fix: defensive hardening — lock release logging, SQLite param guard, vector cast

Three defensive improvements found via peer code review:

1. lock.rs: Lock release errors were silently discarded with `let _ =`.
   If the DELETE failed (disk full, corruption), the lock stayed in the
   database with no diagnostic. Next sync would require --force with no
   clue why. Now logs with error!() including the underlying error message.

2. filters.rs: Dynamic SQL label filter construction had no upper bound
   on bind parameters. With many combined filters, param_idx + labels.len()
   could exceed SQLite's 999-parameter limit, producing an opaque error.
   Added a guard that caps labels at 900 - param_idx.

3. vector.rs: max_chunks_per_document returned i64 which was cast to
   usize. A negative value from a corrupt database would wrap to a huge
   number, causing overflow in the multiplier calculation. Now clamped
   to .max(1) and cast via unsigned_abs().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/core/lock.rs

@@ -121,12 +121,17 @@ impl AppLock {
             let _ = handle.join();
         }
 
-        let _ = self.conn.execute(
+        match self.conn.execute(
             "DELETE FROM app_locks WHERE name = ? AND owner = ?",
             (&self.name, &self.owner),
-        );
-
-        info!(owner = %self.owner, "Lock released");
+        ) {
+            Ok(_) => info!(owner = %self.owner, "Lock released"),
+            Err(e) => error!(
+                owner = %self.owner,
+                error = %e,
+                "Failed to release lock; may require --force on next sync"
+            ),
+        }
     }
 
     fn start_heartbeat(&mut self) {

src/search/filters.rs

@@ -98,15 +98,22 @@ pub fn apply_filters(
     }
 
     if !filters.labels.is_empty() {
-        let placeholders: Vec<String> = (0..filters.labels.len())
+        // SQLite has a default limit of 999 bind parameters.
+        let max_labels = 900_usize.saturating_sub(param_idx);
+        let label_slice = if filters.labels.len() > max_labels {
+            &filters.labels[..max_labels]
+        } else {
+            &filters.labels
+        };
+        let placeholders: Vec<String> = (0..label_slice.len())
             .map(|i| format!("?{}", param_idx + i))
             .collect();
         sql.push_str(&format!(
             " AND EXISTS (SELECT 1 FROM document_labels dl WHERE dl.document_id = d.id AND dl.label_name IN ({}) GROUP BY dl.document_id HAVING COUNT(DISTINCT dl.label_name) = {})",
             placeholders.join(","),
-            filters.labels.len()
+            label_slice.len()
         ));
-        for label in &filters.labels {
+        for label in label_slice {
             params.push(Box::new(label.clone()));
             param_idx += 1;
         }

src/search/vector.rs

@@ -50,8 +50,8 @@ pub fn search_vector(
         .flat_map(|f| f.to_le_bytes())
         .collect();
 
-    let max_chunks = max_chunks_per_document(conn);
-    let multiplier = ((max_chunks as usize * 3 / 2) + 1).max(8);
+    let max_chunks = max_chunks_per_document(conn).max(1);
+    let multiplier = ((max_chunks.unsigned_abs() as usize * 3 / 2) + 1).max(8);
     let k = limit * multiplier;
 
     let mut stmt = conn.prepare(