let tokenizer = TestTokenizer::new(&[("<image>", 555)]);
+        let config = json!({
+            "model_type": "phi3_v",
+            "img_processor": {"num_img_tokens": 144}
+        });
+        let metadata = ModelMetadata {
+            model_id: "Phi-3-vision",
+            tokenizer: &tokenizer,
+            config: &config,
+        };
+        let registry = ModelRegistry::new();
+        let spec = registry.lookup(&metadata).expect("phi3 spec");
+        let replacements = spec
+            .prompt_replacements(&metadata, &[ImageSize::new(336, 336)])
+            .unwrap();
+        assert_eq!(replacements[0].tokens.len(), 144);
+        assert_eq!(replacements[0].tokens[0], 555);
+    }
+}
diff --git a/sgl-router/src/multimodal/tracker.rs b/sgl-router/src/multimodal/tracker.rs
new file mode 100644
index 000000000..25a5bc668
--- /dev/null
+++ b/sgl-router/src/multimodal/tracker.rs
@@ -0,0 +1,176 @@
+use std::{collections::HashMap, sync::Arc};
+
+use tokio::task::JoinHandle;
+
+use super::{
+    error::{MultiModalError, MultiModalResult},
+    media::{ImageFetchConfig, MediaConnector, MediaSource},
+    types::{
+        ChatContentPart, ConversationSegment, ImageDetail, Modality, MultiModalData,
+        MultiModalUUIDs, PlaceholderHandle, PlaceholderMap, TrackedMedia, DEFAULT_PLACEHOLDERS,
+    },
+};
+
+type PendingTask = JoinHandle<MultiModalResult<TrackedMedia>>;
+
+#[derive(Debug, Clone)]
+pub struct TrackerConfig {
+    pub placeholder_tokens: HashMap<Modality, String>,
+    pub modality_limits: HashMap<Modality, usize>,
+}
+
+impl Default for TrackerConfig {
+    fn default() -> Self {
+        Self {
+            placeholder_tokens: DEFAULT_PLACEHOLDERS
+                .iter()
+                .map(|(k, v)| (*k, (*v).to_string()))
+                .collect(),
+            modality_limits: HashMap::new(),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct TrackerOutput {
+    pub conversation: Vec<ConversationSegment>,
+    pub data: MultiModalData,
+    pub uuids: MultiModalUUIDs,
+    pub placeholders: PlaceholderMap,
+}
+
+pub struct AsyncMultiModalTracker {
+    media_connector: Arc<MediaConnector>,
+    config: TrackerConfig,
+    pending: HashMap<Modality, Vec<PendingTask>>,
+    placeholders: PlaceholderMap,
+    conversation: Vec<ConversationSegment>,
+    uuids: MultiModalUUIDs,
+    counts: HashMap<Modality, usize>,
+}
+
+impl AsyncMultiModalTracker {
+    pub fn new(media_connector: Arc<MediaConnector>, config: TrackerConfig) -> Self {
+        Self {
+            media_connector,
+            config,
+            pending: HashMap::new(),
+            placeholders: PlaceholderMap::new(),
+            conversation: Vec::new(),
+            uuids: HashMap::new(),
+            counts: HashMap::new(),
+        }
+    }
+
+    pub fn push_part(&mut self, part: ChatContentPart) -> MultiModalResult<()> {
+        match part {
+            ChatContentPart::Text { text } => {
+                if !text.is_empty() {
+                    self.conversation.push(ConversationSegment::text(text));
+                }
+                Ok(())
+            }
+            ChatContentPart::ImageUrl { url, detail, uuid } => {
+                self.enqueue_image(MediaSource::Url(url), detail.unwrap_or_default(), uuid)
+            }
+            ChatContentPart::ImageData {
+                data,
+                mime_type: _,
+                uuid,
+                detail,
+            } => self.enqueue_image(
+                MediaSource::InlineBytes(data),
+                detail.unwrap_or_default(),
+                uuid,
+            ),
+            ChatContentPart::ImageEmbeds { .. } => {
+                Err(MultiModalError::UnsupportedContent("image_embeds"))
+            }
+        }
+    }
+
