Merge feature/fix-gguf-shard-selection into develop

Fix backend de sélection GGUF (fichier fusionné prioritaire sur les
shards partiels) — QA vert : cargo test -p infrastructure/application,
cargo check --workspace, 3 nouveaux tests unitaires.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/infrastructure/src/model_server/mod.rs

@@ -89,6 +89,11 @@ impl HfModelArtifactDownloader {
     }
 
     /// Deterministic cache path for a Hugging Face model reference.
+    ///
+    /// This is the local path used for a single **merged** (non-sharded) GGUF file, renamed to a
+    /// synthetic `{quant}.gguf` name. Sharded files are never renamed this way: llama.cpp
+    /// discovers multi-part siblings by pattern-matching the *original* HF filename in the same
+    /// directory, so shard files keep their remote name (see `local_path_for_filename`).
     #[must_use]
     pub fn cache_path_for(&self, repo: &HfModelRef) -> PathBuf {
         let (base, quant) = split_hf_ref(repo);
@@ -98,7 +103,56 @@ impl HfModelArtifactDownloader {
             .join(format!("{}.gguf", safe_cache_component(file_stem)))
     }
 
-    async fn resolve_remote_filename(&self, repo: &HfModelRef) -> Result<String, ModelServerError> {
+    fn cache_dir_for(&self, repo: &HfModelRef) -> PathBuf {
+        let (base, _) = split_hf_ref(repo);
+        self.cache_dir.join(base.replace('/', "--"))
+    }
+
+    /// Local path for a remote filename that is part of a multi-shard set: the original name is
+    /// preserved (sanitized) so llama.cpp's shard autoload can find siblings by pattern.
+    fn local_path_for_shard(&self, repo: &HfModelRef, remote_filename: &str) -> PathBuf {
+        self.cache_dir_for(repo)
+            .join(safe_cache_component(remote_filename))
+    }
+
+    fn manifest_path_for(&self, repo: &HfModelRef) -> PathBuf {
+        let (_, quant) = split_hf_ref(repo);
+        let file_stem = quant.unwrap_or("model");
+        self.cache_dir_for(repo)
+            .join(format!("{}.manifest.json", safe_cache_component(file_stem)))
+    }
+
+    /// Reads a manifest of a previously-downloaded shard set, if present and complete on disk.
+    fn cached_shard_set(&self, repo: &HfModelRef) -> Option<Vec<PathBuf>> {
+        let manifest_path = self.manifest_path_for(repo);
+        let raw = std::fs::read(&manifest_path).ok()?;
+        let manifest: ShardManifest = serde_json::from_slice(&raw).ok()?;
+        let dir = self.cache_dir_for(repo);
+        let paths: Vec<PathBuf> = manifest
+            .files
+            .iter()
+            .map(|filename| dir.join(filename))
+            .collect();
+        if paths.iter().all(|path| path.is_file()) {
+            Some(paths)
+        } else {
+            None
+        }
+    }
+
+    fn write_shard_manifest(&self, repo: &HfModelRef, filenames: &[String]) -> std::io::Result<()> {
+        let manifest_path = self.manifest_path_for(repo);
+        let manifest = ShardManifest {
+            files: filenames.to_vec(),
+        };
+        let json = serde_json::to_vec(&manifest)?;
+        std::fs::write(manifest_path, json)
+    }
+
+    async fn resolve_remote_filenames(
+        &self,
+        repo: &HfModelRef,
+    ) -> Result<Vec<String>, ModelServerError> {
         let (base, quant) = split_hf_ref(repo);
         let url = format!("https://huggingface.co/api/models/{base}");
         let response = self
@@ -117,15 +171,22 @@ impl HfModelArtifactDownloader {
             .json()
             .await
             .map_err(|e| ModelServerError::Probe(e.to_string()))?;
-        select_gguf_file(&metadata.siblings, quant).ok_or_else(|| {
-            ModelServerError::PathNotAccessible(format!(
+        let files = select_gguf_files(&metadata.siblings, quant);
+        if files.is_empty() {
+            return Err(ModelServerError::PathNotAccessible(format!(
                 "no matching .gguf artifact found for {}",
                 repo.as_str()
-            ))
-        })
+            )));
+        }
+        Ok(files)
     }
 }
 
