Problem: SigV4 chunked upload checksum trailer parsing rejected mixed-case checksum header names even though HTTP header field names are case-insensitive.
Root cause: extractChecksumAlgorithm compared the x-amz-trailer value and trailer header key against exact lowercase strings.
Fix: Trim and lowercase checksum trailer header names before matching supported checksum algorithms.
Reproduction: go test ./weed/s3api -run TestExtractChecksumAlgorithmIsCaseInsensitive -count=1 with X-Amz-Checksum-Crc32; before the fix it returned unsupported checksum algorithm.
Validation: gofmt -w weed/s3api/chunked_reader_v4.go weed/s3api/chunked_reader_v4_test.go; git diff --check; go test ./weed/s3api -run TestExtractChecksumAlgorithmIsCaseInsensitive -count=1; go test ./weed/s3api -count=1
Co-authored-by: Codex <noreply@openai.com>