+    pub async fn finalize(mut self) -> MultiModalResult<TrackerOutput> {
+        let mut data = MultiModalData::new();
+        for (modality, tasks) in self.pending.drain() {
+            let mut items = Vec::with_capacity(tasks.len());
+            for task in tasks {
+                let media = task.await??;
+                items.push(media);
+            }
+            data.insert(modality, items);
+        }
+
+        Ok(TrackerOutput {
+            conversation: self.conversation,
+            data,
+            uuids: self.uuids,
+            placeholders: self.placeholders,
+        })
+    }
+
+    fn placeholder_token(&self, modality: Modality) -> &str {
+        if let Some(token) = self.config.placeholder_tokens.get(&modality) {
+            token.as_str()
+        } else {
+            DEFAULT_PLACEHOLDERS
+                .get(&modality)
+                .copied()
+                .unwrap_or("<mm>")
+        }
+    }
+
+    fn next_index(&mut self, modality: Modality) -> MultiModalResult<usize> {
+        let count = self.counts.entry(modality).or_insert(0);
+        let next = *count;
+        let limit = self.config.modality_limits.get(&modality).copied();
+        if let Some(limit) = limit {
+            if next >= limit {
+                return Err(MultiModalError::ModalityLimit { modality, limit });
+            }
+        }
+        *count += 1;
+        Ok(next)
+    }
+
+    fn record_uuid(&mut self, modality: Modality, uuid: Option<String>) {
+        self.uuids.entry(modality).or_default().push(uuid);
+    }
+
+    fn add_placeholder(&mut self, token: String, handle: PlaceholderHandle) {
+        self.placeholders.entry(token).or_default().push(handle);
+    }
+
+    fn enqueue_image(
+        &mut self,
+        source: MediaSource,
+        detail: ImageDetail,
+        uuid: Option<String>,
+    ) -> MultiModalResult<()> {
+        let modality = Modality::Image;
+        let idx = self.next_index(modality)?;
+        let token = self.placeholder_token(modality).to_string();
+        let text_position = self.conversation.len();
+        self.conversation
+            .push(ConversationSegment::placeholder(token.clone()));
+        self.add_placeholder(
+            token.clone(),
+            PlaceholderHandle {
+                modality,
+                item_index: idx,
+                text_position,
+            },
+        );
+        self.record_uuid(modality, uuid);
+
+        let connector = Arc::clone(&self.media_connector);
+        let handle = tokio::spawn(async move {
+            let frame = connector
+                .fetch_image(source, ImageFetchConfig { detail })
+                .await?;
+            Ok(TrackedMedia::Image(frame))
+        });
+
+        self.pending.entry(modality).or_default().push(handle);
+        Ok(())
+    }
+}
diff --git a/sgl-router/src/multimodal/types.rs b/sgl-router/src/multimodal/types.rs
new file mode 100644
index 000000000..fe3bb1dc9
--- /dev/null
+++ b/sgl-router/src/multimodal/types.rs
@@ -0,0 +1,290 @@
+use std::{
+    collections::{BTreeMap, HashMap},
+    fmt,
+    path::PathBuf,
+    sync::{Arc, LazyLock},
+};
+
+use image::DynamicImage;
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+
+/// Supported multimodal modalities.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum Modality {
+    Image,
+    ImageEmbeds,
+    Audio,
+    Video,
+}
+
+impl fmt::Display for Modality {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Modality::Image => write!(f, "image"),
+            Modality::ImageEmbeds => write!(f, "image_embeds"),
+            Modality::Audio => write!(f, "audio"),
+            Modality::Video => write!(f, "video"),
+        }
+    }
+}
+
+/// Simple helper used for default placeholder tokens per modality.
