Declare only the tables and columns pixa writes and reads (closes #310)

Removes output_content and request_cache, which nothing writes, and every
column that was written but never read: the host, path, query, content_type
and fetched_at of source_content, the content_type and created_at of
variant_content, and the status_code, error_message and fetched_at of
negative_cache.

StoreSource no longer takes the fetch result and LookupSource returns only
the source key. StoreVariant no longer takes a content type and
StoreNegative no longer takes a status code or message, so
extractStatusCode and the status constants, which only fed status_code,
are gone. Reconciliation adopts a variant file without opening it, as its
row no longer records a content type. Tests that set or checked a removed
column follow.

Model: opus-5-5

internal/imgcache/service.go

@@ -397,7 +397,7 @@ func (s *Service) processFromSourceOrFetch(
 	cacheKey imagerequest.VariantKey,
 ) (*processedVariant, error) {
 	// Check if we have cached source content
-	sourceKey, _, err := s.cache.LookupSource(ctx, req)
+	sourceKey, err := s.cache.LookupSource(ctx, req)
 	if err != nil {
 		s.log.Warn("source lookup failed", "error", err)
 	}
@@ -458,7 +458,7 @@ func (s *Service) fetchAndProcess(
 	if err != nil {
 		// Store negative cache for certain errors
 		if isNegativeCacheable(err) {
-			s.storeNegative(ctx, req, extractStatusCode(err), err)
+			s.storeNegative(ctx, req)
 		}
 
 		return nil, fmt.Errorf("upstream fetch failed: %w", err)
@@ -512,13 +512,13 @@ func (s *Service) fetchAndProcess(
 		s.log.Warn("source refused", "request_id", middleware.GetReqID(ctx),
 			"host", req.Source.Host, "path", req.Source.Path,
 			"content_type", fetchResult.ContentType, "error", err)
-		s.storeNegative(ctx, req, httpStatusUnsupportedMediaType, err)
+		s.storeNegative(ctx, req)
 
 		return nil, fmt.Errorf("content validation failed: %w", err)
 	}
 
 	// Store source content
-	_, err = s.cache.StoreSource(ctx, req, bytes.NewReader(sourceData), fetchResult)
+	_, err = s.cache.StoreSource(ctx, req, bytes.NewReader(sourceData))
 	if err != nil {
 		s.log.Warn("failed to store source content", "error", err)
 		// Continue even if caching fails
@@ -530,15 +530,13 @@ func (s *Service) fetchAndProcess(
 }
 
 // storeNegative stores a negative cache entry for req's source, whose fetch
-// failed with err, so the source is not fetched again until the entry
-// expires. A failure to store the entry is only logged.
-func (s *Service) storeNegative(
-	ctx context.Context, req *imagerequest.Request, statusCode int, err error,
-) {
-	storeErr := s.cache.StoreNegative(ctx, req, statusCode, err.Error())
-	if storeErr != nil {
+// failed, so the source is not fetched again until the entry expires. A
+// failure to store the entry is only logged.
+func (s *Service) storeNegative(ctx context.Context, req *imagerequest.Request) {
+	err := s.cache.StoreNegative(ctx, req)
+	if err != nil {
 		s.log.Warn("failed to store negative cache entry",
-			"host", req.Source.Host, "path", req.Source.Path, "error", storeErr)
+			"host", req.Source.Host, "path", req.Source.Path, "error", err)
 	}
 }
 
@@ -614,9 +612,7 @@ func (s *Service) processAndStore(
 	)
 
 	// Store variant to cache
-	err = s.cache.StoreVariant(
-		ctx, cacheKey, bytes.NewReader(processedData), processResult.ContentType,
-	)
+	err = s.cache.StoreVariant(ctx, cacheKey, bytes.NewReader(processedData))
 	if err != nil {
 		s.log.Warn("failed to store variant", "error", err)
 		// Continue even if caching fails
@@ -629,28 +625,11 @@ func (s *Service) processAndStore(
 	}, nil
 }
 
-// HTTP status codes for error responses.
-const (
-	httpStatusBadGateway           = 502
-	httpStatusInternalError        = 500
-	httpStatusUnsupportedMediaType = 415
-)
-
 // isNegativeCacheable returns true if the error should be cached.
 func isNegativeCacheable(err error) bool {
 	return errors.Is(err, httpfetcher.ErrUpstreamError)
 }
 
-// extractStatusCode extracts HTTP status code from error message.
-func extractStatusCode(err error) int {
-	// Default to 502 Bad Gateway for upstream errors
-	if errors.Is(err, httpfetcher.ErrUpstreamError) {
-		return httpStatusBadGateway
-	}
-
-	return httpStatusInternalError
-}
-
 // etagHashLength is the number of hash characters to use for ETags.
 const etagHashLength = 16