Fixes #3872. pkg/platform/yaml/testdb/util.go decoded the noise assertion sub-map by asserting:

noiseMap, ok := raw.(map[models.AssertionType]interface{})

YAML never decodes a sub-map into that custom-typed key, yaml.v3 produces map[string]interface{}, yaml.v2 produces map[interface{}]interface{}. The assertion always failed, the Debug log fired, and tc.Noise stayed empty. Users' noise configurations were silently dropped during test replay.

Change

Extracted a populateNoise(raw, noise) helper that:

• Accepts map[string]interface{} (yaml.v3), map[interface{}]interface{} (yaml.v2), and map[string][]string (programmatic round-trips).
• Iterates entries, initialising noise[field] = []string{} (preserves the existing 'empty key still present' behaviour) and accepting both []interface{} and []string for the inner values.

Both the HTTP and gRPC branches in DecodeTestcase now delegate to this helper, eliminating the duplicate buggy block.

Test plan

• go build ./pkg/platform/yaml/testdb/..., clean
• go vet ./pkg/platform/yaml/testdb/..., clean
• go test ./pkg/platform/yaml/testdb/..., all existing tests pass
• New noise_decode_test.go covers all three input shapes (yaml.v3 map, yaml.v2 map, concrete map[string][]string)
• Pre-fix the existing pattern raw.(map[models.AssertionType]interface{}) returns ok == false for every yaml-decoded shape (asserted by tracing the test inputs)

Customer-data hygiene

No real recordings or customer data introduced. Test inputs use synthetic header names (X-Request-ID, Cookie) and field paths (body.timestamp).