+pub static DEFAULT_PLACEHOLDERS: LazyLock<HashMap<Modality, &'static str>> = LazyLock::new(|| {
+    HashMap::from([
+        (Modality::Image, "<image>"),
+        (Modality::ImageEmbeds, "<image_embeds>"),
+        (Modality::Audio, "<audio>"),
+        (Modality::Video, "<video>"),
+    ])
+});
+
+/// Detail level passed by OpenAI style APIs.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum ImageDetail {
+    #[default]
+    Auto,
+    Low,
+    High,
+}
+
+/// A normalized content part understood by the tracker.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum ChatContentPart {
+    Text {
+        text: String,
+    },
+    ImageUrl {
+        url: String,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        detail: Option<ImageDetail>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        uuid: Option<String>,
+    },
+    ImageData {
+        data: Vec<u8>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        mime_type: Option<String>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        uuid: Option<String>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        detail: Option<ImageDetail>,
+    },
+    ImageEmbeds {
+        payload: Value,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        uuid: Option<String>,
+    },
+}
+
+/// Represents one segment in the conversation after placeholders are inserted.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum ConversationSegment {
+    Text(String),
+    Placeholder { token: String },
+}
+
+impl ConversationSegment {
+    pub fn text<S: Into<String>>(text: S) -> Self {
+        ConversationSegment::Text(text.into())
+    }
+
+    pub fn placeholder<S: Into<String>>(token: S) -> Self {
+        ConversationSegment::Placeholder {
+            token: token.into(),
+        }
+    }
+}
+
+/// Metadata describing where placeholder tokens were inserted.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PlaceholderHandle {
+    pub modality: Modality,
+    pub item_index: usize,
+    pub text_position: usize,
+}
+
+pub type PlaceholderMap = HashMap<String, Vec<PlaceholderHandle>>;
+
+/// Image source metadata (useful for hashing & tracing).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum ImageSource {
+    Url { url: String },
+    DataUrl,
+    InlineBytes,
+    File { path: PathBuf },
+}
+
+/// Concrete image payload captured by the media connector.
+#[derive(Debug)]
+pub struct ImageFrame {
+    image: DynamicImage,
+    raw_bytes: Arc<Vec<u8>>,
+    pub detail: ImageDetail,
+    pub source: ImageSource,
+}
+
+impl ImageFrame {
+    pub fn new(
+        image: DynamicImage,
+        raw_bytes: Arc<Vec<u8>>,
+        detail: ImageDetail,
+        source: ImageSource,
+    ) -> Self {
+        Self {
+            image,
+            raw_bytes,
+            detail,
+            source,
+        }
+    }
+
+    pub fn data(&self) -> &DynamicImage {
+        &self.image
+    }
+
+    pub fn raw_bytes(&self) -> &[u8] {
+        self.raw_bytes.as_slice()
+    }
+
+    pub fn source(&self) -> &ImageSource {
+        &self.source
+    }
+
+    pub fn size(&self) -> ImageSize {
+        ImageSize::new(self.image.width(), self.image.height())
+    }
+}
+
+/// Container for all supported multimodal media objects.
+#[derive(Debug, Clone)]
+pub enum TrackedMedia {
+    Image(Arc<ImageFrame>),
+    /// Placeholder variants for future modalities.