+#[derive(Debug, Default, Serialize, Deserialize)]
+struct ShardManifest {
+    files: Vec<String>,
+}
+
 #[async_trait]
 impl ModelArtifactDownloader for HfModelArtifactDownloader {
     async fn resolve_hf_model(
@@ -137,72 +198,105 @@ impl ModelArtifactDownloader for HfModelArtifactDownloader {
         if cancel.is_cancelled() {
             return Err(ModelServerError::Cancelled);
         }
-        let path = self.cache_path_for(repo);
-        if path.is_file() {
+
+        // Fast path 1: a single merged file was already downloaded (synthetic name), no network needed.
+        let merged_path = self.cache_path_for(repo);
+        if merged_path.is_file() {
             return Ok(ModelArtifactResolution {
-                path: model_path_from_pathbuf(path)?,
+                path: model_path_from_pathbuf(merged_path)?,
                 cache_hit: true,
             });
         }
+        // Fast path 2: a previously-downloaded shard set is fully present on disk, no network needed.
+        if let Some(paths) = self.cached_shard_set(repo) {
+            if let Some(first) = paths.into_iter().next() {
+                return Ok(ModelArtifactResolution {
+                    path: model_path_from_pathbuf(first)?,
+                    cache_hit: true,
+                });
+            }
+        }
 
