feat: add sha256 hash metadata storage in finalize

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/meta_plugin/digest.rs

@@ -1,6 +1,7 @@
 use anyhow::Result;
 use sha2::{Digest, Sha256};
 use std::time::Instant;
+use rusqlite::Connection;
 
 use crate::meta_plugin::MetaPlugin;
 
@@ -8,6 +9,8 @@ use crate::meta_plugin::MetaPlugin;
 pub struct DigestSha256MetaPlugin {
     hasher: Sha256,
     meta_name: String,
+    item_id: Option<i64>,
+    conn: Option<*mut Connection>,
 }
 
 impl DigestSha256MetaPlugin {
@@ -15,6 +18,8 @@ impl DigestSha256MetaPlugin {
         DigestSha256MetaPlugin {
             hasher: Sha256::new(),
             meta_name: "digest_sha256".to_string(),
+            item_id: None,
+            conn: None,
         }
     }
 }
@@ -24,7 +29,30 @@ impl MetaPlugin for DigestSha256MetaPlugin {
         true
     }
     
+    fn initialize(&mut self, conn: &Connection, item_id: i64) -> Result<()> {
+        self.item_id = Some(item_id);
+        // Store raw pointer to connection - unsafe but necessary for this design
+        self.conn = Some(conn as *const _ as *mut Connection);
+        Ok(())
+    }
+    
     fn finalize(&mut self) -> Result<()> {
+        if let (Some(conn), Some(item_id)) = (self.conn, self.item_id) {
+            // Convert raw pointer back to reference (unsafe)
+            let conn_ref = unsafe { &*conn };
+            
+            // Finalize the hash
+            let hash_result = self.hasher.finalize_reset();
+            let hex_string = format!("{:x}", hash_result);
+            
+            // Save the hash as metadata
+            let meta = crate::db::Meta {
+                id: item_id,
+                name: self.meta_name.clone(),
+                value: hex_string,
+            };
+            crate::db::store_meta(conn_ref, meta)?;
+        }
         Ok(())
     }