fix(depot): add ltx decode diagnostics

Author: NathanFlurry

engine/packages/depot/src/conveyer/read.rs

@@ -430,8 +430,19 @@ impl Db {
 					.with_context(|| format!("missing source blob for page {pgno}"))?;
 
 				if !decoded_blobs.contains_key(source_key) {
-					let decoded = decode_ltx_v3(blob)
-						.with_context(|| format!("decode source blob for page {pgno}"))?;
+					let decoded = decode_ltx_v3(blob).with_context(|| {
+						let len = blob.len();
+						let head_n = len.min(64);
+						let tail_start = len.saturating_sub(64);
+						format!(
+							"decode source blob for page {pgno}; \
+							 source_key={}; len={}; head={}; tail={}",
+							crate::compaction::shared::hex_lower(source_key),
+							len,
+							crate::compaction::shared::hex_lower(&blob[..head_n]),
+							crate::compaction::shared::hex_lower(&blob[tail_start..]),
+						)
+					})?;
 					decoded_blobs.insert(source_key.clone(), decoded);
 				}
 

engine/packages/depot/src/conveyer/read/cold.rs

@@ -219,8 +219,18 @@ impl Db {
 			let bytes = loaded_objects
 				.get(object_key)
 				.expect("cold object should be loaded before decode");
-			let decoded = decode_ltx_v3(bytes)
-				.with_context(|| format!("decode sqlite cold layer {object_key}"))?;
+			let decoded = decode_ltx_v3(bytes).with_context(|| {
+				let len = bytes.len();
+				let head_n = len.min(64);
+				let tail_start = len.saturating_sub(64);
+				format!(
+					"decode sqlite cold layer {object_key}; \
+					 len={}; head={}; tail={}",
+					len,
+					crate::compaction::shared::hex_lower(&bytes[..head_n]),
+					crate::compaction::shared::hex_lower(&bytes[tail_start..]),
+				)
+			})?;
 			decoded_objects.insert(object_key.to_string(), decoded);
 		}