-        let filename = self.resolve_remote_filename(repo).await?;
+        let filenames = self.resolve_remote_filenames(repo).await?;
         if cancel.is_cancelled() {
             return Err(ModelServerError::Cancelled);
         }
+        let is_shard_set = filenames.len() > 1;
+        let targets: Vec<PathBuf> = if is_shard_set {
+            filenames
+                .iter()
+                .map(|filename| self.local_path_for_shard(repo, filename))
+                .collect()
+        } else {
+            vec![merged_path.clone()]
+        };
+
         let (base, _) = split_hf_ref(repo);
-        let url = format!(
-            "https://huggingface.co/{base}/resolve/main/{}",
-            url_path_segment(&filename)
-        );
-        let response = self
-            .client
-            .get(url)
-            .send()
-            .await
-            .map_err(|e| ModelServerError::Probe(e.to_string()))?;
-        if !response.status().is_success() {
-            return Err(ModelServerError::Probe(format!(
-                "huggingface artifact download returned {}",
-                response.status()
-            )));
-        }
-        if let Some(parent) = path.parent() {
-            tokio::fs::create_dir_all(parent)
-                .await
-                .map_err(|e| ModelServerError::Store(e.to_string()))?;
-        }
-        let tmp_path = path.with_extension("gguf.part");
-        let mut file = tokio::fs::File::create(&tmp_path)
-            .await
-            .map_err(|e| ModelServerError::Store(e.to_string()))?;
-        let total = response.content_length();
-        let mut downloaded = 0_u64;
-        let mut stream = response.bytes_stream();
-        while let Some(chunk) = stream.next().await {
+        let total_files = filenames.len() as u64;
+        for (index, (filename, target)) in filenames.iter().zip(targets.iter()).enumerate() {
             if cancel.is_cancelled() {
-                let _ = tokio::fs::remove_file(&tmp_path).await;
                 return Err(ModelServerError::Cancelled);
             }
-            let chunk = chunk.map_err(|e| ModelServerError::Probe(e.to_string()))?;
-            file.write_all(&chunk)
+            let url = format!(
+                "https://huggingface.co/{base}/resolve/main/{}",
+                url_path_segment(filename)
+            );
+            let response = self
+                .client
+                .get(url)
+                .send()
+                .await
+                .map_err(|e| ModelServerError::Probe(e.to_string()))?;
+            if !response.status().is_success() {
+                return Err(ModelServerError::Probe(format!(
+                    "huggingface artifact download returned {}",
+                    response.status()
+                )));
+            }
+            if let Some(parent) = target.parent() {
+                tokio::fs::create_dir_all(parent)
+                    .await
+                    .map_err(|e| ModelServerError::Store(e.to_string()))?;
+            }
+            let tmp_path = PathBuf::from(format!("{}.part", target.to_string_lossy()));
+            let mut file = tokio::fs::File::create(&tmp_path)
+                .await
+                .map_err(|e| ModelServerError::Store(e.to_string()))?;
+            let total = response.content_length();
+            let mut downloaded = 0_u64;
+            let mut stream = response.bytes_stream();
+            while let Some(chunk) = stream.next().await {
+                if cancel.is_cancelled() {
+                    let _ = tokio::fs::remove_file(&tmp_path).await;
+                    return Err(ModelServerError::Cancelled);
+                }
+                let chunk = chunk.map_err(|e| ModelServerError::Probe(e.to_string()))?;
+                file.write_all(&chunk)
+                    .await
+                    .map_err(|e| ModelServerError::Store(e.to_string()))?;
+                downloaded += chunk.len() as u64;
+                progress(ModelArtifactProgress {
+                    downloaded_bytes: Some(downloaded + index as u64 * total.unwrap_or(0)),
+                    total_bytes: total.map(|t| t * total_files),
+                    source: Some(repo.as_str().to_owned()),
+                });
+            }
+            file.flush()
+                .await
+                .map_err(|e| ModelServerError::Store(e.to_string()))?;
+            drop(file);
+            tokio::fs::rename(&tmp_path, target)
                 .await
                 .map_err(|e| ModelServerError::Store(e.to_string()))?;
-            downloaded += chunk.len() as u64;
-            progress(ModelArtifactProgress {
-                downloaded_bytes: Some(downloaded),
-                total_bytes: total,
-                source: Some(repo.as_str().to_owned()),
-            });
         }
-        file.flush()
-            .await
-            .map_err(|e| ModelServerError::Store(e.to_string()))?;
-        drop(file);
-        tokio::fs::rename(&tmp_path, &path)
-            .await
-            .map_err(|e| ModelServerError::Store(e.to_string()))?;
+
+        if is_shard_set {
+            self.write_shard_manifest(repo, &filenames)
+                .map_err(|e| ModelServerError::Store(e.to_string()))?;
+        }
+
         Ok(ModelArtifactResolution {
-            path: model_path_from_pathbuf(path)?,
+            path: model_path_from_pathbuf(targets[0].clone())?,
             cache_hit: false,
         })
     }
@@ -226,21 +320,61 @@ fn split_hf_ref(repo: &HfModelRef) -> (&str, Option<&str>) {
         .map_or((repo.as_str(), None), |(base, quant)| (base, Some(quant)))
 }
 