+    Audio,
+    Video,
+    Embeddings,
+}
+
+pub type MultiModalData = HashMap<Modality, Vec<TrackedMedia>>;
+pub type MultiModalUUIDs = HashMap<Modality, Vec<Option<String>>>;
+
+pub type TokenId = i32;
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
+pub struct ImageSize {
+    pub width: u32,
+    pub height: u32,
+}
+
+impl ImageSize {
+    pub fn new(width: u32, height: u32) -> Self {
+        Self { width, height }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct PlaceholderRange {
+    pub offset: usize,
+    pub length: usize,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct MultiModalTensor {
+    pub shape: Vec<usize>,
+    pub dtype: String,
+    #[serde(with = "serde_bytes")]
+    pub data: Vec<u8>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum MultiModalValue {
+    Tensor(MultiModalTensor),
+    Json(Value),
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct MultiModalInputs {
+    pub prompt_token_ids: Vec<u32>,
+    #[serde(default)]
+    pub mm_kwargs: BTreeMap<String, Vec<MultiModalValue>>,
+    #[serde(default)]
+    pub mm_hashes: BTreeMap<String, Vec<String>>,
+    #[serde(default)]
+    pub mm_placeholders: BTreeMap<String, Vec<PlaceholderRange>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cache_salt: Option<String>,
+}
+
+impl MultiModalInputs {
+    pub fn new(prompt_token_ids: Vec<u32>) -> Self {
+        Self {
+            prompt_token_ids,
+            ..Default::default()
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct PromptReplacement {
+    pub modality: Modality,
+    pub placeholder_token: String,
+    pub tokens: Vec<TokenId>,
+}
+
+impl PromptReplacement {
+    pub fn repeated(
+        modality: Modality,
+        placeholder_token: &str,
+        token_id: TokenId,
+        count: usize,
+    ) -> Self {
+        Self {
+            modality,
+            placeholder_token: placeholder_token.to_string(),
+            tokens: vec![token_id; count],
+        }
+    }
+
+    pub fn sequence(modality: Modality, placeholder_token: &str, sequence: Vec<TokenId>) -> Self {
+        Self {
+            modality,
+            placeholder_token: placeholder_token.to_string(),
+            tokens: sequence,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn multimodal_inputs_defaults() {
+        let inputs = MultiModalInputs::new(vec![1, 2, 3]);
+        assert_eq!(inputs.prompt_token_ids, vec![1, 2, 3]);
+        assert!(inputs.mm_kwargs.is_empty());
+    }
+
+    #[test]
+    fn placeholder_range_serializes() {
+        let range = PlaceholderRange {
+            offset: 10,
+            length: 4,
+        };
+        let json = serde_json::to_string(&range).unwrap();
+        assert!(json.contains("offset"));
+    }
+
+    #[test]
+    fn prompt_replacement_builders() {
+        let rep = PromptReplacement::repeated(Modality::Image, "<image>", 100, 3);
+        assert_eq!(rep.tokens, vec![100, 100, 100]);
+    }
+}
diff --git a/sgl-router/tests/multimodal_tracker_test.rs b/sgl-router/tests/multimodal_tracker_test.rs
new file mode 100644
index 000000000..b1c158b2b
--- /dev/null
+++ b/sgl-router/tests/multimodal_tracker_test.rs
@@ -0,0 +1,151 @@
+use std::{collections::HashMap, path::PathBuf, sync::Arc, time::Duration};
+
+use base64::{engine::general_purpose::STANDARD as BASE64_STANDARD, Engine};
+use reqwest::Client;
+use sgl_model_gateway::multimodal::{
+    AsyncMultiModalTracker, ChatContentPart, ConversationSegment, ImageFetchConfig, ImageSource,
+    MediaConnector, MediaConnectorConfig, MediaSource, Modality, TrackerConfig,
+};
+use tempfile::tempdir;
+
+const TINY_PNG_BASE64: &str =
+    "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNgYAAAAAMAASsJTYQAAAAASUVORK5CYII=";
+
+fn tiny_png_bytes() -> Vec<u8> {
+    BASE64_STANDARD
+        .decode(TINY_PNG_BASE64)
+        .expect("decode tiny png fixture")
+}
+
+fn test_connector(allowed_path: Option<PathBuf>) -> MediaConnector {
+    let client = Client::builder()
+        .timeout(Duration::from_secs(5))
+        .no_proxy()
+        .build()
