refactor(db): use rusqlite query_row/optional instead of hand-rolled reads

pending_backlog, earliest_run_after, ChatStore::get and LinkCache::get each
hand-rolled prepare + query + rows.next() for what is a single-row read.
query_row + OptionalExtension::optional is the same statement and the same
error mapping with less scaffolding; the backlog's NULL-on-empty MIN still
goes through the count check, so a pending row with a NULL run_after is not
misread. Also fixes the rustfmt drift from the previous commit.

crates/xmedia-bot/src/link_cache.rs

@@ -9,6 +9,7 @@
 //! by the periodic prune in `main`.
 
 use crate::db::now_f64;
+use rusqlite::OptionalExtension;
 use rusqlite::params;
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
@@ -76,14 +77,16 @@ impl LinkCache {
         let result = self
             .pool
             .with_conn(move |conn| {
-                let mut stmt =
-                    conn.prepare("SELECT payload, created_at FROM link_cache WHERE url = ?1")?;
-                let mut rows = stmt.query(params![key])?;
-                let Some(row) = rows.next()? else {
+                let Some((payload, created_at)) = conn
+                    .query_row(
+                        "SELECT payload, created_at FROM link_cache WHERE url = ?1",
+                        params![key],
+                        |row| Ok((row.get::<_, String>(0)?, row.get::<_, f64>(1)?)),
+                    )
+                    .optional()?
+                else {
                     return Ok(None);
                 };
-                let payload: String = row.get(0)?;
-                let created_at: f64 = row.get(1)?;
                 if now_f64() - created_at > ttl {
                     conn.execute("DELETE FROM link_cache WHERE url = ?1", params![key])?;
                     return Ok(None);

crates/xmedia-bot/src/queue.rs

@@ -294,19 +294,16 @@ impl PersistentTaskQueue {
         let result = self
             .pool
             .with_conn(|conn| {
-                let mut stmt = conn
-                    .prepare("SELECT COUNT(*), MIN(run_after) FROM tasks WHERE status='pending'")?;
-                let mut rows = stmt.query([])?;
-                match rows.next()? {
-                    Some(row) => {
-                        let count = row.get::<_, i64>(0)?;
-                        match row.get::<_, Option<f64>>(1)? {
-                            Some(oldest) if count > 0 => Ok(Some((count, oldest))),
-                            _ => Ok(None),
-                        }
-                    }
-                    None => Ok(None),
-                }
+                let (count, oldest) = conn.query_row(
+                    "SELECT COUNT(*), MIN(run_after) FROM tasks WHERE status='pending'",
+                    [],
+                    |row| Ok((row.get::<_, i64>(0)?, row.get::<_, Option<f64>>(1)?)),
+                )?;
+                // `MIN` over zero rows is NULL, so the count is what decides.
+                Ok(match oldest {
+                    Some(oldest) if count > 0 => Some((count, oldest)),
+                    _ => None,
+                })
             })
             .await;
         match result {
@@ -461,13 +458,11 @@ impl QueueWorker {
         let result = self
             .pool
             .with_conn(|conn| {
-                let mut stmt =
-                    conn.prepare("SELECT MIN(run_after) FROM tasks WHERE status='pending'")?;
-                let mut rows = stmt.query([])?;
-                match rows.next()? {
-                    Some(row) => Ok(row.get::<_, Option<f64>>(0)?),
-                    None => Ok(None),
-                }
+                conn.query_row(
+                    "SELECT MIN(run_after) FROM tasks WHERE status='pending'",
+                    [],
+                    |row| row.get::<_, Option<f64>>(0),
+                )
             })
             .await;
         match result {

crates/xmedia-bot/src/send/upload.rs

@@ -170,7 +170,7 @@ pub(super) async fn prepare_upload_item(
     let media_url = item_url(&item);
     if !media_url.starts_with("http://") && !media_url.starts_with("https://") {
         let media = media_from_file(&item, std::path::PathBuf::from(media_url), caption)
-        .map_err(|message| FallbackError::Permanent { message })?;
+            .map_err(|message| FallbackError::Permanent { message })?;
         return Ok(PreparedItem {
             index,
             media,

crates/xmedia-bot/src/state.rs

@@ -3,6 +3,7 @@
 
 use crate::db::unix_now;
 use parking_lot::Mutex;
+use rusqlite::OptionalExtension;
 use rusqlite::params;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
@@ -64,12 +65,12 @@ impl ChatStore {
                 // Concurrent handler tasks (batch-forwards) may write chat_state
                 // while this read runs; the shared busy timeout handles the
                 // write-lock collision instead of failing the query.
-                let mut stmt = conn.prepare("SELECT payload FROM chat_state WHERE chat_id = ?1")?;
-                let mut rows = stmt.query(params![chat_key])?;
-                match rows.next()? {
-                    Some(row) => Ok(Some(row.get::<_, String>(0)?)),
-                    None => Ok(None),
-                }
+                conn.query_row(
+                    "SELECT payload FROM chat_state WHERE chat_id = ?1",
+                    params![chat_key],
+                    |row| row.get::<_, String>(0),
+                )
+                .optional()
             })
             .await
             .unwrap_or_else(|e| {