fix(ingestion): consistent error handling in search walk

Both walk-level errors and ReadFile failures now use best-effort
semantics (warn via slog, continue) instead of mixed abort/silent-skip.
filepath.Rel error is now propagated from the callback instead of
discarded.

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

ingestion/internal/search/search.go

@@ -3,6 +3,8 @@ package search
 
 import (
 	"bufio"
+	"fmt"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"sort"
@@ -32,13 +34,18 @@ func Query(brainDir, query string, limit int) ([]Result, error) {
 	var results []Result
 
 	err := filepath.WalkDir(filepath.Join(brainDir, "wiki"), func(path string, d os.DirEntry, err error) error {
-		if err != nil || d.IsDir() || !strings.HasSuffix(path, ".md") {
+		if err != nil {
-			return err
+			slog.Warn("search: skipping path", "path", path, "err", err)
+			return nil
+		}
+		if d.IsDir() || !strings.HasSuffix(path, ".md") {
+			return nil
 		}
 
 		content, err := os.ReadFile(path)
 		if err != nil {
-			return nil // skip unreadable files
+			slog.Warn("search: skipping unreadable file", "path", path, "err", err)
+			return nil
 		}
 
 		lower := strings.ToLower(string(content))
@@ -50,7 +57,10 @@ func Query(brainDir, query string, limit int) ([]Result, error) {
 			return nil
 		}
 
-		rel, _ := filepath.Rel(brainDir, path)
+		rel, err := filepath.Rel(brainDir, path)
+		if err != nil {
+			return fmt.Errorf("rel path: %w", err)
+		}
 		rel = filepath.ToSlash(rel)
 
 		results = append(results, Result{