-fn select_gguf_file(siblings: &[HfSibling], quant: Option<&str>) -> Option<String> {
-    let mut ggufs: Vec<&str> = siblings
+/// Matches the llama.cpp / HF multi-part GGUF naming convention, e.g.
+/// `model-q5_k_m-00001-of-00002.gguf`. Captures the shard index and total shard count.
+fn shard_suffix() -> &'static regex::Regex {
+    static RE: std::sync::OnceLock<regex::Regex> = std::sync::OnceLock::new();
+    RE.get_or_init(|| regex::Regex::new(r"-(\d{5})-of-(\d{5})\.gguf$").expect("valid regex"))
+}
+
+fn shard_index(filename: &str) -> Option<u32> {
+    shard_suffix()
+        .captures(filename)
+        .and_then(|caps| caps.get(1))
+        .and_then(|m| m.as_str().parse().ok())
+}
+
+/// Resolves the ordered set of remote filenames to download for a quantization: the merged
+/// (non-sharded) file if one matches, otherwise all matching shards sorted by index. A merged
+/// file always takes priority over a shard set when both exist in the repo, since it is what
+/// `llama-server --model` expects and a shard set would otherwise be picked first by naive
+/// alphabetical sort ('-' sorts before '.' in ASCII).
+fn select_gguf_files(siblings: &[HfSibling], quant: Option<&str>) -> Vec<String> {
+    let ggufs: Vec<&str> = siblings
         .iter()
         .map(|sibling| sibling.filename.as_str())
         .filter(|filename| filename.ends_with(".gguf"))
         .collect();
-    ggufs.sort_unstable();
-    let Some(quant) = quant else {
-        return ggufs.first().map(|filename| (*filename).to_owned());
+
+    let matching: Vec<&str> = match quant {
+        None => ggufs,
+        Some(quant) => {
+            let quant = quant.to_ascii_lowercase();
+            ggufs
+                .into_iter()
+                .filter(|filename| filename.to_ascii_lowercase().contains(&quant))
+                .collect()
+        }
     };
-    let quant = quant.to_ascii_lowercase();
-    ggufs
-        .into_iter()
-        .find(|filename| filename.to_ascii_lowercase().contains(&quant))
-        .map(str::to_owned)
+
+    let (mut merged, mut shards): (Vec<&str>, Vec<&str>) = (Vec::new(), Vec::new());
+    for filename in matching {
+        if shard_index(filename).is_some() {
+            shards.push(filename);
+        } else {
+            merged.push(filename);
+        }
+    }
+
+    if let Some(first_merged) = {
+        merged.sort_unstable();
+        merged.first()
+    } {
+        return vec![(*first_merged).to_owned()];
+    }
+
+    shards.sort_unstable_by_key(|filename| shard_index(filename).unwrap_or(u32::MAX));
+    shards.into_iter().map(str::to_owned).collect()
 }
 
 fn safe_cache_component(raw: &str) -> String {
@@ -644,3 +778,55 @@ impl ModelServerRegistry for FsModelServerRegistry {
         self.write_doc(&doc).await
     }
 }
+
+#[cfg(test)]
+mod gguf_selection_tests {
+    use super::{select_gguf_files, HfSibling};
+
+    fn sibling(name: &str) -> HfSibling {
+        HfSibling {
+            filename: name.to_owned(),
+        }
+    }
+
+    #[test]
+    fn prefers_merged_file_over_colliding_shards() {
+        let siblings = vec![
+            sibling("qwen2.5-coder-7b-instruct-q5_k_m-00001-of-00002.gguf"),
+            sibling("qwen2.5-coder-7b-instruct-q5_k_m-00002-of-00002.gguf"),
+            sibling("qwen2.5-coder-7b-instruct-q5_k_m.gguf"),
+        ];
+
+        let files = select_gguf_files(&siblings, Some("q5_k_m"));
+
+        assert_eq!(files, vec!["qwen2.5-coder-7b-instruct-q5_k_m.gguf"]);
+    }
+
+    #[test]
+    fn selects_all_shards_sorted_by_index_when_no_merged_file() {
+        let siblings = vec![
+            sibling("model-q4_k_m-00002-of-00003.gguf"),
+            sibling("model-q4_k_m-00001-of-00003.gguf"),
+            sibling("model-q4_k_m-00003-of-00003.gguf"),
+            sibling("model-q8_0-00001-of-00002.gguf"),
+        ];
+
+        let files = select_gguf_files(&siblings, Some("q4_k_m"));
+
+        assert_eq!(
+            files,
+            vec![
+                "model-q4_k_m-00001-of-00003.gguf",
+                "model-q4_k_m-00002-of-00003.gguf",
+                "model-q4_k_m-00003-of-00003.gguf",
+            ]
+        );
+    }
+
+    #[test]
+    fn returns_empty_when_no_match() {
+        let siblings = vec![sibling("model-q4_k_m.gguf")];
+
+        assert!(select_gguf_files(&siblings, Some("q5_k_m")).is_empty());
+    }
+}