+        .expect("client");
+    MediaConnector::new(
+        client,
+        MediaConnectorConfig {
+            allowed_domains: None,
+            allowed_local_media_path: allowed_path,
+            fetch_timeout: Duration::from_secs(5),
+        },
+    )
+    .expect("media connector")
+}
+
+#[tokio::test]
+async fn fetch_image_from_inline_bytes() {
+    let connector = test_connector(None);
+    let bytes = tiny_png_bytes();
+    let frame = connector
+        .fetch_image(
+            MediaSource::InlineBytes(bytes.clone()),
+            ImageFetchConfig::default(),
+        )
+        .await
+        .expect("inline image");
+    assert_eq!(frame.data().width(), 1);
+    assert_eq!(frame.data().height(), 1);
+    assert_eq!(frame.raw_bytes(), bytes.as_slice());
+}
+
+#[tokio::test]
+async fn fetch_image_from_data_url() {
+    let connector = test_connector(None);
+    let bytes = tiny_png_bytes();
+    let data_url = format!(
+        "data:image/png;base64,{}",
+        BASE64_STANDARD.encode(bytes.clone())
+    );
+
+    let frame = connector
+        .fetch_image(MediaSource::DataUrl(data_url), ImageFetchConfig::default())
+        .await
+        .expect("data url");
+    assert_eq!(frame.data().width(), 1);
+    assert_eq!(frame.raw_bytes(), bytes.as_slice());
+}
+
+#[tokio::test]
+async fn fetch_image_from_file() {
+    let tmp = tempdir().expect("tempdir");
+    let allowed_root = std::fs::canonicalize(tmp.path()).expect("canonical tmp path");
+    let file_path = allowed_root.join("tiny.png");
+    std::fs::write(&file_path, tiny_png_bytes()).expect("write png");
+
+    let connector = test_connector(Some(allowed_root));
+    let frame = connector
+        .fetch_image(
+            MediaSource::File(file_path.clone()),
+            ImageFetchConfig::default(),
+        )
+        .await
+        .expect("file png");
+    assert_eq!(frame.data().width(), 1);
+    let expected = std::fs::canonicalize(&file_path).expect("canonical path");
+    match frame.source() {
+        ImageSource::File { path } => assert_eq!(path, &expected),
+        other => panic!("expected file source, got {:?}", other),
+    }
+}
+
+#[tokio::test]
+async fn tracker_collects_conversation_and_placeholders() {
+    let connector = Arc::new(test_connector(None));
+    let mut tracker = AsyncMultiModalTracker::new(
+        connector,
+        TrackerConfig {
+            placeholder_tokens: Default::default(),
+            modality_limits: HashMap::from([(Modality::Image, 2)]),
+        },
+    );
+
+    tracker
+        .push_part(ChatContentPart::Text {
+            text: "before".into(),
+        })
+        .expect("text part");
+    tracker
+        .push_part(ChatContentPart::ImageData {
+            data: tiny_png_bytes(),
+            mime_type: Some("image/png".into()),
+            uuid: Some("img-1".into()),
+            detail: None,
+        })
+        .expect("image part");
+    tracker
+        .push_part(ChatContentPart::Text {
+            text: "after".into(),
+        })
+        .expect("text part");
+
+    let output = tracker.finalize().await.expect("tracker finalize");
+    assert_eq!(output.conversation.len(), 3);
+    assert!(matches!(
+        &output.conversation[0],
+        ConversationSegment::Text(text) if text == "before"
+    ));
+    assert!(matches!(
+        &output.conversation[1],
+        ConversationSegment::Placeholder { token } if token == "<image>"
+    ));
+    assert!(matches!(
+        &output.conversation[2],
+        ConversationSegment::Text(text) if text == "after"
+    ));
+
+    let images = output.data.get(&Modality::Image).expect("image entry");
+    assert_eq!(images.len(), 1);
+
+    let uuids = output.uuids.get(&Modality::Image).expect("uuid entry");
+    assert_eq!(uuids, &vec![Some("img-1".into())]);
+
+    let placeholders = output
+        .placeholders
+        .get("<image>")
+        .expect("placeholder entry");
+    assert_eq!(placeholders.len(), 1);
+    assert_eq!(placeholders[0].text_position, 1);
+    assert_eq!(placeholders[0].item_index, 0);
+}