Make compaction transitions recoverable

src/engine/gguf.rs

@@ -1,4 +1,5 @@
 use memmap2::{Mmap, MmapOptions};
+use sha2::{Digest, Sha256};
 use std::collections::HashMap;
 use std::fs::File;
 use std::path::{Path, PathBuf};
@@ -176,6 +177,32 @@ impl Gguf {
         self.map.len() as u64
     }
 
+    pub(super) fn checkpoint_identity(&self) -> [u8; 32] {
+        let mut hash = Sha256::new();
+        hash.update(b"DS4Server GGUF checkpoint identity v1");
+        hash.update(
+            self.path
+                .canonicalize()
+                .unwrap_or_else(|_| self.path.clone())
+                .to_string_lossy()
+                .as_bytes(),
+        );
+        hash.update(self.len().to_le_bytes());
+        hash.update(self.data_offset.to_le_bytes());
+        let mut tensors = self.tensors.iter().collect::<Vec<_>>();
+        tensors.sort_by_key(|(name, _)| *name);
+        for (name, tensor) in tensors {
+            hash.update(name.as_bytes());
+            hash.update(tensor.kind.to_le_bytes());
+            hash.update(tensor.offset.to_le_bytes());
+            hash.update(tensor.bytes.to_le_bytes());
+            for dimension in &tensor.dims {
+                hash.update(dimension.to_le_bytes());
+            }
+        }
+        hash.finalize().into()
+    }
+
     pub(super) fn map_ptr(&self) -> *const u8 {
         self.map.as_ptr()
     }